Complete user groups/adata implementation

config/AcediaDB.ini

@@ -0,0 +1,5 @@
+;   Define all databases you want Acedia to use here.
+;   For simply making default Acedia configs work, set `createIfMissing` below
+; to `true`.
+[Database LocalDatabase]
+createIfMissing=false

config/AcediaUsers.ini

@@ -1,10 +1,30 @@
+;   Acedia requires adding its own `GameRules` to listen to many different
+; game events.
+
+;   In this config you can setup Acedia's user groups and persistent data
+; storage. Enabling this feature automatically enables user group support,
+; while persistent data is optional.
+;   Databases can be configured in `AcediaDB.ini`.
 [default Users]
-useDatabase=false
+;   Configures whether to use database (and which) for storing user groups.
-databaseLink="[local]database:/users"
+; Set `useDatabaseForGroupsData` to `false` if you want to define which users
-userGroup=admin
+; belong to what groups inside this config.
-userGroup=moderator
+useDatabaseForGroupsData=true
-userGroup=trusted
+groupsDatabaseLink=[local]Database:/group_data
+;   Configures whether persistent data should be additionally used.
+; It can only be stored inside a database.
+usePersistentData=true
+persistentDataDatabaseLink=[local]Database:/user_data
+; Available groups. Only used if `useDatabaseForGroupsData` is set to `false`.
+localUserGroup=admin
+localUserGroup=moderator
+localUserGroup=trusted
 
+;   These groups definitions only work in case you're using a config with
+; `useDatabaseForGroupsData` set to `false`. Simply add new `user=` record,
+; specifying SteamIDs of the players, e.g. `user=76561197960287930`.
+;   You can also optionally specify a human-readable lable for the SteamID after
+; slash "/", e.g. `user=76561197960287930/gabe`.
 [admin UserGroup]
 ;user=
 
@@ -12,6 +32,4 @@ userGroup=trusted
 ;user=
 
 [trusted UserGroup]
-;user=
+;user=
-
-; ?wanted, banned?

sources/BaseRealm/AcediaEnvironment/AcediaEnvironment.uc

@@ -414,6 +414,7 @@ public final function Feature GetEnabledFeature(class<Feature> featureClass)
 
 /**
  *  Enables given `Feature` instance `newEnabledFeature` with a given config.
+ *  Does not change a config for already enabled feature, failing instead.
  *
  *  @see `Feature::EnableMe()`.
  *

sources/Data/Collections/ArrayList.uc

@@ -5,7 +5,7 @@
  *  `AcediaObject`s.
  *      Appropriate classes and APIs for their construction are provided for
  *  main primitive types and can be extended to any custom `struct`.
- *      Copyright 2022 Anton Tarasenko
+ *      Copyright 2022-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -24,6 +24,7 @@
  */
 class ArrayList extends Collection;
 
+var bool FLAG;
 //  Actual storage of all our data.
 var private array<AcediaObject> storedObjects;
 
@@ -54,6 +55,34 @@ public final function int GetLength()
     return storedObjects.length;
 }
 
+/**
+ *  Appends objects from another `ArrayList` to the caller one.
+ *
+ *  @param  other   Array to append objects from. `none` means nothing will be
+ *      added.
+ *  @return Reference to the caller `ArrayList` to allow for method chaining.
+ */
+public final function ArrayList Append(ArrayList other)
+{
+    local int                   i, shift;
+    local array<AcediaObject>   otherObjects;
+
+    if (other == none)          return self;
+    if (other.GetLength() <= 0) return self;
+
+    shift = storedObjects.length;
+    otherObjects = other.storedObjects;
+    SetLength(storedObjects.length + otherObjects.length);
+    for (i = 0; i < otherObjects.length; i += 1)
+    {
+        if (otherObjects[i] != none) {
+            otherObjects[i].NewRef();
+        }
+        storedObjects[i + shift] = otherObjects[i];
+    }
+    return self;
+}
+
 /**
  *      Changes length of the caller `ArrayList`.
  *      If `ArrayList` size is increased as a result - added items will be
@@ -67,12 +96,15 @@ public final function ArrayList SetLength(int newLength)
 {
     local int i;
 
-    if (newLength < 0) {
+    if (newLength < 0)                      return self;
-        return self;
+    if (storedObjects.length == newLength)  return self;
-    }
+
     for (i = newLength; i < storedObjects.length; i += 1) {
         FreeItem(i);
     }
+    if (storedObjects.length <= 0) {
+        storedObjects[0] = none;
+    }
     storedObjects.length = newLength;
     return self;
 }
@@ -218,20 +250,15 @@ public final function ArrayList RemoveIndex(int index)
 }
 
 /**
- *  Validates item at `index`: in case it was erroneously deallocated while
+ *  Validates item at `index`: whether it fits in current array bounds.
- *  being stored in caller `ArrayList` - forgets stored `AcediaObject`
- *  reference.
  *
- *  @param  index   Index of an item to validate/
+ *  @param  index   Index of an item to validate.
  *  @return `true` if `index` is valid for `storedObjects` array.
  */
 private final function bool ValidateIndex(int index)
 {
-    local AcediaObject item;
-
     if (index < 0)                      return false;
     if (index >= storedObjects.length)  return false;
-    item = storedObjects[index];
 
     return true;
 }
@@ -429,7 +456,40 @@ public final function int Find(AcediaObject item)
     return -1;
 }
 
-protected function AcediaObject GetByText(BaseText key)
+/**
+ *  `ArrayList` only support `IntBox` and `IntRef` indices for this method.
+ */
+public function bool HasKey(AcediaObject key)
+{
+    if (key == none) {
+        return false;
+    }
+    else if (key.class == class'IntBox') {
+        return ValidateIndex(IntBox(key).Get());
+    }
+    else if (key.class == class'IntRef') {
+        return ValidateIndex(IntRef(key).Get());
+    }
+    return false;
+}
+
+public function bool HasKeyByText(Text key)
+{
+    local int       index, consumed;
+    local Parser    parser;
+
+    parser = _.text.Parse(key);
+    parser.MUnsignedInteger(index,,, consumed);
+    if (!parser.Ok())
+    {
+        parser.FreeSelf();
+        return false;
+    }
+    parser.FreeSelf();
+    return ValidateIndex(index);
+}
+
+public function AcediaObject GetByText(Text key)
 {
     local int       index, consumed;
     local Parser    parser;

sources/Data/Collections/Collection.uc

@@ -2,7 +2,7 @@
  *      Acedia provides a small set of collections for easier data storage.
  *      This is their base class that provides a simple interface for
  *  common methods.
- *      Copyright 2020 - 2022 Anton Tarasenko
+ *      Copyright 2020-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -25,18 +25,46 @@ class Collection extends AcediaObject
 var protected class<CollectionIterator> iteratorClass;
 
 /**
- *  Method that must be overloaded for `GetItemByPointer()` to properly work.
+ *  Checks if caller `Collection` has value recorded with a given `key`.
  *
- *      This method must return an item that `key` refers to with it's
+ *  Not all collections must support all possible types of keys.
- *  textual content (not as an object itself).
+ *  Key equality is determined by `AcediaObject::IsEqual()` method.
+ *
+ *  @return `true` if caller `Collection` has value recorded with
+ *      a given `key` and `false` otherwise.
+ */
+public function bool HasKey(AcediaObject key);
+
+/**
+ *  Checks if caller `Collection` has value that a given `key` refers to with
+ *  its textual content (not as an object itself).
  *      For example, `ArrayList` parses it into unsigned number, while
  *  `HashTable` uses it as a key directly.
+ *      There is no requirement that all stored values must be reachable by
+ *  this method (i.e. `HashTable` only lets you access values with
+ *  `Text` keys).
  *
+ *  @return `true` if caller `Collection` has value recorded with
+ *      a given `key` (understood within its textual content) and `false`
+ *      otherwise.
+ */
+public function bool HasKeyByText(Text key);
+
+/**
+ *      This method must return an item that `key` refers to with its
+ *  textual content (not as an object itself).
+ *      For example, `ArrayList` parses it into unsigned number, while
+ *  `HashTable` uses it as a key directly.
  *      There is no requirement that all stored values must be reachable by
  *  this method (i.e. `HashTable` only lets you access values with
  *  `Text` keys).
+ *
+ *  To check whether such value even exists in the collection @see HasKeyByText.
+ *
+ *  @param  key Key that refers to the value to return.
+ *  @return Value that `key` refers to with its textual content.
  */
-protected function AcediaObject GetByText(BaseText key);
+public function AcediaObject GetByText(Text key);
 
 /**
  *  Creates an `Iterator` instance to iterate over stored items.
@@ -88,7 +116,7 @@ public function Empty() {}
  *  this method (i.e. `HashTable` only lets you access values with `Text` keys).
  *
  *  @param  jsonPointer Path, given by a JSON pointer.
- *  @return An item `jsonPointerAsText` is referring to (according to the above
+ *  @return An item `jsonPointer` is referring to (according to the above
  *      stated rules). `none` if such item does not exist.
  */
 public final function AcediaObject GetItemByJSON(JSONPointer jsonPointer)
@@ -522,7 +550,35 @@ public final function Text GetTextBy(BaseText jsonPointerAsText)
 }
 
 /**
- *  Returns an `HashTable` value (stored in the caller `Collection` or
+ *  Returns a generic `Collection` value (stored in the caller `Collection` or
+ *  one of it's sub-collections) pointed by
+ *  [JSON pointer](https://tools.ietf.org/html/rfc6901).
+ *  See `GetItemBy()` for more information.
+ *
+ *  Referred value must be stored as `Collection`
+ *  (or one of it's sub-classes) for this method to work.
+ *
+ *  @param  jsonPointerAsText   Description of a path to the `Collection` value.
+ *  @return `Collection` value, stored at `jsonPointerAsText` or
+ *      `none` if it is missing or has a different type.
+ */
+public final function Collection GetCollectionBy(
+    BaseText jsonPointerAsText)
+{
+    local Collection    asCollection;
+    local AcediaObject  result;
+
+    result = GetItemBy(jsonPointerAsText);
+    asCollection = Collection(result);
+    if (asCollection != none) {
+        return asCollection;
+    }
+    _.memory.Free(result);
+    return none;
+}
+
+/**
+ *  Returns a `HashTable` value (stored in the caller `Collection` or
  *  one of it's sub-collections) pointed by
  *  [JSON pointer](https://tools.ietf.org/html/rfc6901).
  *  See `GetItemBy()` for more information.
@@ -904,7 +960,34 @@ public final function Text GetTextByJSON(JSONPointer jsonPointer)
 }
 
 /**
- *  Returns an `HashTable` value (stored in the caller `Collection` or
+ *  Returns a generic `Collection` value (stored in the caller `Collection` or
+ *  one of it's sub-collections) pointed by JSON pointer.
+ *  See `GetItemByJSON()` for more information.
+ *
+ *  Referred value must be stored as `Collection`
+ *  (or one of it's sub-classes) for this method to work.
+ *
+ *  @param  jsonPointer JSON path to the `Collection` value.
+ *  @return `Collection` value, stored at `jsonPointerAsText` or
+ *      `none` if it is missing or has a different type.
+ */
+public final function Collection GetCollectionByJSON(
+    JSONPointer jsonPointer)
+{
+    local AcediaObject  result;
+    local Collection    asCollection;
+
+    result = GetItemByJSON(jsonPointer);
+    asCollection = Collection(result);
+    if (asCollection != none) {
+        return asCollection;
+    }
+    _.memory.Free(result);
+    return none;
+}
+
+/**
+ *  Returns a `HashTable` value (stored in the caller `Collection` or
  *  one of it's sub-collections) pointed by JSON pointer.
  *  See `GetItemByJSON()` for more information.
  *

sources/Data/Collections/HashTable.uc

@@ -197,6 +197,37 @@ private final function ResizeHashTable(int newSize)
     }
 }
 
+/**
+ *  Appends objects from another `HashTable` to the caller one.
+ *
+ *  @param  other   Array to append objects from. `none` means nothing will be
+ *      added.
+ *  @return Reference to the caller `HashTable` to allow for method chaining.
+ */
+public final function HashTable Append(HashTable other)
+{
+    local AcediaObject      nextKey, nextValue;
+    local HashTableIterator iter;
+
+    if (other == none)          return self;
+    if (other.GetLength() <= 0) return self;
+
+    iter = HashTableIterator(other.Iterate());
+    while (!iter.HasFinished())
+    {
+        nextKey     = iter.GetKey();
+        nextValue   = iter.Get();
+        if (!HasKey(nextKey)) {
+            SetItem(nextKey, nextValue);
+        }
+        _.memory.Free(nextKey);
+        _.memory.Free(nextValue);
+        iter.Next();
+    }
+    _.memory.Free(iter);
+    return self;
+}
+
 /**
  *  Returns minimal capacity of the caller associative array.
  *
@@ -234,19 +265,18 @@ public final function SetMinimalCapacity(int newMinimalCapacity)
     UpdateHashTableSize();
 }
 
-/**
+public function bool HasKey(AcediaObject key)
- *  Checks if caller `HashTable` has value recorded with a given `key`.
- *
- *  @return `true` if caller `HashTable` has value recorded with
- *      a given `key` and `false` otherwise.
- */
-public final function bool HasKey(AcediaObject key)
 {
     local int bucketIndex, entryIndex;
 
     return FindEntryIndices(key, bucketIndex, entryIndex);
 }
 
+public function bool HasKeyByText(Text key)
+{
+    return HasKey(key);
+}
+
 /**
  *  Returns borrowed value recorded by a given key `key` in the caller
  *  `HashTable`.
@@ -629,7 +659,7 @@ public final function AcediaObject GetKeyByIndex(Index index)
     return key.NewRef();
 }
 
-protected function AcediaObject GetByText(BaseText key)
+public function AcediaObject GetByText(Text key)
 {
     return GetItem(key);
 }

sources/Data/Collections/Tests/TEST_ArrayList.uc

@@ -31,6 +31,7 @@ protected static function TESTS()
     Test_Find();
     Test_ReferenceManagementGet();
     Test_Take();
+    Test_Append();
 }
 
 protected static function Test_GetSet()
@@ -289,7 +290,7 @@ protected static function Test_Take()
     local array<MockItem>   allocatedItems;
 
     array = NewMockArray(20, allocatedItems);
-    Context("Testing how well `ArrayList`'s `TakeItem()` command");
+    Context("Testing how well `ArrayList`'s `TakeItem()` command.");
     Issue("`TakeItem()` return wrongs item.");
     for (i = 0; i < allocatedItems.length; i += 1)
     {
@@ -312,6 +313,55 @@ protected static function Test_Take()
     }
 }
 
+protected static function Test_Append()
+{
+    local int       i;
+    local ArrayList main, additive, empty;
+
+    main        = __().collections.EmptyArrayList();
+    additive    = __().collections.EmptyArrayList();
+    empty       = __().collections.EmptyArrayList();
+    //  Ref counter = 2, from creation and adding to collection
+    main.AddItem(__().box.int(76)).AddItem(__().text.FromString("yoyoyo"));
+    main.AddItem(none).AddItem(__().ref.float(34.3));
+    additive.AddItem(none).AddItem(__().ref.bool(true));
+
+    Context("Testing appending `ArrayList`'s.");
+    Issue("`Append(none)` changes caller `ArrayList`.");
+    main.Append(none);
+    TEST_ExpectTrue(__().json.Print(main).ToString()
+        == "[76,\"yoyoyo\",null,34.3]");
+
+    Issue("`Append()` doesn't properly work on empty `ArrayList`");
+    //  main ref = 3, +1 from copying
+    //  additive ref = 2 (still)
+    empty.Append(main);
+    TEST_ExpectTrue(__().json.Print(main).ToString()
+        == "[76,\"yoyoyo\",null,34.3]");
+
+    Issue("`Append()` doesn't properly append `ArrayList`s.");
+    //  main ref = 3
+    //  additive ref = 3, +1 from copying
+    main.Append(additive);
+    TEST_ExpectTrue(__().json.Print(main).ToString()
+        == "[76,\"yoyoyo\",null,34.3,null,true]");
+
+    Issue("`Append()` changes appended `ArrayList`");
+    TEST_ExpectTrue(__().json.Print(additive).ToString() == "[null,true]");
+
+    Issue("`Append()` incorrectly changes reference count of stored objects.");
+    //  Ref counter = 3, but will be visible as 4 from getters
+    for (i = 0; i < main.GetLength(); i += 1)
+    {
+        if (i == 2 || i == 4) {
+            TEST_ExpectNone(main.GetItem(i));
+        }
+        else {
+            TEST_ExpectTrue(main.GetItem(i)._getRefCount() == 4);
+        }
+    }
+}
+
 defaultproperties
 {
     caseGroup   = "Collections"

sources/Data/Collections/Tests/TEST_HashTable.uc

@@ -37,6 +37,7 @@ protected static function TESTS()
     Test_ReferenceManagement();
     Test_Take();
     Test_LargeArray();
+    Test_Append();
 }
 
 protected static function AcediaObject NewKey(int value)
@@ -570,6 +571,87 @@ protected static function Test_LargeArray()
     }
 }
 
+protected static function Test_Append()
+{
+    local HashTable main, additive, empty;
+
+    main        = __().collections.EmptyHashTable();
+    additive    = __().collections.EmptyHashTable();
+    empty       = __().collections.EmptyHashTable();
+    //  Ref count in main = 2, creation and copy into collection
+    main.SetItem(P("A"), __().text.FromString("value of A"));
+    main.SetItem(P("B"), __().text.FromString("value of B"));
+    main.SetItem(P("C"), __().text.FromString("value of C"));
+    main.SetItem(P("D"), none);
+    additive.SetItem(P("C"), __().text.FromString("other value of C!"));
+    additive.SetItem(P("D"), __().text.FromString("value of D"));
+    additive.SetItem(P("E"), __().text.FromString("value of E"));
+
+    Context("Testing appending `HashTable`'s.");
+    SubTest_EmptyCopies(main, additive, empty);
+    SubTest_ProperCopies(main, additive, empty);
+}
+
+protected static function SubTest_EmptyCopies(
+    HashTable main,
+    HashTable additive,
+    HashTable empty)
+{
+    Issue("`Append(none)` changes caller `HashTable`.");
+    main.Append(none);
+    TEST_ExpectTrue(main.GetLength() == 4);
+    TEST_ExpectTrue(main.GetString(P("A")) == "value of A");
+    TEST_ExpectTrue(main.GetString(P("B")) == "value of B");
+    TEST_ExpectTrue(main.GetString(P("C")) == "value of C");
+    TEST_ExpectNone(main.GetItem(P("D")));
+
+    Issue("`Append()` for empty argument changes caller `HashTable`.");
+    main.Append(empty);
+    TEST_ExpectTrue(main.GetLength() == 4);
+    TEST_ExpectTrue(main.GetString(P("A")) == "value of A");
+    TEST_ExpectTrue(main.GetString(P("B")) == "value of B");
+    TEST_ExpectTrue(main.GetString(P("C")) == "value of C");
+    TEST_ExpectNone(main.GetItem(P("D")));
+
+    Issue("`Append()` doesn't properly work on empty `HashTable`");
+    //  Ref count in main = 3,  +1 for appending
+    empty.Append(main);
+    TEST_ExpectTrue(empty.GetLength() == 4);
+    TEST_ExpectTrue(empty.GetString(P("A")) == "value of A");
+    TEST_ExpectTrue(empty.GetString(P("B")) == "value of B");
+    TEST_ExpectTrue(empty.GetString(P("C")) == "value of C");
+    TEST_ExpectNone(empty.GetItem(P("D")));
+}
+
+protected static function SubTest_ProperCopies(
+    HashTable main,
+    HashTable additive,
+    HashTable empty)
+{
+    Issue("`Append()` doesn't properly append `HashTable`s.");
+    main.Append(additive);
+    TEST_ExpectTrue(main.GetLength() == 5);
+    TEST_ExpectTrue(main.GetString(P("A")) == "value of A");
+    TEST_ExpectTrue(main.GetString(P("B")) == "value of B");
+    TEST_ExpectTrue(main.GetString(P("C")) == "value of C");
+    TEST_ExpectNone(main.GetItem(P("D")));
+    TEST_ExpectTrue(main.GetString(P("E")) == "value of E");
+
+    Issue("`Append()` changes appended `HashTable`");
+    TEST_ExpectTrue(additive.GetLength() == 3);
+    TEST_ExpectTrue(additive.GetString(P("C")) == "other value of C!");
+    TEST_ExpectTrue(additive.GetString(P("D")) == "value of D");
+    TEST_ExpectTrue(additive.GetString(P("E")) == "value of E");
+
+    Issue("`Append()` incorrectly changes reference counts of items inside"
+        @ "`HashTable`");
+    //  Ref count in main = 3, so 4 after getter
+    TEST_ExpectTrue(main.GetItem(P("A"))._getRefCount() == 4);
+    TEST_ExpectTrue(main.GetItem(P("B"))._getRefCount() == 4);
+    TEST_ExpectTrue(main.GetItem(P("C"))._getRefCount() == 4);
+    TEST_ExpectTrue(main.GetItem(P("E"))._getRefCount() == 4);
+}
+
 defaultproperties
 {
     caseGroup   = "Collections"

sources/Data/Database/Connection/DBConnection.uc

@@ -0,0 +1,791 @@
+/**
+ *  Auxiliary object for simplifying working with databases.
+ *      Copyright 2023 Anton Tarasenko
+ *------------------------------------------------------------------------------
+ * This file is part of Acedia.
+ *
+ * Acedia is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Acedia is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Acedia.  If not, see <https://www.gnu.org/licenses/>.
+ */
+class DBConnection extends AcediaObject
+    dependson(Database)
+    dependson(DBCache);
+
+/**
+ *  # `DBConnection`
+ *
+ *      Auxiliary object for simplifying working with databases.
+ *  `Database` class has a rather simple interface and there are several issues
+ *  that constantly arise when trying to use it:
+ *
+ *      1.  If one tries to read/write data from/to specific location in
+ *          the database, then `JSONPointer` has to be kept in addition to
+ *          the `Database` reference at all times;
+ *      2.  One has to perform initial checks about whether database can even be
+ *          connected to, if at desired location there is a proper data
+ *          structure, etc.. If one also wants to start using data before
+ *          database's response or after its failure, then the same work of
+ *          duplication that data locally must be performed.
+ *      3.  Instead of immediate operations, database operations are delayed and
+ *          user has to handle their results asynchronously in separate methods.
+ *
+ *      `DBConnection` takes care of these issues by providing you synchronous
+ *  methods for accessing cached version of the data at the given location that
+ *  is duplicated to the database as soon as possible (and even if its no longer
+ *  possible in the case of a failure).
+ *      `DBConnection` makes immediate changes on the local cache and reports
+ *  about possible failures with database later through signals `OnEditResult()`
+ *  (reports about success of writing operations) and `OnStateChanged()`
+ *  (reports about state changes of connected database, including complete
+ *  failures).
+ *      The only reading of database's values occurs at the moment of connecting
+ *  to it, after that all the data is read from the local cache.
+ *      Possible `DBConnection` states include:
+ *
+ *      *   `DBCS_Idle` - database was created, but not yet connected;
+ *      *   `DBCS_Connecting` - `Connect()` method was successfully called, but
+ *          its result is still unknown;
+ *      *   `DBCS_Connected` - database is connected and properly working;
+ *      *   `DBCS_Disconnected` - database was manually disconnected and now
+ *          operates solely on the local cache. Once disconnected `DBConnection`
+ *          cannot be reconnected - create a new one instead.
+ *      *   `DBCS_FaultyDatabase` - database is somehow faulty. Precise reason
+ *          can be found out with `GetError()` method:
+ *
+ *          *   `FDE_None` - no error has yet occurred;
+ *          *   `FDE_CannotReadRootData` - root data couldn't be read from
+ *              the database, most likely because of the invalid `JSONPointer`
+ *              for the root value;
+ *          *   `FDE_UnexpectedRootData` - root data was read from the database,
+ *              but has an unexpected format. `DBConnection` expects either
+ *              JSON object or array (can be specified which one) and this error
+ *              occurs if its not found at specified database's location;
+ *          *   `FDE_Unknown` - database returned `DBR_InvalidDatabase` result
+ *              for one of the queries. This is likely to happen when database
+ *              is damaged. More precise details depend on the implementation,
+ *              but result boils down to database being unusable.
+ *
+ *  ## Usage
+ *
+ *  Usage is straightforward:
+ *
+ *      1.  Initialize with appropriate database by calling `Initialize()`;
+ *      2.  Start connecting to it by calling `Connect()`;
+ *      3.  Use `ReadDataByJSON()`/`WriteDataByJSON()` to read/write into
+ *          the connected database;
+ *
+ *  You can use it transparently even if database connection fails, but if you
+ *  need to handle such failure - connect to the `OnStateChanged()` signal for
+ *  tracking `DBCS_FaultyDatabase` state and to `OnEditResult()` for tracking
+ *  success of writing operations.
+ *
+ *  ## Implementation
+ *
+ *      The brunt of work is done by `DBCache` and most of the logic in this
+ *  class is for tracking state of the connection to the database and then
+ *  reporting these changes through its own signals.
+ *      The most notable hidden functionality is tracking requests by ID -
+ *  `DBConnection` makes each request with unique ID and then stores them inside
+ *  `requestIDs` (and in case of write requests - along with corresponding
+ *  `JSONPointer` inside `queuedPointers`). This is necessary because:
+ *
+ *      1.  Even if `DBConnection` gets reallocated - as far as UnrealScript is
+ *          concerned it is still the same object, so the responses we no longer
+ *          care about will still arrive. Keeping track of the IDs that interest
+ *          us inside `requestIDs` allows us to filter out responses we no
+ *          longer care about;
+ *      2.  Tracking corresponding (to the IDs) `queuedPointers` also allow us
+ *          to know responses to which writing requests we've received.
+ *
+ *  ## Remarks
+ *
+ *  Currently `DBConnection` doesn't support important feature of *incrementing*
+ *  data that allows several sources to safely change the same value
+ *  asynchronously. We're skipping on it right now to save time as its not
+ *  really currently needed, however it will be added in the future.
+ */
+
+enum DBConnectionState
+{
+    //  `DBConnection` was created, but didn't yet attempt to connect
+    //  to database
+    DBCS_Idle,
+    //  `DBConnection` is currently connecting
+    DBCS_Connecting,
+    //  `DBConnection` has already connected without errors
+    DBCS_Connected,
+    //  `DBConnection` was manually disconnected
+    DBCS_Disconnected,
+    //  `DBConnection` was disconnected because of the database error,
+    //  @see `FaultyDatabaseError` for more.
+    DBCS_FaultyDatabase
+};
+//  Current connection state
+var private DBConnectionState currentState;
+
+enum FaultyDatabaseError
+{
+    //  No error has occurred yet
+    FDE_None,
+    //  Root data isn't available
+    FDE_CannotReadRootData,
+    //  Root data has incorrect format
+    FDE_UnexpectedRootData,
+    //  Some internal error in database has occurred
+    FDE_Unknown
+};
+//  Reason for why current state is in `DBCS_FaultyDatabase` state;
+//  `FDE_None` if `DBConnection` is in any other state.
+var private FaultyDatabaseError dbFailureReason;
+//      Keeps track whether root value read from the database was of the correct
+//  type. Only relevant after database tried connecting (i.e. it is in states
+//  `DBCS_Connected`, `DBCS_Disconnected` or `DBCS_FaultyDatabase`).
+//      This variable helps us determine whether error should be
+//  `FDE_CannotReadRootData` or `FDE_UnexpectedRootData`.
+var private bool                rootIsOfExpectedType;
+
+//  `Database` + `JSONPointer` combo that point at the data we want to
+//  connect to
+var private Database    dbInstance;
+var private JSONPointer rootPointer;
+//  Local, cached version of that data
+var private DBCache     localCache;
+
+//  This is basically an array of (`int`, `JSONPointer`) pairs for tracking
+//  database requests of interest
+var private array<int>          requestIDs;
+var private array<JSONPointer>  queuedPointers;
+//  Next usable ID. `DBConnection` is expected to always use unique IDs.
+var private int                 nextRequestID;
+
+
+var private DBConnection_StateChanged_Signal    onStateChangedSignal;
+var private DBConnection_EditResult_Signal      onEditResultSignal;
+
+var private LoggerAPI.Definition errDoubleInitialization;
+
+/**
+ *  Signal that will be emitted whenever `DBConnection` changes state.
+ *  List of the available states:
+ *
+ *      *   `DBCS_Idle` - database was created, but not yet connected;
+ *      *   `DBCS_Connecting` - `Connect()` method was successfully called, but
+ *          its result is still unknown;
+ *      *   `DBCS_Connected` - database is connected and properly working;
+ *      *   `DBCS_Disconnected` - database was manually disconnected and now
+ *          operates solely on the local cache. Once disconnected `DBConnection`
+ *          cannot be reconnected - create a new one instead.
+ *      *   `DBCS_FaultyDatabase` - database is somehow faulty. Precise reason
+ *          can be found out with `GetError()` method.
+ *
+ *  This method *is not* called when `DBConnection` is deallocated.
+ *
+ *  [Signature]
+ *  void <slot>(
+ *      DBConnection        instance,
+ *      DBConnectionState   oldState,
+ *      DBConnectionState   newState)
+ *
+ *  @param  instance    Instance of the `DBConnection` that has changed state.
+ *  @param  oldState    State it was previously in.
+ *  @param  oldState    New state.
+ */
+/* SIGNAL */
+public final function DBConnection_StateChanged_Slot OnStateChanged(
+    AcediaObject receiver)
+{
+    return DBConnection_StateChanged_Slot(onStateChangedSignal
+        .NewSlot(receiver));
+}
+
+/**
+ *  Signal that will be emitted whenever `DBConnection` receives response from
+ *  connected database about success of writing operation.
+ *
+ *  Responses to old requests can still be received even if database got
+ *  disconnected.
+ *
+ *  Any emissions of this signal when the database's state is `DBCS_Connecting`
+ *  correspond to reapplying edits made prior connection was established.
+ *
+ *  [Signature]
+ *  void <slot>(JSONPointer editLocation, bool isSuccessful)
+ *
+ *  @param  editLocation    Location of the writing operation this is
+ *      a response to.
+ *  @param  isSuccessful    Whether writing operation ended in the success.
+ */
+/* SIGNAL */
+public final function DBConnection_EditResult_Slot OnEditResult(
+    AcediaObject receiver)
+{
+    return DBConnection_EditResult_Slot(onEditResultSignal.NewSlot(receiver));
+}
+
+protected function Constructor()
+{
+    localCache = DBCache(_.memory.Allocate(class'DBCache'));
+    onStateChangedSignal = DBConnection_StateChanged_Signal(
+        _.memory.Allocate(class'DBConnection_StateChanged_Signal'));
+    onEditResultSignal = DBConnection_EditResult_Signal(
+        _.memory.Allocate(class'DBConnection_EditResult_Signal'));
+}
+
+protected function Finalizer()
+{
+    rootIsOfExpectedType = false;
+    currentState = DBCS_Idle;
+    _.memory.Free(dbInstance);
+    _.memory.Free(rootPointer);
+    _.memory.Free(localCache);
+    dbInstance  = none;
+    rootPointer = none;
+    localCache  = none;
+    _.memory.FreeMany(queuedPointers);
+    queuedPointers.length = 0;
+    requestIDs.length = 0;
+    //  Free signals
+    _.memory.Free(onStateChangedSignal);
+    _.memory.Free(onEditResultSignal);
+    onStateChangedSignal    = none;
+    onEditResultSignal      = none;
+}
+
+/**
+ *  Initializes `DBConnection` with database and location to which it must be
+ *  connected.
+ *
+ *  For the initialization to be successful `DBConnection` must not yet be
+ *  initialized and `initDatabase` be not `none`.
+ *
+ *  To check whether caller `DBConnection` is initialized
+ *  @see `IsInitialized()`.
+ *
+ *  @param  initDatabase    Database with data we want to connect to.
+ *  @param  initRootPointer Location of said data in the given database.
+ *      If `none` is specified, uses root object of the database.
+ *  @return `true` if initialization was successful and `false` otherwise.
+ */
+public final function bool Initialize(
+    Database                initDatabase,
+    optional JSONPointer    initRootPointer)
+{
+    if (IsInitialized())                return false;
+    if (initDatabase == none)           return false;
+    if (!initDatabase.IsAllocated())    return false;
+
+    dbInstance = initDatabase;
+    dbInstance.NewRef();
+    if (initRootPointer != none) {
+        rootPointer = initRootPointer.Copy();
+    }
+    else {
+        rootPointer = _.json.Pointer();
+    }
+    return true;
+}
+
+/**
+ *  Reads data from the `DBConnection` at the location defined by the given
+ *  `JSONPointer`.
+ *
+ *  If data was initialized with non-empty location for the root data, then
+ *  actual returned data's location in the database is defined by appending
+ *  given `pointer` to that root pointer.
+ *
+ *  Data is actually always read from the local cache and, therefore, we can
+ *  read data we've written via `DBConnection` even without actually connecting
+ *  to the database.
+ *
+ *  @param  pointer Location from which to read the data.
+ *  @return Data recorded for the given `JSONPointer`. `none` if it is missing.
+ */
+public final function AcediaObject ReadDataByJSON(JSONPointer pointer)
+{
+    return localCache.Read(pointer);
+}
+
+/**
+ *  Writes given data into the `DBConnection` at the location defined by
+ *  the given `JSONPointer`.
+ *
+ *  If data was initialized with non-empty location for the root data, then
+ *  actual location for writing data in the database is defined by appending
+ *  given `pointer` to that root pointer.
+ *
+ *      Data is actually always also written into the local cache, even when
+ *  there is no connection to the database. Once connection is made - all valid
+ *  changes will be duplicated into it.
+ *      Success of failure of actually making changes into the database can be
+ *  tracked with `OnEditResult()` signal.
+ *
+ *      This operation also returns immediate indication of whether it has
+ *  failed *locally*. This can happen when trying to perform operation
+ *  impossible for the local cache. For example, we cannot write any data at
+ *  location "/a/b/c" for the JSON object "{"a":45.6}".
+ *      If operation ended in failure locally, then change to database won't
+ *  even be attempted.
+ *
+ *  @param  pointer Location into which to write the data.
+ *  @param  data    Data to write into the connection.
+ *  @return `true` on success and `false` on failure. `true` is required for
+ *      the writing database request to be made.
+ */
+public final function bool WriteDataByJSON(
+    JSONPointer     pointer,
+    AcediaObject    data)
+{
+    if (pointer == none) {
+        return false;
+    }
+    if (localCache.Write(pointer, data))
+    {
+        ModifyDataInDatabase(pointer, data, false);
+        return true;
+    }
+    return false;
+}
+
+/**
+ *  Increments given data into the `DBConnection` at the location defined by
+ *  the given `JSONPointer`.
+ *
+ *  If data was initialized with non-empty location for the root data, then
+ *  actual location for incrementing data in the database is defined by
+ *  appending given `pointer` to that root pointer.
+ *
+ *      Data is actually always also incremented into the local cache, even when
+ *  there is no connection to the database. Once connection is made - all valid
+ *  changes will be duplicated into it.
+ *      Success of failure of actually making changes into the database can be
+ *  tracked with `OnEditResult()` signal.
+ *
+ *      This operation also returns immediate indication of whether it has
+ *  failed *locally*. This can happen when trying to perform operation
+ *  impossible for the local cache. For example, we cannot increment any data at
+ *  location "/a/b/c" for the JSON object "{"a":45.6}".
+ *      If operation ended in failure locally, then change to database won't
+ *  even be attempted.
+ *
+ *  @param  pointer Location at which to increment the data.
+ *  @param  data    Data with which to increment value inside the connection.
+ *  @return `true` on success and `false` on failure. `true` is required for
+ *      the incrementing database request to be made.
+ */
+public final function bool IncrementDataByJSON(
+    JSONPointer     pointer,
+    AcediaObject    data)
+{
+    if (pointer == none) {
+        return false;
+    }
+    if (localCache.Increment(pointer, data))
+    {
+        ModifyDataInDatabase(pointer, data, true);
+        return true;
+    }
+    return false;
+}
+
+/**
+ *  Removes data from the `DBConnection` at the location defined by the given
+ *  `JSONPointer`.
+ *
+ *  If data was initialized with non-empty location for the root data, then
+ *  actual location at which to remove data in the database is defined by
+ *  appending given `pointer` to that root pointer.
+ *
+ *      Data is actually always also removed from the local cache, even when
+ *  there is no connection to the database. Once connection is made - all valid
+ *  changes will be duplicated into it.
+ *      Success of failure of actually making changes into the database can be
+ *  tracked with `OnEditResult()` signal.
+ *
+ *      This operation also returns immediate indication of whether it has
+ *  failed *locally*.
+ *      If operation ended in failure locally, then change to database won't
+ *  even be attempted.
+ *
+ *  @param  pointer Location at which to remove data.
+ *  @return `true` on success and `false` on failure. `true` is required for
+ *      the removal database request to be made.
+ */
+public final function bool RemoveDataByJSON(JSONPointer pointer)
+{
+    if (pointer == none) {
+        return false;
+    }
+    if (localCache.Remove(pointer))
+    {
+        RemoveDataInDatabase(pointer);
+        return true;
+    }
+    return false;
+}
+
+private final function ModifyDataInDatabase(
+    JSONPointer     pointer,
+    AcediaObject    data,
+    bool            increment)
+{
+    local JSONPointer dataPointer;
+
+    if (currentState != DBCS_Connected) {
+        return;
+    }
+    dataPointer = rootPointer.Copy();
+    dataPointer.Append(pointer);
+    //  `dataPointer` is consumed by `RegisterNextRequestID()` method
+    if (increment)
+    {
+        dbInstance
+            .IncrementData(
+                dataPointer,
+                data,
+                RegisterNextRequestID(dataPointer))
+            .connect = EditDataHandler;
+    }
+    else
+    {
+        dbInstance
+            .WriteData(dataPointer, data, RegisterNextRequestID(dataPointer))
+            .connect = EditDataHandler;
+    }
+}
+
+private final function RemoveDataInDatabase(JSONPointer pointer)
+{
+    local JSONPointer dataPointer;
+
+    if (currentState != DBCS_Connected) {
+        return;
+    }
+    dataPointer = rootPointer.Copy();
+    dataPointer.Append(pointer);
+    //  `dataPointer` is consumed by `RegisterNextRequestID()` method
+    dbInstance
+        .RemoveData(dataPointer, RegisterNextRequestID(dataPointer))
+        .connect = EditDataHandler;
+}
+
+/**
+ *  Checks caller `DBConnection` was successfully initialized.
+ *
+ *  @return `true` if caller `DBConnection` was initialized and `false`
+ *      otherwise.
+ */
+public final function bool IsInitialized()
+{
+    return (dbInstance != none);
+}
+
+/**
+ *  Returns current state of the connection of `DBConnection` to the database
+ *  it was initialized with.
+ *
+ *  @see `OnStateChanged()` for more information about connection states.
+ *  @return Current connection state.
+ */
+public final function DBConnectionState GetConnectionState()
+{
+    return currentState;
+}
+
+/**
+ *  Checks whether caller `DBConnection` is currently connected without errors
+ *  to the database it was initialized with.
+ *
+ *  @return `true` if caller `DBConnection` is connected to the database and
+ *      `false` otherwise.
+ */
+public final function bool IsConnected()
+{
+    return (currentState == DBCS_Connected);
+}
+
+/**
+ *  Checks whether an error has occurred with connection to the database.
+ *
+ *      `DBConnection` can get disconnected from database manually and without
+ *  any errors, so, if you simply want to check whether connection exists,
+ *  @see `IsConnected()` or @see `GetConnectionState()`.
+ *      To obtain more detailed information @see `GetError()`.
+ *
+ *  @return `true` if there were no error thus far and `false` otherwise.
+ */
+public final function bool IsOk()
+{
+    return (dbFailureReason == FDE_None);
+}
+
+/**
+ *  Returns error that has occurred during connection.
+ *
+ *  @return Error that has occurred during connection to the database,
+ *      `FDE_None` if there was no errors.
+ */
+public final function FaultyDatabaseError GetError()
+{
+    return dbFailureReason;
+}
+
+private final function ChangeState(DBConnectionState newState)
+{
+    local DBConnectionState oldState;
+
+    oldState = currentState;
+    currentState = newState;
+    onStateChangedSignal.Emit(self, oldState, newState);
+}
+
+/**
+ *  Attempts connection to the database caller `DBConnection` was initialized
+ *  with. Result isn't immediate and can be tracked with `OnStateChanged()`
+ *  signal.
+ *
+ *  Connection checks whether data by the initialization address can be read and
+ *  has proper type (by default JSON object, but JSON array can be used
+ *  instead).
+ *
+ *  Whether connection is successfully established isn't known at the moment
+ *  this function returns. User `OnStateChanged()` to track that.
+ *
+ *  @param  expectArray Set this to `true` if the expected root value is
+ *      JSON array.
+ */
+public final function Connect(optional bool expectArray)
+{
+    local Collection incrementObject;
+
+    if (!IsInitialized())           return;
+    if (currentState != DBCS_Idle)  return;
+
+    if (expectArray) {
+        incrementObject = _.collections.EmptyArrayList();
+    }
+    else {
+        incrementObject = _.collections.EmptyHashTable();
+    }
+    dbInstance.IncrementData(
+        rootPointer,
+        incrementObject,
+        RegisterNextRequestID()).connect = IncrementCheckHandler;
+    incrementObject.FreeSelf();
+    //  Copy of the `rootPointer` is consumed by `RegisterNextRequestID()`
+    //  method
+    dbInstance.ReadData(rootPointer,, RegisterNextRequestID(rootPointer.Copy()))
+        .connect = InitialLoadingHandler;
+    ChangeState(DBCS_Connecting);
+}
+
+/**
+ *  Disconnects `DBConnection` from its database, preventing its further
+ *  updates.
+ *
+ *  Database can only be disconnected if connection was at least initialized
+ *  (state isn't `DBCS_Idle`) and no error has yet occurred (state isn't
+ *  `DBCS_FaultyDatabase`).
+ *
+ *  @return `true` if `DBConnection` was disconnected from the database and
+ *      `false` otherwise (including if it already was disconnected).
+ */
+public final function bool Disconnect()
+{
+    if (    currentState != DBCS_FaultyDatabase
+        &&  currentState != DBCS_Idle
+        &&  currentState != DBCS_Disconnected)
+    {
+        ChangeState(DBCS_Disconnected);
+        return true;
+    }
+    return false;
+}
+
+private final function int RegisterNextRequestID(
+    optional /*take*/ JSONPointer relativePointer)
+{
+    if (relativePointer != none) {
+        queuedPointers[queuedPointers.length] = relativePointer;
+    }
+    else {
+        queuedPointers[queuedPointers.length] = _.json.Pointer();
+    }
+    requestIDs[requestIDs.length] = nextRequestID;
+    nextRequestID += 1;
+    return (nextRequestID - 1);
+}
+
+private final function JSONPointer FetchRequestPointer(int requestID)
+{
+    local int           i;
+    local JSONPointer   result;
+
+    while (i < requestIDs.length)
+    {
+        if (requestIDs[i] < requestID)
+        {
+            //  We receive all requests in order, so if `requestID` is higher
+            //  than IDs of some other requests - it means that they are older,
+            //  lost requests
+            _.memory.Free(queuedPointers[i]);
+            queuedPointers.Remove(i, 1);
+            requestIDs.Remove(i, 1);
+        }
+        if (requestIDs[i] == requestID)
+        {
+            result = queuedPointers[i];
+            queuedPointers.Remove(i, 1);
+            requestIDs.Remove(i, 1);
+            return result;
+        }
+        i += 1;
+    }
+    return none;
+}
+
+private final function bool FetchIfRequestStillValid(int requestID)
+{
+    local JSONPointer result;
+
+    result = FetchRequestPointer(requestID);
+    if (result != none)
+    {
+        _.memory.Free(result);
+        return true;
+    }
+    return false;
+}
+
+private final function IncrementCheckHandler(
+    Database.DBQueryResult  result,
+    Database                source,
+    int                     requestID)
+{
+    if (!FetchIfRequestStillValid(requestID)) {
+        return;
+    }
+    //  If we could successfully increment value with appropriate JSON value,
+    //  then its type is correct
+    rootIsOfExpectedType = (result == DBR_Success);
+}
+
+private final function InitialLoadingHandler(
+    Database.DBQueryResult  result,
+    /*take*/ AcediaObject   data,
+    Database                source,
+    int                     requestID)
+{
+    local int                           i;
+    local array<DBCache.PendingEdit>    completedEdits;
+
+    if (!FetchIfRequestStillValid(requestID))
+    {
+        _.memory.Free(data);
+        return;
+    }
+    if (HandleInitializationError(result))
+    {
+        _.memory.Free(data);
+        return;
+    }
+    completedEdits = localCache.SetRealData(data);
+    for (i = 0; i < completedEdits.length; i += 1)
+    {
+        if (completedEdits[i].successful)
+        {
+            if (completedEdits[i].type == DBCET_Remove) {
+                RemoveDataInDatabase(completedEdits[i].location);
+            }
+            else
+            {
+                ModifyDataInDatabase(
+                    completedEdits[i].location,
+                    completedEdits[i].data,
+                    completedEdits[i].type == DBCET_Increment);
+            }
+        }
+        else {
+            onEditResultSignal.Emit(completedEdits[i].location, false);
+        }
+        _.memory.Free(completedEdits[i].location);
+        _.memory.Free(completedEdits[i].data);
+    }
+    _.memory.Free(data);
+    ChangeState(DBCS_Connected);
+}
+
+//  Return `true` if further initialization must be stopped.
+private final function bool HandleInitializationError(
+    Database.DBQueryResult result)
+{
+    //  Get disconnected before even response has even arrived
+    if (currentState == DBCS_Disconnected) {
+        return true;
+    }
+    if (currentState == DBCS_Connected)
+    {
+        _.logger.Auto(errDoubleInitialization).Arg(rootPointer.ToText());
+        return true;
+    }
+    if (result == DBR_InvalidDatabase)
+    {
+        dbFailureReason = FDE_Unknown;
+        ChangeState(DBCS_FaultyDatabase);
+        return true;
+    }
+    if (result != DBR_Success)
+    {
+        dbFailureReason = FDE_CannotReadRootData;
+        ChangeState(DBCS_FaultyDatabase);
+        return true;
+    }
+    if (!rootIsOfExpectedType)
+    {
+        dbFailureReason = FDE_UnexpectedRootData;
+        ChangeState(DBCS_FaultyDatabase);
+        return true;
+    }
+    return false;
+}
+
+private final function EditDataHandler(
+    Database.DBQueryResult  result,
+    Database                source,
+    int                     requestID)
+{
+    local JSONPointer relatedPointer;
+
+    relatedPointer = FetchRequestPointer(requestID);
+    if (relatedPointer == none) {
+        return;
+    }
+    if (result == DBR_InvalidDatabase)
+    {
+        dbFailureReason = FDE_Unknown;
+        ChangeState(DBCS_FaultyDatabase);
+        relatedPointer.FreeSelf();
+        return;
+    }
+    if (result == DBR_Success) {
+        onEditResultSignal.Emit(relatedPointer, true);
+    }
+    else {
+        onEditResultSignal.Emit(relatedPointer, false);
+    }
+    relatedPointer.FreeSelf();
+}
+
+defaultproperties
+{
+    errDoubleInitialization = (l=LOG_Error,m="`DBConnection` connected to \"%1\" was double-initialized. This SHOULD NOT happen. Please report this bug.")
+}

sources/Data/Database/Connection/Events/DBConnection_EditResult_Signal.uc

@@ -0,0 +1,40 @@
+/**
+ *  Signal class for `DBConnections`'s `OnEditResult()` signal.
+ *      Copyright 2023 Anton Tarasenko
+ *------------------------------------------------------------------------------
+ * This file is part of Acedia.
+ *
+ * Acedia is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Acedia is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Acedia.  If not, see <https://www.gnu.org/licenses/>.
+ */
+class DBConnection_EditResult_Signal extends Signal
+    dependson(DBConnection);
+
+public final function Emit(JSONPointer editLocation, bool isSuccessful)
+{
+    local Slot nextSlot;
+    StartIterating();
+    nextSlot = GetNextSlot();
+    while (nextSlot != none)
+    {
+        DBConnection_EditResult_Slot(nextSlot)
+            .connect(editLocation, isSuccessful);
+        nextSlot = GetNextSlot();
+    }
+    CleanEmptySlots();
+}
+
+defaultproperties
+{
+    relatedSlotClass = class'DBConnection_EditResult_Slot'
+}

sources/Data/Database/Connection/Events/DBConnection_EditResult_Slot.uc

@@ -0,0 +1,41 @@
+/**
+ *  Slot class for `DBConnections`'s `OnEditResult()` signal.
+ *      Copyright 2023 Anton Tarasenko
+ *------------------------------------------------------------------------------
+ * This file is part of Acedia.
+ *
+ * Acedia is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Acedia is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Acedia.  If not, see <https://www.gnu.org/licenses/>.
+ */
+class DBConnection_EditResult_Slot extends Slot
+    dependson(DBConnection);
+
+delegate connect(JSONPointer editLocation, bool isSuccessful)
+{
+    DummyCall();
+}
+
+protected function Constructor()
+{
+    connect = none;
+}
+
+protected function Finalizer()
+{
+    super.Finalizer();
+    connect = none;
+}
+
+defaultproperties
+{
+}

sources/Data/Database/Connection/Events/DBConnection_StateChanged_Signal.uc

@@ -0,0 +1,43 @@
+/**
+ *  Signal class for `DBConnections`'s `OnStatusChanged()` signal.
+ *      Copyright 2023 Anton Tarasenko
+ *------------------------------------------------------------------------------
+ * This file is part of Acedia.
+ *
+ * Acedia is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Acedia is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Acedia.  If not, see <https://www.gnu.org/licenses/>.
+ */
+class DBConnection_StateChanged_Signal extends Signal
+    dependson(DBConnection);
+
+public final function Emit(
+    DBConnection                    instance,
+    DBConnection.DBConnectionState  oldState,
+    DBConnection.DBConnectionState  newState)
+{
+    local Slot nextSlot;
+    StartIterating();
+    nextSlot = GetNextSlot();
+    while (nextSlot != none)
+    {
+        DBConnection_StateChanged_Slot(nextSlot)
+            .connect(instance, oldState, newState);
+        nextSlot = GetNextSlot();
+    }
+    CleanEmptySlots();
+}
+
+defaultproperties
+{
+    relatedSlotClass = class'DBConnection_StateChanged_Slot'
+}

sources/Data/Database/Connection/Events/DBConnection_StateChanged_Slot.uc

@@ -0,0 +1,44 @@
+/**
+ *  Slot class for `DBConnections`'s `OnStatusChanged()` signal.
+ *      Copyright 2023 Anton Tarasenko
+ *------------------------------------------------------------------------------
+ * This file is part of Acedia.
+ *
+ * Acedia is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Acedia is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Acedia.  If not, see <https://www.gnu.org/licenses/>.
+ */
+class DBConnection_StateChanged_Slot extends Slot
+    dependson(DBConnection);
+
+delegate connect(
+    DBConnection                    instance,
+    DBConnection.DBConnectionState  oldState,
+    DBConnection.DBConnectionState  newState)
+{
+    DummyCall();
+}
+
+protected function Constructor()
+{
+    connect = none;
+}
+
+protected function Finalizer()
+{
+    super.Finalizer();
+    connect = none;
+}
+
+defaultproperties
+{
+}

sources/Data/Database/Connection/Tests/TEST_DBConnection.uc

@@ -0,0 +1,389 @@
+/**
+ *  Set of tests for `DBConnection` and `DBCache` classes.
+ *      Copyright 2023 Anton Tarasenko
+ *------------------------------------------------------------------------------
+ * This file is part of Acedia.
+ *
+ * Acedia is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Acedia is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Acedia.  If not, see <https://www.gnu.org/licenses/>.
+ */
+class TEST_DBConnection extends TestCase
+    abstract;
+
+var DBCache cache;
+
+protected static function TESTS()
+{
+    Context("Testing how `DBCache` handles data writes and reads when"
+        @ "the actual database's data is yet to be downloaded.");
+    Test_DBCache_BasicWriteRead_DuringLoading();
+    Test_DBCache_AllOperations_DuringLoading();
+    Context("Testing how `DBCache` handles applying pending writes after real"
+        @ "data was set.");
+    Test_DBCache_ApplyingPendingEdits();
+    Test_DBCache_ApplyingPendingEdit_AllOperations();
+    Context("Testing how `DBCache` handles data writes and reads when"
+        @ "the actual database's data is already setup.");
+    Test_DBCache_BasicWriteRead_AfterLoading();
+    Test_DBCache_AllOperations_AfterLoading();
+}
+
+/*  Creates following object:
+{
+    "A": "simpleValue",
+    "B": {
+        "A": [true, {
+            "A": "simpleValue",
+            "B": 11.12,
+            "": [true, null, "huh"]
+        }, "huh"],
+        "B": -13.95
+    },
+    "C": -5,
+    "D": []
+}   */
+protected static function HashTable MakeTestJSONObject()
+{
+    local ArrayList outerArray, innerArray;
+    local HashTable result, outerObject, innerObject;
+
+    innerArray = __().collections.EmptyArrayList();
+    innerArray.AddBool(true).AddItem(none).AddString("huh");
+    innerObject = __().collections.EmptyHashTable();
+    innerObject.SetString(P("A"), "simpleValue");
+    innerObject.SetFloat(P("B"), 11.12).SetItem(P(""), innerArray);
+    outerArray = __().collections.EmptyArrayList();
+    outerArray.AddBool(true).AddItem(innerObject).AddString("huh");
+    outerObject = __().collections.EmptyHashTable();
+    outerObject.SetItem(P("A"), outerArray).SetFloat(P("B"), -13.95);
+    result = __().collections.EmptyHashTable();
+    result.SetString(P("A"), "simpleValue");
+    result.SetItem(P("B"), outerObject);
+    result.SetInt(P("C"), -5);
+    result.SetItem(P("D"), __().collections.EmptyArrayList());
+    return result;
+}
+
+protected static function CheckLocation(string pointer, string expectedResult)
+{
+    local AcediaObject value;
+
+    value = default.cache
+        .Read(__().json.Pointer(__().text.FromString(pointer)));
+    if (BaseText(value) != none)
+    {
+        TEST_ExpectTrue(
+                __().json.Print(value).ToString()
+            ==  ("\"" $ expectedResult $ "\""));
+    }
+    else {
+        TEST_ExpectTrue(__().json.Print(value).ToString() == expectedResult);
+    }
+}
+
+//      This is a rather extensive and long test.
+//  Despite its length, I've chosen to not break it up into smaller parts,
+//  since the same value `default.cache` is changed and built up all the way
+//  through this method.
+//      Trying to break it up into smaller and simpler tests would only mean
+//  putting less stress of `DBCache` than we currently do.
+protected static function Test_DBCache_BasicWriteRead_DuringLoading()
+{
+    local AcediaObject complexData;
+
+    Issue("Simple write/read sequence not working correctly.");
+    default.cache = DBCache(__().memory.Allocate(class'DBCache'));
+    complexData = MakeTestJSONObject();
+    default.cache.Write(
+        __().json.Pointer(P("/just/some/place/far/away")),
+        complexData);
+    default.cache.Write(
+        __().json.Pointer(P("/just/another/place/not/near")),
+        complexData);
+    CheckLocation("/just/another/place/not/near/A", "simpleValue");
+    CheckLocation("/just/some/place/far/away/B/A/2", "huh");
+    CheckLocation("/just/another/place/not/near/B/A/1//2", "huh");
+    CheckLocation("/just/some/place/far/away/B/A/1/", "[true,null,\"huh\"]");
+
+    Issue("Data is read incorrectly after being overridden.");
+    default.cache.Write(
+        __().json.Pointer(P("/just/another/place/not/near/B/A/1//1")),
+        __().box.bool(false));
+    CheckLocation(
+        "/just/another/place/not/near/B/A/1/",
+        "[true,false,\"huh\"]");
+    default.cache.Write(
+        __().json.Pointer(P("/just/another/place/not/near/B/A")),
+        __().box.int(121));
+    CheckLocation("/just/another/place/not/near/B/A", "121");
+    default.cache.Write(
+        __().json.Pointer(P("/just/some/place/far/away/B/A/1/B")),
+        complexData);
+    CheckLocation("/just/some/place/far/away/B/A/1/B/B/A/0", "true");
+    default.cache.Write(
+        __().json.Pointer(
+            P("/just/some/place/far/away/C/inside_the_number!/hey")),
+         __().box.float(1.1));
+    CheckLocation("/just/some/place/far/away/C/inside_the_number!/hey", "null");
+    default.cache.Write(
+        __().json.Pointer(P("/just/some/place/far/away/D/7/hey")),
+        __().box.int(-345));
+    CheckLocation("/just/some/place/far/away/D", "[]");
+    CheckLocation("/just/some/place/far/away/D/7/hey", "-345");
+    default.cache.Write(
+        __().json.Pointer(
+            P("/just/some/place/far/away/D/inside_the_array!/hey")),
+        __().box.float(1.1));
+    CheckLocation("/just/some/place/far/away/D/inside_the_array!/hey", "null");
+    CheckLocation("/just/some/place/far/away/D", "[]");
+    default.cache.Write(
+        __().json.Pointer(P("/just/some/place/far/away/D/-")),
+        __().box.bool(true));
+    CheckLocation("/just/some/place/far/away/D", "[true]");
+    default.cache.Write(
+        __().json.Pointer(P("/just/some/place/far/away/D/7")),
+        __().box.bool(true));
+    CheckLocation(
+        "/just/some/place/far/away/D",
+        "[true,null,null,null,null,null,null,true]");
+    Issue("Writing at the end of a JSON array several times doesn't correctly"
+        @ "keep all values.");
+    default.cache.Write(
+        __().json.Pointer(P("/just/some/place/far/away/D/-")),
+        __().box.int(13524));
+    default.cache.Write(
+        __().json.Pointer(P("/just/some/place/far/away/D/-")), none);
+    default.cache.Write(
+        __().json.Pointer(P("/just/some/place/far/away/D/-")),
+        __().box.int(121));
+    CheckLocation(
+        "/just/some/place/far/away/D",
+        "[true,null,null,null,null,null,null,true,13524,null,121]");
+}
+
+protected static function Test_DBCache_AllOperations_DuringLoading()
+{
+    local AcediaObject  complexData;
+    local ArrayList     newArrayData;
+
+    newArrayData = __().collections.EmptyArrayList();
+    newArrayData = newArrayData.AddInt(45);
+    newArrayData = newArrayData.AddItem(none);
+    newArrayData = newArrayData.AddString("lol");
+
+    Issue("Increment/remove/read sequence not working correctly.");
+    default.cache = DBCache(__().memory.Allocate(class'DBCache'));
+    complexData = MakeTestJSONObject();
+    default.cache.Increment(__().json.Pointer(P("")), complexData);
+    default.cache.Increment(__().json.Pointer(P("/B/A/1/A")),
+        __().text.FromString("oi"));
+    default.cache.Remove(__().json.Pointer(P("/B/A/1/B")));
+    default.cache.Remove(__().json.Pointer(P("/B/A/1/")));
+    default.cache.Increment(__().json.Pointer(P("/B/A")), newArrayData);
+    default.cache.Increment(__().json.Pointer(P("/C")), __().box.float(34.5));
+    default.cache.Increment(__().json.Pointer(P("/C")), __().box.bool(true));
+    default.cache.Increment(__().json.Pointer(P("/D")), newArrayData);
+    default.cache.Increment(__().json.Pointer(P("/D")), newArrayData);
+    default.cache.Increment(__().json.Pointer(P("/D")), newArrayData);
+    default.cache.Increment(__().json.Pointer(P("/B/A/1/A")),
+        __().text.FromString("! Yeah!"));
+    //  Override all increments!
+    default.cache.Write(__().json.Pointer(P("/D")), newArrayData);
+    CheckLocation("/B/A/1/A", "simpleValueoi! Yeah!");
+    CheckLocation("/B/A",
+        "[true,{\"A\":\"simpleValueoi! Yeah!\"},\"huh\",45,null,\"lol\"]");
+    CheckLocation("/C", "29.5");
+    CheckLocation("/D", "[45,null,\"lol\"]");
+}
+
+protected static function Test_DBCache_ApplyingPendingEdits()
+{
+    SubTest_DBCache_ApplyingPendingEdits_Simple();
+    SubTest_DBCache_ApplyingPendingEdits_Complex();
+}
+
+protected static function SubTest_DBCache_ApplyingPendingEdits_Simple()
+{
+    local int                           i;
+    local array<DBCache.PendingEdit>   result;
+
+    Issue("Pending writes successfully apply in simple JSON object case.");
+    default.cache = DBCache(__().memory.Allocate(class'DBCache'));
+    default.cache.Write(
+        __().json.Pointer(P("")),
+        __().collections.EmptyHashTable());
+    default.cache.Write(__().json.Pointer(P("/hey")), __().box.int(476));
+    default.cache.Write(__().json.Pointer(P("/hope")), none);
+    default.cache.Write(__().json.Pointer(P("/-")), __().ref.float(324.3));
+    result = default.cache.SetRealData(__().text.FromString("woah"));
+    for (i = 0; i < result.length; i += 1) {
+        TEST_ExpectTrue(result[i].successful);
+    }
+    CheckLocation("/hey", "476");
+    CheckLocation("/hope", "null");
+    CheckLocation("/-", "324.3");
+
+    Issue("Pending don't fail in a simple case of writing into JSON string.");
+    default.cache = DBCache(__().memory.Allocate(class'DBCache'));
+    default.cache.Write(__().json.Pointer(P("/hey")), __().box.int(476));
+    default.cache.Write(__().json.Pointer(P("/hope")), none);
+    default.cache.Write(__().json.Pointer(P("/-")), __().ref.float(324.3));
+    result = default.cache.SetRealData(__().text.FromString("woah"));
+    for (i = 0; i < result.length; i += 1) {
+        TEST_ExpectFalse(result[i].successful);
+    }
+    CheckLocation("/hey", "null");
+    CheckLocation("/hope", "null");
+    CheckLocation("/-", "null");
+}
+
+protected static function SubTest_DBCache_ApplyingPendingEdits_Complex()
+{
+    local array<DBCache.PendingEdit> result;
+
+    Issue("Pending writes incorrectly apply in complex case.");
+    default.cache = DBCache(__().memory.Allocate(class'DBCache'));
+    default.cache.Write(__().json.Pointer(P("/B/A/1/B")), __().box.int(777));
+    default.cache.Write(__().json.Pointer(P("/B/A/-")), __().box.bool(true));
+    default.cache.Write(__().json.Pointer(P("/D/5")), __().box.float(1.1));
+    default.cache.Write(
+        __().json.Pointer(P("/new")),
+        __().collections.EmptyHashTable());
+    default.cache.Write(
+        __().json.Pointer(P("/new/sub")),
+        __().text.FromString("!SubString!"));
+    default.cache.Write(
+        __().json.Pointer(P("/D/impossiburu")),
+        __().text.FromString("!SubString!"));
+    result = default.cache.SetRealData(MakeTestJSONObject());
+    CheckLocation("/B/A/1/B", "777");
+    CheckLocation("/B/A/3", "true");
+    CheckLocation("/D/5", "1.1");
+    CheckLocation("/D/2", "null");
+    CheckLocation("/new", "{\"sub\":\"!SubString!\"}");
+    TEST_ExpectTrue(result[0].successful);
+    TEST_ExpectTrue(result[1].successful);
+    TEST_ExpectTrue(result[2].successful);
+    TEST_ExpectTrue(result[3].successful);
+    TEST_ExpectTrue(result[4].successful);
+    TEST_ExpectFalse(result[5].successful);
+}
+
+protected static function Test_DBCache_ApplyingPendingEdit_AllOperations()
+{
+    local ArrayList                     newArrayData;
+    local array<DBCache.PendingEdit>    result;
+
+    newArrayData = __().collections.EmptyArrayList();
+    newArrayData = newArrayData.AddInt(45).AddItem(none).AddString("lol");
+
+    Issue("Pending increments and removals incorrectly apply in complex case.");
+    default.cache = DBCache(__().memory.Allocate(class'DBCache'));
+    default.cache.Increment(__().json.Pointer(P("/B/A/1/A")),
+        __().text.FromString("oi"));
+    default.cache.Remove(__().json.Pointer(P("/B/A/1/B")));
+    default.cache.Remove(__().json.Pointer(P("/B/A/1/")));
+    default.cache.Increment(__().json.Pointer(P("/B/A")), newArrayData);
+    default.cache.Increment(__().json.Pointer(P("/C")), __().box.float(34.5));
+    default.cache.Increment(__().json.Pointer(P("/C")), __().box.bool(true));
+    default.cache.Increment(__().json.Pointer(P("/D")), newArrayData);
+    default.cache.Increment(__().json.Pointer(P("/D")), newArrayData);
+    default.cache.Remove(__().json.Pointer(P("/B/A/Y")));
+    default.cache.Increment(__().json.Pointer(P("/B/A/1/A")),
+        __().text.FromString("! Yeah!"));
+    default.cache.Write(__().json.Pointer(P("/D")), newArrayData);
+    result = default.cache.SetRealData(MakeTestJSONObject());
+    TEST_ExpectTrue(result.length == 9);
+    TEST_ExpectTrue(result[0].successful);
+    TEST_ExpectTrue(result[1].successful);
+    TEST_ExpectTrue(result[2].successful);
+    TEST_ExpectTrue(result[3].successful);
+    TEST_ExpectTrue(result[4].successful);
+    TEST_ExpectFalse(result[5].successful);
+    TEST_ExpectFalse(result[6].successful);
+    TEST_ExpectTrue(result[7].successful);
+    TEST_ExpectTrue(result[8].successful);
+}
+
+protected static function Test_DBCache_BasicWriteRead_AfterLoading()
+{
+    local AcediaObject complexData;
+
+    Issue("Simple write/read sequence not working.");
+    default.cache = DBCache(__().memory.Allocate(class'DBCache'));
+    complexData = MakeTestJSONObject();
+    TEST_ExpectTrue(default.cache.SetRealData(complexData).length == 0);
+    default.cache.Write(__().json.Pointer(P("/B/A/1/B")), __().box.int(777));
+    default.cache.Write(__().json.Pointer(P("/B/A/-")), __().box.bool(true));
+    default.cache.Write(__().json.Pointer(P("/D/5")), __().box.float(1.1));
+    default.cache.Write(
+        __().json.Pointer(P("/new")),
+        __().collections.EmptyHashTable());
+    default.cache.Write(
+        __().json.Pointer(P("/new/sub")),
+        __().text.FromString("!SubString!"));
+    default.cache.Write(
+        __().json.Pointer(P("/D/impossiburu")),
+        __().text.FromString("!SubString!"));
+    CheckLocation("/B/A/1/B", "777");
+    CheckLocation("/B/A/3", "true");
+    CheckLocation("/D/5", "1.1");
+    CheckLocation("/new", "{\"sub\":\"!SubString!\"}");
+
+    Issue("Simple write/read are affecting data when they shouldn't.");
+    CheckLocation("/D/2", "null");
+    default.cache.Write(__().json.Pointer(P("")), __().box.float(1.1));
+    default.cache.Write(__().json.Pointer(P("/hm?")), __().box.float(2.2));
+    CheckLocation("", "1.1");
+}
+
+protected static function Test_DBCache_AllOperations_AfterLoading()
+{
+    local ArrayList newArrayData;
+
+    newArrayData = __().collections.EmptyArrayList();
+    newArrayData = newArrayData.AddInt(45).AddItem(none).AddString("lol");
+
+    Issue("Increment/remove/read sequence not working correctly.");
+    default.cache = DBCache(__().memory.Allocate(class'DBCache'));
+    default.cache.SetRealData(MakeTestJSONObject());
+    TEST_ExpectTrue(default.cache.Increment(__().json.Pointer(P("/B/A/1/A")),
+        __().text.FromString("oi")));
+    TEST_ExpectTrue(default.cache.Remove(__().json.Pointer(P("/B/A/1/B"))));
+    TEST_ExpectTrue(default.cache.Remove(__().json.Pointer(P("/B/A/1/"))));
+    TEST_ExpectTrue(default.cache.Increment(__().json.Pointer(P("/B/A")),
+        newArrayData));
+    TEST_ExpectTrue(default.cache.Increment(__().json.Pointer(P("/C")),
+        __().box.float(34.5)));
+    TEST_ExpectFalse(default.cache.Increment(__().json.Pointer(P("/C")),
+        __().box.bool(true)));
+    TEST_ExpectTrue(default.cache.Increment(__().json.Pointer(P("/D")),
+        newArrayData));
+    TEST_ExpectTrue(default.cache.Increment(__().json.Pointer(P("/D")),
+        newArrayData));
+    TEST_ExpectFalse(default.cache.Remove(__().json.Pointer(P("/B/A/Y"))));
+    TEST_ExpectTrue(default.cache.Increment(__().json.Pointer(P("/B/A/1/A")),
+        __().text.FromString("! Yeah!")));
+    default.cache.Write(__().json.Pointer(P("/D")), newArrayData);
+    CheckLocation("/B/A/1/A", "simpleValueoi! Yeah!");
+    CheckLocation("/B/A",
+        "[true,{\"A\":\"simpleValueoi! Yeah!\"},\"huh\",45,null,\"lol\"]");
+    CheckLocation("/C", "29.5");
+    CheckLocation("/D", "[45,null,\"lol\"]");
+}
+
+defaultproperties
+{
+    caseGroup   = "Database"
+    caseName    = "DBConnection related tests"
+}

sources/Data/Database/DBAPI.uc

@@ -55,7 +55,6 @@ public final function Database Load(BaseText databaseLink)
 {
     local Parser        parser;
     local Database      result;
-    local Text          immutableDatabaseName;
     local MutableText   databaseName;
 
     if (databaseLink == none) {
@@ -71,11 +70,9 @@ public final function Database Load(BaseText databaseLink)
         parser.FreeSelf();
         return none;
     }
-    immutableDatabaseName = databaseName.Copy();
+    result = LoadLocal(databaseName);
-    result = LoadLocal(immutableDatabaseName);
     parser.FreeSelf();
     databaseName.FreeSelf();
-    immutableDatabaseName.FreeSelf();
     return result;
 }
 
@@ -114,6 +111,56 @@ public final function JSONPointer GetPointer(BaseText databaseLink)
     return result;
 }
 
+/**
+ *  Opens a new `DBConnection` to the data referred to by the database link.
+ *
+ *  Opened `DBConnection` doesn't automatically start a connection, so you
+ *  need to call its `Connect()` method.
+ *
+ *  @param  databaseLink    Database link to the data we want to connect to.
+ *  @return Initialized `DBConnection` in case given link is valid and `none`
+ *      otherwise.
+ */
+public final function DBConnection OpenConnection(BaseText databaseLink)
+{
+    local DBConnection  result;
+    local Parser        parser;
+    local Database      databaseToConnect;
+    local JSONPointer   locationToConnect;
+    local MutableText   databaseName, textPointer;
+
+    if (databaseLink == none) {
+        return none;
+    }
+    parser = _.text.Parse(databaseLink);
+    //  Only local DBs are supported for now!
+    //  So just consume this prefix, if it's present.
+    parser.Match(P("[local]")).Confirm();
+    textPointer = parser
+        .R()
+        .MUntil(databaseName, _.text.GetCharacter(":"))
+        .MatchS(":")
+        .GetRemainderM();
+    if (parser.Ok())
+    {
+        databaseToConnect = LoadLocal(databaseName);
+        locationToConnect = _.json.Pointer(textPointer);
+        result = DBConnection(_.memory.Allocate(class'DBConnection'));
+        result.Initialize(databaseToConnect, locationToConnect);
+        _.memory.Free(databaseToConnect);
+        _.memory.Free(locationToConnect);
+    }
+    parser.FreeSelf();
+    _.memory.Free(databaseName);
+    _.memory.Free(textPointer);
+    if (result != none && !result.IsInitialized())
+    {
+        result.FreeSelf();
+        result = none;
+    }
+    return result;
+}
+
 /**
  *  Creates new local database with name `databaseName`.
  *
@@ -169,6 +216,7 @@ public final function LocalDatabaseInstance LoadLocal(BaseText databaseName)
     local Text                  rootRecordName;
     local LocalDatabase         newConfig;
     local LocalDatabaseInstance newLocalDBInstance;
+    local Text                  dbKey;
 
     if (databaseName == none) {
         return none;
@@ -189,7 +237,9 @@ public final function LocalDatabaseInstance LoadLocal(BaseText databaseName)
         return none;
     }
     newLocalDBInstance = LocalDatabaseInstance(_.memory.Allocate(localDBClass));
-    loadedLocalDatabases.SetItem(databaseName.Copy(), newLocalDBInstance);
+    dbKey = databaseName.Copy();
+    loadedLocalDatabases.SetItem(dbKey, newLocalDBInstance);
+    dbKey.FreeSelf();
     if (newConfig.HasDefinedRoot())
     {
         rootRecordName = newConfig.GetRootName();

sources/Data/Database/DBTask.uc

@@ -6,7 +6,7 @@
  *  completed and will self-destruct afterwards. Concrete delegates are
  *  declared in child classes of this `DBTask`, since they can have different
  *  signatures, depending on the query.
- *      Copyright 2021 Anton Tarasenko
+ *      Copyright 2021-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -54,6 +54,7 @@ var private int     previousTaskLifeVersion;
 
 var private Database.DBQueryResult  taskResult;
 var private bool                    isReadyToComplete;
+var private int                     requestID;
 
 var private LoggerAPI.Definition errLoopInTaskChain;
 
@@ -65,6 +66,18 @@ protected function Finalizer()
     previousTask            = none;
     previousTaskLifeVersion = -1;
     isReadyToComplete       = false;
+    requestID               = 0;
+}
+
+/**
+ *  Returns ID of the request set inside `SetResult()` for the caller `DBTask`.
+ *
+ *  @return ID of the request set inside `SetResult()` for the caller `DBTask`.
+ *      If `SetResult()` wasn't yet called returns `0`.
+ */
+protected function int GetRequestID()
+{
+    return requestID;
 }
 
 /**
@@ -105,12 +118,17 @@ public final function Database.DBQueryResult GetResult()
  *  This value can be assigned several times and the last assigned value will
  *  be used.
  *
- *  @param  result  Result of the query, relevant to the caller task.
+ *  @param  result      Result of the query, relevant to the caller task.
+ *  @param  requestID   ID of the request this task is responding to, specified
+ *      at the time request was made.
  */
-public final function SetResult(Database.DBQueryResult result)
+public final function SetResult(
+    Database.DBQueryResult  result,
+    optional int            completedRequestID)
 {
     taskResult          = result;
     isReadyToComplete   = true;
+    requestID           = completedRequestID;
 }
 
 /**

sources/Data/Database/Database.uc

@@ -7,7 +7,7 @@
  *      All of the methods are asynchronous - they do not return requested
  *  values immediately and instead require user to provide a handler function
  *  that will be called once operation is completed.
- *      Copyright 2021-2022 Anton Tarasenko
+ *      Copyright 2021-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -73,15 +73,27 @@ enum DBQueryResult
  *      to load data as immutable Acedia's types and `true` will make it load
  *      data as mutable types. This setting does not affect `Collection`s into
  *      which JSON arrays and objects are converted - they are always mutable.
+ *  @param  requestID       ID of this request. It will be reported when
+ *      database's task is completed. Can be used to correspond database's
+ *      responses with particular requests.
  *  @return Task object that corresponds to this `ReadData()` call.
  *      *   Guaranteed to be not `none`;
  *      *   Use it to connect a handler for when reading task is complete:
- *              `ReadData(...).connect = handler`,
+ *          `ReadData(...).connect = handler`,
- *              where `handler` must have the following signature:
+ *          where `handler` must have the following signature:
- *              `connect(DBQueryResult result, AcediaObject data)`;
+ *          ```
+ *          connect(
+ *              DBQueryResult       result,
+ *              take AcediaObject   data,
+ *              Database            source,
+ *              int                 requestID)`;
+ *          ```
  *      *   Ownership of `data` object returned in the `connect()` is considered
  *          to be transferred to whoever handled result of this query.
  *          It must be deallocated once no longer needed.
+ *      *   `source` provides reference to the database, whose data was
+ *          requested, `requestID` provides the same number as `requestID`
+ *          parameter of this method.
  *      *   Possible `DBQueryResult` types are `DBR_Success`,
  *          `DBR_InvalidPointer` and `DBR_InvalidDatabase`;
  *      *   `data` is guaranteed to be `none` if `result != DBR_Success`;
@@ -90,7 +102,8 @@ enum DBQueryResult
  */
 public function DBReadTask ReadData(
     JSONPointer     pointer,
-    optional bool   makeMutable)
+    optional bool   makeMutable,
+    optional int    requestID)
 {
     return none;
 }
@@ -110,12 +123,18 @@ public function DBReadTask ReadData(
  *  @param  data    Data that needs to be written at the specified location
  *      inside the database. For method to succeed this object needs to have
  *      JSON-compatible type (see `_.json.IsCompatible()` for more details).
+ *  @param  requestID       ID of this request. It will be reported when
+ *      database's task is completed. Can be used to correspond database's
+ *      responses with particular requests.
  *  @return Task object that corresponds to this `WriteData()` call.
  *      *   Guaranteed to be not `none`;
  *      *   Use it to connect a handler for when writing task is complete:
  *          `WriteData(...).connect = handler`,
  *          where `handler` must have the following signature:
- *          `connect(DBQueryResult result)`;
+ *          `connect(DBQueryResult result, Database source, int requestID)`;
+ *      *   `source` provides reference to the database, whose data was
+ *          requested, `requestID` provides the same number as `requestID`
+ *          parameter of this method.
  *      *   Possible `DBQueryResult` types are `DBR_Success`,
  *          `DBR_InvalidPointer`, `DBR_InvalidDatabase` and `DBR_InvalidData`;
  *      *   Data is actually written inside the database iff
@@ -128,7 +147,10 @@ public function DBReadTask ReadData(
  *          Example: writing data at "/sub-object/valueA" will always fail if
  *          "sub-object" does not exist.
  */
-public function DBWriteTask WriteData(JSONPointer pointer, AcediaObject data)
+public function DBWriteTask WriteData(
+    JSONPointer     pointer,
+    AcediaObject    data,
+    optional int    requestID)
 {
     return none;
 }
@@ -141,12 +163,18 @@ public function DBWriteTask WriteData(JSONPointer pointer, AcediaObject data)
  *
  *  @param  pointer JSON pointer to the location of the data to remove from
  *      database. `none` is always treated as an invalid JSON pointer.
+ *  @param  requestID       ID of this request. It will be reported when
+ *      database's task is completed. Can be used to correspond database's
+ *      responses with particular requests.
  *  @return Task object that corresponds to this `RemoveData()` call.
  *      *   Guaranteed to be not `none`;
  *      *   Use it to connect a handler for when writing task is complete:
  *          `RemoveData(...).connect = handler`,
  *          where `handler` must have the following signature:
- *          `connect(DBQueryResult result)`.
+ *          `connect(DBQueryResult result, Database source, int requestID)`.
+ *      *   `source` provides reference to the database, whose data was
+ *          requested, `requestID` provides the same number as `requestID`
+ *          parameter of this method.
  *      *   Possible `DBQueryResult` types are `DBR_Success`,
  *          `DBR_InvalidPointer` and `DBR_InvalidDatabase`;
  *      *   Data is actually removed from the database iff
@@ -154,7 +182,9 @@ public function DBWriteTask WriteData(JSONPointer pointer, AcediaObject data)
  *      *   `DBR_InvalidPointer` can be produced if either `pointer == none` or
  *          it does not point at any existing value inside the caller database.
  */
-public function DBRemoveTask RemoveData(JSONPointer pointer)
+public function DBRemoveTask RemoveData(
+    JSONPointer     pointer,
+    optional int    requestID)
 {
     return none;
 }
@@ -166,12 +196,24 @@ public function DBRemoveTask RemoveData(JSONPointer pointer)
  *  @param  pointer JSON pointer to the location of the data for which type
  *      needs to be checked.
  *      `none` is always treated as an invalid JSON pointer.
+ *  @param  requestID       ID of this request. It will be reported when
+ *      database's task is completed. Can be used to correspond database's
+ *      responses with particular requests.
  *  @return Task object that corresponds to this `CheckDataType()` call.
  *      *   Guaranteed to be not `none`;
  *      *   Use it to connect a handler for when reading task is complete:
  *          `CheckDataType(...).connect = handler`,
  *          where `handler` must have the following signature:
- *          `connect(DBQueryResult result, Database.DataType type)`;
+ *          ```
+ *          connect(
+ *              DBQueryResult       result,
+ *              Database.DataType   type,
+ *              Database            source,
+ *              int                 requestID)
+ *          ```
+ *      *   `source` provides reference to the database, whose data was
+ *          requested, `requestID` provides the same number as `requestID`
+ *          parameter of this method.
  *      *   Possible `DBQueryResult` types are `DBR_Success`,
  *          `DBR_InvalidPointer` and `DBR_InvalidDatabase`;
  *      *   This task can only fail if either caller database is broken
@@ -181,7 +223,9 @@ public function DBRemoveTask RemoveData(JSONPointer pointer)
  *      *   Data is actually removed from the database iff
  *          `result == DBR_Success`.
  */
-public function DBCheckTask CheckDataType(JSONPointer pointer)
+public function DBCheckTask CheckDataType(
+    JSONPointer     pointer,
+    optional int    requestID)
 {
     return none;
 }
@@ -197,12 +241,24 @@ public function DBCheckTask CheckDataType(JSONPointer pointer)
  *  @param  pointer JSON pointer to the location of the JSON object or array
  *      for which size needs to be obtained.
  *      `none` is always treated as an invalid JSON pointer.
+ *  @param  requestID       ID of this request. It will be reported when
+ *      database's task is completed. Can be used to correspond database's
+ *      responses with particular requests.
  *  @return Task object that corresponds to this `GetDataSize()` call.
  *      *   Guaranteed to be not `none`;
  *      *   Use it to connect a handler for when reading task is complete:
  *          `GetDataSize(...).connect = handler`,
  *          where `handler` must have the following signature:
- *          `connect(DBQueryResult result, int size)`.
+ *          ```
+ *          connect(
+ *              DBQueryResult   result,
+ *              int             size,
+ *              Database        source,
+ *              int             requestID)
+ *          ```
+ *      *   `source` provides reference to the database, whose data was
+ *          requested, `requestID` provides the same number as `requestID`
+ *          parameter of this method.
  *      *   Possible `DBQueryResult` types are `DBR_Success`,
  *          `DBR_InvalidPointer` and `DBR_InvalidDatabase`;
  *      *   Returned `size` value is actually a size of referred
@@ -211,7 +267,9 @@ public function DBCheckTask CheckDataType(JSONPointer pointer)
  *          it does not point at a JSON object or array inside the
  *          caller database.
  */
-public function DBSizeTask GetDataSize(JSONPointer pointer)
+public function DBSizeTask GetDataSize(
+    JSONPointer     pointer,
+    optional int    requestID)
 {
     return none;
 }
@@ -225,15 +283,27 @@ public function DBSizeTask GetDataSize(JSONPointer pointer)
  *  @param  pointer JSON pointer to the location of the JSON object for which
  *      keys need to be obtained.
  *      `none` is always treated as an invalid JSON pointer.
+ *  @param  requestID       ID of this request. It will be reported when
+ *      database's task is completed. Can be used to correspond database's
+ *      responses with particular requests.
  *  @return Task object that corresponds to this `GetDataKeys()` call.
  *      *   Guaranteed to be not `none`;
  *      *   Use it to connect a handler for when reading task is complete:
  *          `GetDataKeys(...).connect = handler`,
  *          where `handler` must have the following signature:
- *          `connect(DBQueryResult result, ArrayList keys)`.
+ *          ```
+ *          connect(
+ *              DBQueryResult   result,
+ *              take ArrayList  keys,
+ *              Database        source,
+ *              int             requestID)
+ *          ```
  *      *   Ownership of `keys` array returned in the `connect()` is considered
  *          to be transferred to whoever handled result of this query.
  *          It must be deallocated once no longer needed.
+ *      *   `source` provides reference to the database, whose data was
+ *          requested, `requestID` provides the same number as `requestID`
+ *          parameter of this method.
  *      *   Possible `DBQueryResult` types are `DBR_Success`,
  *          `DBR_InvalidPointer`, `DBR_InvalidData` and `DBR_InvalidDatabase`;
  *      *   Returned `keys` will be non-`none` and contain keys of the referred
@@ -243,7 +313,9 @@ public function DBSizeTask GetDataSize(JSONPointer pointer)
  *          point at a JSON object inside caller database
  *          (value can either not exist at all or have some other type).
  */
-public function DBKeysTask GetDataKeys(JSONPointer pointer)
+public function DBKeysTask GetDataKeys(
+    JSONPointer     pointer,
+    optional int    requestID)
 {
     return none;
 }
@@ -255,19 +327,21 @@ public function DBKeysTask GetDataKeys(JSONPointer pointer)
  *  "Incrementing" is an operation that is safe from the point of view of
  *  simultaneous access. What "incrementing" actually does depends on
  *  the passed JSON value (`increment` parameter):
- *      (0.  Unless `pointer` points at the JSON null value - then "increment"
+ *
- *          acts as a `WriteData()` method regardless of `increment`'s value);
+ *      (0. ...unless `pointer` points at the JSON null or missing value (within
+ *          existing container - then "increment" acts as a `WriteData()` method
+ *          regardless of `increment`'s value;)
  *      1.  JSON null: it never modifies existing value and reports an error if
  *          existing value was not itself JSON null;
- *      2.  JSON bool: if combines with stored JSON bool value -
+ *      2.  JSON bool: if combined with stored JSON bool value -
  *          performs logical "or" operation. Otherwise fails;
- *      3. JSON number: if combines with stored JSON numeric value -
+ *      3.  JSON number: if combined with stored JSON numeric value -
  *          adds values together. Otherwise fails.
- *      4. JSON string: if combines with stored JSON string value -
+ *      4.  JSON string: if combined with stored JSON string value -
  *          concatenates itself at the end. Otherwise fails.
- *      5. JSON array: if combines with stored JSON array value -
+ *      5.  JSON array: if combined with stored JSON array value -
  *          concatenates itself at the end. Otherwise fails.
- *      6. JSON object: if combines with stored JSON object value -
+ *      6.  JSON object: if combined with stored JSON object value -
  *          `increment` adds it's own values with new keys into the stored
  *          JSON object. Does not override old values.
  *          Fails when combined with any other type.
@@ -280,12 +354,18 @@ public function DBKeysTask GetDataKeys(JSONPointer pointer)
  *      with `increment` parameter.
  *  @param  increment   JSON-compatible value to be used as an increment for
  *      the data at the specified location inside the database.
+ *  @param  requestID       ID of this request. It will be reported when
+ *      database's task is completed. Can be used to correspond database's
+ *      responses with particular requests.
  *  @return Task object that corresponds to this `IncrementData()` call.
  *      *   Guaranteed to be not `none`;
  *      *   Use it to connect a handler for when reading task is complete:
  *          `IncrementData(...).connect = handler`,
  *          where `handler` must have the following signature:
- *          `connect(DBQueryResult result)`.
+ *          `connect(DBQueryResult result, Database source, int requestID)`.
+ *      *   `source` provides reference to the database, whose data was
+ *          requested, `requestID` provides the same number as `requestID`
+ *          parameter of this method.
  *      *   Possible `DBQueryResult` types are `DBR_Success`,
  *          `DBR_InvalidPointer`, `DBR_InvalidData` and `DBR_InvalidDatabase`;
  *      *   Data is actually incremented iff `result == DBR_Success`;
@@ -299,7 +379,8 @@ public function DBKeysTask GetDataKeys(JSONPointer pointer)
  */
 public function DBIncrementTask IncrementData(
     JSONPointer     pointer,
-    AcediaObject    increment)
+    AcediaObject    increment,
+    optional int    requestID)
 {
     return none;
 }

sources/Data/Database/Local/DBRecord.uc

@@ -184,6 +184,7 @@ private final function DBRecordPointer MakeRecordPointer(
     return pointer;
 }
 
+//  Converts `JSONPointer` into our internal representation.
 private final function DBRecordPointer ConvertPointer(JSONPointer jsonPointer)
 {
     if (jsonPointer == none) {
@@ -192,6 +193,8 @@ private final function DBRecordPointer ConvertPointer(JSONPointer jsonPointer)
     return ConvertPointerPath(jsonPointer, 0, jsonPointer.GetLength());
 }
 
+//  Produced out internal pointer representation `DBRecordPointer` to
+//  the container that stores object, referred to by a given `JSONPointer`.
 private final function DBRecordPointer ConvertContainerPointer(
     JSONPointer jsonPointer)
 {

sources/Data/Database/Local/LocalDatabaseInstance.uc

@@ -149,54 +149,61 @@ private final function DBTask MakeNewTask(class<DBTask> newTaskClass)
     return newTask;
 }
 
-private function bool ValidatePointer(JSONPointer pointer, DBTask relevantTask)
+private function bool ValidatePointer(
+    JSONPointer pointer,
+    DBTask      relevantTask,
+    int         requestID)
 {
     if (pointer != none) {
         return true;
     }
-    relevantTask.SetResult(DBR_InvalidPointer);
+    relevantTask.SetResult(DBR_InvalidPointer, requestID);
     return false;
 }
 
-private function bool ValidateRootRecord(DBTask relevantTask)
+private function bool ValidateRootRecord(DBTask relevantTask, int requestID)
 {
     if (rootRecord != none) {
         return true;
     }
-    relevantTask.SetResult(DBR_InvalidDatabase);
+    relevantTask.SetResult(DBR_InvalidDatabase, requestID);
     return false;
 }
 
 public function DBReadTask ReadData(
     JSONPointer     pointer,
-    optional bool   makeMutable)
+    optional bool   makeMutable,
+    optional int    requestID)
 {
     local AcediaObject  queryResult;
     local DBReadTask    readTask;
     readTask = DBReadTask(MakeNewTask(class'DBReadTask'));
-    if (!ValidatePointer(pointer, readTask))    return readTask;
+    if (!ValidatePointer(pointer, readTask, requestID)) return readTask;
-    if (!ValidateRootRecord(readTask))          return readTask;
+    if (!ValidateRootRecord(readTask, requestID))       return readTask;
 
     if (rootRecord.LoadObject(pointer, queryResult, makeMutable))
     {
         readTask.SetReadData(queryResult);
-        readTask.SetResult(DBR_Success);
+        readTask.SetResult(DBR_Success, requestID);
     }
     else
     {
-        readTask.SetResult(DBR_InvalidPointer);
+        readTask.SetResult(DBR_InvalidPointer, requestID);
         _.memory.Free(queryResult); //  just in case
     }
     return readTask;
 }
 
-public function DBWriteTask WriteData(JSONPointer pointer, AcediaObject data)
+public function DBWriteTask WriteData(
+    JSONPointer     pointer,
+    AcediaObject    data,
+    optional int    requestID)
 {
     local bool          isDataStorable;
     local DBWriteTask   writeTask;
     writeTask = DBWriteTask(MakeNewTask(class'DBWriteTask'));
-    if (!ValidatePointer(pointer, writeTask))   return writeTask;
+    if (!ValidatePointer(pointer, writeTask, requestID))    return writeTask;
-    if (!ValidateRootRecord(writeTask))         return writeTask;
+    if (!ValidateRootRecord(writeTask, requestID))          return writeTask;
 
     //  We can only write JSON array as the root value
     if (data != none && pointer.GetLength() <= 0) {
@@ -207,99 +214,111 @@ public function DBWriteTask WriteData(JSONPointer pointer, AcediaObject data)
     }
     if (!isDataStorable)
     {
-        writeTask.SetResult(DBR_InvalidData);
+        writeTask.SetResult(DBR_InvalidData, requestID);
         return writeTask;
     }
     if (rootRecord.SaveObject(pointer, data))
     {
-        writeTask.SetResult(DBR_Success);
+        writeTask.SetResult(DBR_Success, requestID);
         ScheduleDiskUpdate();
     }
     else {
-        writeTask.SetResult(DBR_InvalidPointer);
+        writeTask.SetResult(DBR_InvalidPointer, requestID);
     }
     return writeTask;
 }
 
-public function DBRemoveTask RemoveData(JSONPointer pointer)
+public function DBRemoveTask RemoveData(
+    JSONPointer     pointer,
+    optional int    requestID)
 {
     local DBRemoveTask removeTask;
     removeTask = DBRemoveTask(MakeNewTask(class'DBRemoveTask'));
-    if (!ValidatePointer(pointer, removeTask))  return removeTask;
+    if (!ValidatePointer(pointer, removeTask, requestID))   return removeTask;
-    if (!ValidateRootRecord(removeTask))        return removeTask;
+    if (!ValidateRootRecord(removeTask, requestID))         return removeTask;
 
     if (pointer.GetLength() == 0)
     {
         rootRecord.EmptySelf();
-        removeTask.SetResult(DBR_Success);
+        removeTask.SetResult(DBR_Success, requestID);
         return removeTask;
     }
     if (rootRecord.RemoveObject(pointer))
     {
-        removeTask.SetResult(DBR_Success);
+        removeTask.SetResult(DBR_Success, requestID);
         ScheduleDiskUpdate();
     }
     else {
-        removeTask.SetResult(DBR_InvalidPointer);
+        removeTask.SetResult(DBR_InvalidPointer, requestID);
     }
     return removeTask;
 }
 
-public function DBCheckTask CheckDataType(JSONPointer pointer)
+public function DBCheckTask CheckDataType(
+    JSONPointer     pointer,
+    optional int    requestID)
 {
     local DBCheckTask checkTask;
     checkTask = DBCheckTask(MakeNewTask(class'DBCheckTask'));
-    if (!ValidatePointer(pointer, checkTask))   return checkTask;
+    if (!ValidatePointer(pointer, checkTask, requestID))    return checkTask;
-    if (!ValidateRootRecord(checkTask))         return checkTask;
+    if (!ValidateRootRecord(checkTask, requestID))          return checkTask;
 
     checkTask.SetDataType(rootRecord.GetObjectType(pointer));
-    checkTask.SetResult(DBR_Success);
+    checkTask.SetResult(DBR_Success, requestID);
     return checkTask;
 }
 
-public function DBSizeTask GetDataSize(JSONPointer pointer)
+public function DBSizeTask GetDataSize(
+    JSONPointer     pointer,
+    optional int    requestID)
 {
     local DBSizeTask sizeTask;
     sizeTask = DBSizeTask(MakeNewTask(class'DBSizeTask'));
-    if (!ValidatePointer(pointer, sizeTask))    return sizeTask;
+    if (!ValidatePointer(pointer, sizeTask, requestID)) return sizeTask;
-    if (!ValidateRootRecord(sizeTask))          return sizeTask;
+    if (!ValidateRootRecord(sizeTask, requestID))       return sizeTask;
 
     sizeTask.SetDataSize(rootRecord.GetObjectSize(pointer));
-    sizeTask.SetResult(DBR_Success);
+    sizeTask.SetResult(DBR_Success, requestID);
     return sizeTask;
 }
 
-public function DBKeysTask GetDataKeys(JSONPointer pointer)
+public function DBKeysTask GetDataKeys(
+    JSONPointer     pointer,
+    optional int    requestID)
 {
     local ArrayList     keys;
     local DBKeysTask    keysTask;
     keysTask = DBKeysTask(MakeNewTask(class'DBKeysTask'));
-    if (!ValidatePointer(pointer, keysTask))    return keysTask;
+    if (!ValidatePointer(pointer, keysTask, requestID)) return keysTask;
-    if (!ValidateRootRecord(keysTask))          return keysTask;
+    if (!ValidateRootRecord(keysTask, requestID))       return keysTask;
 
     keys = rootRecord.GetObjectKeys(pointer);
     keysTask.SetDataKeys(keys);
     if (keys == none) {
-        keysTask.SetResult(DBR_InvalidData);
+        keysTask.SetResult(DBR_InvalidData, requestID);
     }
     else {
-        keysTask.SetResult(DBR_Success);
+        keysTask.SetResult(DBR_Success, requestID);
     }
     return keysTask;
 }
 
 public function DBIncrementTask IncrementData(
     JSONPointer     pointer,
-    AcediaObject    increment)
+    AcediaObject    increment,
+    optional int    requestID)
 {
     local DBQueryResult     queryResult;
     local DBIncrementTask   incrementTask;
     incrementTask = DBIncrementTask(MakeNewTask(class'DBIncrementTask'));
-    if (!ValidatePointer(pointer, incrementTask))   return incrementTask;
+    if (!ValidatePointer(pointer, incrementTask, requestID)) {
-    if (!ValidateRootRecord(incrementTask))         return incrementTask;
+        return incrementTask;
-
+    }
+    if (!ValidateRootRecord(incrementTask, requestID)) {
+        return incrementTask;
+    }
     queryResult = rootRecord.IncrementObject(pointer, increment);
-    incrementTask.SetResult(queryResult);
+    incrementTask.SetResult(queryResult, requestID);
     if (queryResult == DBR_Success) {
         ScheduleDiskUpdate();
     }

sources/Data/Database/Tasks/DBCheckTask.uc

@@ -1,6 +1,6 @@
 /**
  *  Variant of `DBTask` for `CheckDataType()` query.
- *      Copyright 2021 Anton Tarasenko
+ *      Copyright 2021-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -24,7 +24,8 @@ var private Database.DataType queryTypeResponse;
 delegate connect(
     Database.DBQueryResult  result,
     Database.DataType       type,
-    Database                source) {}
+    Database                source,
+    int                     requestID) {}
 
 protected function Finalizer()
 {
@@ -40,7 +41,7 @@ public function SetDataType(Database.DataType type)
 
 protected function CompleteSelf(Database source)
 {
-    connect(GetResult(), queryTypeResponse, source);
+    connect(GetResult(), queryTypeResponse, source, GetRequestID());
 }
 
 defaultproperties

sources/Data/Database/Tasks/DBIncrementTask.uc

@@ -1,6 +1,6 @@
 /**
  *  Variant of `DBTask` for `IncrementData()` query.
- *      Copyright 2021 Anton Tarasenko
+ *      Copyright 2021-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -19,7 +19,10 @@
  */
 class DBIncrementTask extends DBTask;
 
-delegate connect(Database.DBQueryResult result, Database source) {}
+delegate connect(
+    Database.DBQueryResult  result,
+    Database                source,
+    int                     requestID) {}
 
 protected function Finalizer()
 {
@@ -29,7 +32,7 @@ protected function Finalizer()
 
 protected function CompleteSelf(Database source)
 {
-    connect(GetResult(), source);
+    connect(GetResult(), source, GetRequestID());
 }
 
 defaultproperties

sources/Data/Database/Tasks/DBKeysTask.uc

@@ -1,6 +1,6 @@
 /**
  *  Variant of `DBTask` for `GetDataKeys()` query.
- *      Copyright 2021-2022 Anton Tarasenko
+ *      Copyright 2021-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -23,8 +23,9 @@ var private ArrayList queryKeysResponse;
 
 delegate connect(
     Database.DBQueryResult  result,
-    ArrayList               keys,
+    /*take*/ ArrayList      keys,
-    Database                source) {}
+    Database                source,
+    int                     requestID) {}
 
 protected function Finalizer()
 {
@@ -40,7 +41,7 @@ public function SetDataKeys(/* take */ ArrayList keys)
 
 protected function CompleteSelf(Database source)
 {
-    connect(GetResult(), queryKeysResponse, source);
+    connect(GetResult(), queryKeysResponse, source, GetRequestID());
 }
 
 defaultproperties

sources/Data/Database/Tasks/DBReadTask.uc

@@ -1,6 +1,6 @@
 /**
  *  Variant of `DBTask` for `ReadData()` query.
- *      Copyright 2021 Anton Tarasenko
+ *      Copyright 2021-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -23,8 +23,9 @@ var private AcediaObject queryDataResponse;
 
 delegate connect(
     Database.DBQueryResult  result,
-    AcediaObject            data,
+    /*take*/ AcediaObject   data,
-    Database                source) {}
+    Database                source,
+    int                     requestID) {}
 
 protected function Finalizer()
 {
@@ -40,7 +41,7 @@ public function SetReadData(AcediaObject data)
 
 protected function CompleteSelf(Database source)
 {
-    connect(GetResult(), queryDataResponse, source);
+    connect(GetResult(), queryDataResponse, source, GetRequestID());
 }
 
 defaultproperties

sources/Data/Database/Tasks/DBRemoveTask.uc

@@ -1,6 +1,6 @@
 /**
  *  Variant of `DBTask` for `RemoveData()` query.
- *      Copyright 2021 Anton Tarasenko
+ *      Copyright 2021-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -19,7 +19,10 @@
  */
 class DBRemoveTask extends DBTask;
 
-delegate connect(Database.DBQueryResult result, Database source) {}
+delegate connect(
+    Database.DBQueryResult  result,
+    Database                source,
+    int                     requestID) {}
 
 protected function Finalizer()
 {
@@ -29,7 +32,7 @@ protected function Finalizer()
 
 protected function CompleteSelf(Database source)
 {
-    connect(GetResult(), source);
+    connect(GetResult(), source, GetRequestID());
 }
 
 defaultproperties

sources/Data/Database/Tasks/DBSizeTask.uc

@@ -1,6 +1,6 @@
 /**
  *  Variant of `DBTask` for `GetDataSize()` query.
- *      Copyright 2021 Anton Tarasenko
+ *      Copyright 2021-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -21,7 +21,11 @@ class DBSizeTask extends DBTask;
 
 var private int querySizeResponse;
 
-delegate connect(Database.DBQueryResult result, int size, Database source) {}
+delegate connect(
+    Database.DBQueryResult  result,
+    int                     size,
+    Database                source,
+    int                     requestID) {}
 
 protected function Finalizer()
 {
@@ -37,7 +41,7 @@ public function SetDataSize(int size)
 
 protected function CompleteSelf(Database source)
 {
-    connect(GetResult(), querySizeResponse, source);
+    connect(GetResult(), querySizeResponse, source, GetRequestID());
 }
 
 defaultproperties

sources/Data/Database/Tasks/DBWriteTask.uc

@@ -1,6 +1,6 @@
 /**
  *  Variant of `DBTask` for `WriteData()` query.
- *      Copyright 2021 Anton Tarasenko
+ *      Copyright 2021-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -19,7 +19,10 @@
  */
 class DBWriteTask extends DBTask;
 
-delegate connect(Database.DBQueryResult result, Database source) {}
+delegate connect(
+    Database.DBQueryResult  result,
+    Database                source,
+    int                     requestID) {}
 
 protected function Finalizer()
 {
@@ -29,7 +32,7 @@ protected function Finalizer()
 
 protected function CompleteSelf(Database source)
 {
-    connect(GetResult(), source);
+    connect(GetResult(), source, GetRequestID());
 }
 
 defaultproperties

sources/Data/Database/Tests/TEST_LocalDatabase.uc

@@ -27,63 +27,78 @@ var protected Database.DBQueryResult    resultType;
 var protected Database.DataType         resultDataType;
 var protected HashTable                 resultData;
 var protected AcediaObject              resultObject;
+var protected int                       resultRequestID;
 
 protected function DBReadingHandler(
     Database.DBQueryResult  result,
     AcediaObject            data,
-    Database                source)
+    Database                source,
+    int                     requestID)
 {
     default.resultType      = result;
     default.resultObject    = data;
     default.resultData      = HashTable(data);
+    default.resultRequestID = requestID;
 }
 
 protected function DBKeysHandler(
     Database.DBQueryResult  result,
     ArrayList               keys,
-    Database                source)
+    Database                source,
+    int                     requestID)
 {
-    default.resultType = result;
+    default.resultType      = result;
-    default.resultKeys = keys;
+    default.resultKeys      = keys;
+    default.resultRequestID = requestID;
 }
 
 protected function DBCheckHandler(
     Database.DBQueryResult  result,
     Database.DataType       type,
-    Database                source)
+    Database                source,
+    int                     requestID)
 {
-    default.resultType = result;
+    default.resultType      = result;
-    default.resultDataType = type;
+    default.resultDataType  = type;
+    default.resultRequestID = requestID;
 }
 
 protected function DBSizeHandler(
     Database.DBQueryResult  result,
     int                     size,
-    Database                source)
+    Database                source,
+    int                     requestID)
 {
-    default.resultType = result;
+    default.resultType      = result;
-    default.resultSize = size;
+    default.resultSize      = size;
+    default.resultRequestID = requestID;
 }
 
 protected function DBWritingHandler(
     Database.DBQueryResult  result,
-    Database                source)
+    Database                source,
+    int                     requestID)
 {
-    default.resultType = result;
+    default.resultType      = result;
+    default.resultRequestID = requestID;
 }
 
 protected function DBIncrementHandler(
     Database.DBQueryResult  result,
-    Database                source)
+    Database                source,
+    int                     requestID)
 {
-    default.resultType = result;
+    default.resultType      = result;
+    default.resultRequestID = requestID;
 }
 
 protected function DBRemoveHandler(
     Database.DBQueryResult  result,
-    Database                source)
+    Database                source,
+    int                     requestID)
 {
-    default.resultType = result;
+    default.resultType      = result;
+    default.resultRequestID = requestID;
 }
 
 protected static function ReadFromDB(LocalDatabaseInstance db, string pointer)
@@ -220,6 +235,7 @@ protected static function TESTS()
     Test_TaskChaining();
     Test_Removal();
     Test_Increment();
+    Test_RequestID();
 }
 
 protected static function Test_LoadingPrepared()
@@ -1232,8 +1248,9 @@ protected static function SubTest_IncrementRewriteArray(
 
 protected static function SubTest_IncrementMissing(LocalDatabaseInstance db)
 {
-    local DBIncrementTask task;
+    local DBIncrementTask   task;
-    Issue("New values are created in database after incrementing with path"
+    local DBCheckTask       checkTask;
+    Issue("New values are not created in database after incrementing with path"
         @ "pointing to non-existing value.");
     task = db.IncrementData(__().json.Pointer(P("/L")), __().box.int(345));
     task.connect = DBIncrementHandler;
@@ -1245,13 +1262,168 @@ protected static function SubTest_IncrementMissing(LocalDatabaseInstance db)
     task.connect = DBIncrementHandler;
     task.TryCompleting();
     TEST_ExpectTrue(default.resultType == DBR_Success);
-    db.CheckDataType(__().json.Pointer(P("/L"))).connect = DBCheckHandler;
+    checkTask = db.CheckDataType(__().json.Pointer(P("/L")));
+    checkTask.connect = DBCheckHandler;
+    checkTask.TryCompleting();
+    TEST_ExpectTrue(default.resultDataType == JSON_Number);
+    TEST_ExpectTrue(default.resultType == DBR_Success);
     ReadFromDB(db, "/B/A/1/");
     TEST_ExpectTrue(default.resultDataType == JSON_Number);
     TEST_ExpectTrue(ArrayList(default.resultObject).GetLength() == 12);
     TEST_ExpectTrue(ArrayList(default.resultObject).GetInt(11) == 85);
 }
 
+protected static function Test_RequestID()
+{
+    local LocalDatabaseInstance db;
+    local ArrayList             templateArray;
+    local HashTable             templateObject;
+    templateObject = GetJSONSubTemplateObject();
+    templateArray = GetJSONSubTemplateArray();
+    db = __core().db.NewLocal(P("TEST_DB"));
+    db.WriteData(__().json.Pointer(P("")), templateObject);
+    db.WriteData(__().json.Pointer(P("/B")), templateObject);
+    db.WriteData(__().json.Pointer(P("/C")), __().box.int(-5));
+    db.WriteData(__().json.Pointer(P("/D")), __().box.bool(false));
+    db.WriteData(__().json.Pointer(P("/B/A")), templateArray);
+    db.WriteData(__().json.Pointer(P("/B/A/1")), templateObject);
+    db.WriteData(__().json.Pointer(P("/B/A/1/")), templateArray);
+    /* `db` now contains:
+    {
+        "A": "simpleValue",
+        "B": {
+            "A": [true, {
+                "A": "simpleValue",
+                "B": 11.12,
+                "": [true, null, "huh"]
+            }, "huh"],
+            "B": 11.12
+        },
+        "C": -5,
+        "D": false
+    }
+    */
+    //      Constantly recreating `db` takes time, so we make test dependent
+    //  on each other.
+    //      Generally speaking this is not great, but we cannot run them in
+    //  parallel anyway.
+    Context("Testing whether database operations report correct request ID.");
+    SubTest_RequestIDForCheck(db);
+    SubTest_RequestIDForIncrement(db);
+    SubTest_RequestIDForKeys(db);
+    SubTest_RequestIDForRead(db);
+    SubTest_RequestIDForRemove(db);
+    SubTest_RequestIDForSize(db);
+    SubTest_RequestIDForWrite(db);
+    __core().db.DeleteLocal(P("TEST_DB"));
+}
+
+protected static function SubTest_RequestIDForCheck(LocalDatabaseInstance db)
+{
+    local DBCheckTask task;
+
+    Issue("Type checking operation isn't returning correct request ID.");
+        task = db.CheckDataType(__().json.Pointer(P("/L")));
+    task.connect = DBCheckHandler;
+    task.TryCompleting();
+    TEST_ExpectTrue(default.resultRequestID == 0);
+    task = db.CheckDataType(__().json.Pointer(P("/L")), 29);
+    task.connect = DBCheckHandler;
+    task.TryCompleting();
+    TEST_ExpectTrue(default.resultRequestID == 29);
+}
+
+protected static function SubTest_RequestIDForIncrement(
+    LocalDatabaseInstance db)
+{
+    local DBIncrementTask task;
+
+    Issue("Increment operation isn't returning correct request ID.");
+    task = db.IncrementData(__().json.Pointer(P("/L")), __().box.int(29));
+    task.connect = DBIncrementHandler;
+    task.TryCompleting();
+    TEST_ExpectTrue(default.resultRequestID == 0);
+    task = db.IncrementData(__().json.Pointer(P("/L")), __().box.int(29), -7);
+    task.connect = DBIncrementHandler;
+    task.TryCompleting();
+    TEST_ExpectTrue(default.resultRequestID == -7);
+}
+
+protected static function SubTest_RequestIDForKeys(LocalDatabaseInstance db)
+{
+    local DBKeysTask task;
+
+    Issue("Keys list operation isn't returning correct request ID.");
+    task = db.GetDataKeys(__().json.Pointer(P("")));
+    task.connect = DBKeysHandler;
+    task.TryCompleting();
+    TEST_ExpectTrue(default.resultRequestID == 0);
+    task = db.GetDataKeys(__().json.Pointer(P("")), 11);
+    task.connect = DBKeysHandler;
+    task.TryCompleting();
+    TEST_ExpectTrue(default.resultRequestID == 11);
+}
+
+protected static function SubTest_RequestIDForRead(LocalDatabaseInstance db)
+{
+    local DBReadTask task;
+
+    Issue("Reading operation isn't returning correct request ID.");
+    task = db.ReadData(__().json.Pointer(P("/L")),);
+    task.connect = DBReadingHandler;
+    task.TryCompleting();
+    TEST_ExpectTrue(default.resultRequestID == 0);
+    task = db.ReadData(__().json.Pointer(P("/L")),, 666);
+    task.connect = DBReadingHandler;
+    task.TryCompleting();
+    TEST_ExpectTrue(default.resultRequestID == 666);
+}
+
+protected static function SubTest_RequestIDForRemove(LocalDatabaseInstance db)
+{
+    local DBRemoveTask task;
+
+    Issue("Removing operation isn't returning correct request ID.");
+    task = db.RemoveData(__().json.Pointer(P("/L")));
+    task.connect = DBRemoveHandler;
+    task.TryCompleting();
+    TEST_ExpectTrue(default.resultRequestID == 0);
+    task = db.RemoveData(__().json.Pointer(P("/L")), 80);
+    task.connect = DBRemoveHandler;
+    task.TryCompleting();
+    TEST_ExpectTrue(default.resultRequestID == 80);
+}
+
+protected static function SubTest_RequestIDForSize(LocalDatabaseInstance db)
+{
+    local DBSizeTask task;
+
+    Issue("Size getting operation isn't returning correct request ID.");
+    task = db.GetDataSize(__().json.Pointer(P("/L")));
+    task.connect = DBSizeHandler;
+    task.TryCompleting();
+    TEST_ExpectTrue(default.resultRequestID == 0);
+    task = db.GetDataSize(__().json.Pointer(P("/L")), 7);
+    task.connect = DBSizeHandler;
+    task.TryCompleting();
+    TEST_ExpectTrue(default.resultRequestID == 7);
+}
+
+protected static function SubTest_RequestIDForWrite(LocalDatabaseInstance db)
+{
+    local DBWriteTask task;
+
+    Issue("Writing operation isn't returning correct request ID.");
+    task = db.WriteData(__().json.Pointer(P("/L")), none);
+    task.connect = DBWritingHandler;
+    task.TryCompleting();
+    TEST_ExpectTrue(default.resultRequestID == 0);
+    task = db.WriteData(__().json.Pointer(P("/L")), none, 42);
+    task.connect = DBWritingHandler;
+    task.TryCompleting();
+    TEST_ExpectTrue(default.resultRequestID == 42);
+}
+
 defaultproperties
 {
     caseGroup   = "Database"

sources/Manifest.uc

@@ -54,7 +54,8 @@ defaultproperties
     testCases(25)   = class'TEST_BigInt'
     testCases(26)   = class'TEST_DatabaseCommon'
     testCases(27)   = class'TEST_LocalDatabase'
-    testCases(28)   = class'TEST_AcediaConfig'
+    testCases(28)   = class'TEST_DBConnection'
-    testCases(29)   = class'TEST_UTF8EncoderDecoder'
+    testCases(29)   = class'TEST_AcediaConfig'
-    testCases(30)   = class'TEST_AvariceStreamReader'
+    testCases(30)   = class'TEST_UTF8EncoderDecoder'
+    testCases(31)   = class'TEST_AvariceStreamReader'
 }

sources/Players/EPlayer.uc

@@ -57,6 +57,7 @@ protected function Finalizer()
 {
     _.memory.Free(controller);
     _.memory.Free(consoleInstance);
+    _.memory.Free(identity);
     controller      = none;
     consoleInstance = none;
     //  No need to deallocate `User` objects, since they are all have unique
@@ -96,7 +97,6 @@ public final /* unreal */ function bool Initialize(
         idHash = _.text.FromString(initController.GetPlayerIDHash());
         identity = _.users.FetchByIDHash(idHash);
         idHash.FreeSelf();
-        idHash = none;
     }
     signalsReferences   = playerSignals;
     controller          = _server.unreal.ActorRef(initController);
@@ -121,6 +121,9 @@ public function EInterface Copy()
         //  not initialized
         return playerCopy;
     }
+    if (identity != none) {
+        identity.NewRef();
+    }
     playerCopy.identity = identity;
     playerCopy.Initialize(  PlayerController(controller.Get()),
                             signalsReferences);

sources/Text/BaseText.uc

@@ -404,6 +404,54 @@ public final function MutableText UpperMutableCopy(
     return textCopy;
 }
 
+/**
+ *  Checks whether all letters in the caller text is in the lower case.
+ *
+ *  @return `true` if there are no characters that qualify as upper case and
+ *      `false` otherwise.
+ */
+public final function bool IsLowerCase()
+{
+    local int       i;
+    local Character nextCharacter;
+
+    if (IsEmpty()) {
+        return true;
+    }
+    for (i = 0; i < GetLength(); i += 1)
+    {
+        nextCharacter = GetCharacter(i);
+        if (_.text.IsUpper(nextCharacter)) {
+            return false;
+        }
+    }
+    return true;
+}
+
+/**
+ *  Checks whether all letters in the caller text is in the lower case.
+ *
+ *  @return `true` if there are no characters that qualify as lower case and
+ *      `false` otherwise.
+ */
+public final function bool IsUpperCase()
+{
+    local int       i;
+    local Character nextCharacter;
+
+    if (IsEmpty()) {
+        return true;
+    }
+    for (i = 0; i < GetLength(); i += 1)
+    {
+        nextCharacter = GetCharacter(i);
+        if (_.text.IsLower(nextCharacter)) {
+            return false;
+        }
+    }
+    return true;
+}
+
 /**
  *  Checks if caller `BaseText` contains a valid name object or not.
  *

sources/Text/JSON/JSONAPI.uc

@@ -5,7 +5,7 @@
  *  both valid and invalid JSON. However only correctly parsing valid JSON 
  *  is guaranteed. This means that you should not rely on these methods to parse
  *  any JSON extensions or validate JSON for you.
- *      Copyright 2021-2022 Anton Tarasenko
+ *      Copyright 2021-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -1381,6 +1381,315 @@ private final function int GetEscapedVersion(int codePoint)
     return codePoint;
 }
 
+/**
+ *  Increments given value by another value, producing result as a new
+ *  JSON-compatible value.
+ *
+ *      What "incrementing" actually does depends on the passed JSON values:
+ *  `valueToIncrement` and `increment` parameters. Unless either of them is `none`
+ *  (then "increment" simply acts as a `_.json.Copy()` method for
+ *  the non-`none` one), they must represent the same JSON type and:
+ *
+ *      1.  JSON bool: performs logical "or" operation on given values;
+ *      2.  JSON number: adds values together;
+ *      3.  JSON string: appends `increment` at the end of `valueToIncrement`;
+ *      4.  JSON array: appends copy of elements of `increment` at the end of
+ *          array of copies of elements of `valueToIncrement`
+ *          (calls `ArrayList::append()` method);
+ *      5.  JSON object: creates new collection, based on `valueToIncrement`
+ *          with added key-value pairs from `increment` (all elements are
+ *          copied). Does not override old values
+ *          (calls `HashTable::append()` method).
+ *
+ *  In case they represent different JSON types (that aren't "null") -
+ *  incrementing should produce `none`.
+ *
+ *  @param  valueToIncrement    Value to increment. Can be any JSON-compatible
+ *      value.
+ *  @param  increment           Value to increment it by. Can be any
+ *      JSON-compatible value.
+ *  @return Incremented data (guaranteed to contain copies and not actual
+ *      objects from either `valueToIncrement` or `increment`). `none` if
+ *      argument types were incompatible. Whether type of the result will be
+ *      immutable (boxes and `Text`) or mutable (refs and `MutableText`)
+ *      depends on immutability of `valueToIncrement`. When adding two numbers,
+ *      whether result will be boxed (this includes both boxes and refs) `int`
+ *      or `float` depends on both parameters - if either of them if `float`,
+ *      then result will be `float`.
+ */
+public final function AcediaObject Increment(
+    AcediaObject valueToIncrement,
+    AcediaObject increment)
+{
+    local AcediaObject result;
+
+    if (valueToIncrement == none) {
+        result = _.json.Copy(increment);
+    }
+    else if (increment == none) {
+        result = _.json.Copy(valueToIncrement);
+    }
+    else if (   valueToIncrement.class == class'IntBox'
+        ||      valueToIncrement.class == class'IntRef'
+        ||      valueToIncrement.class == class'FloatBox'
+        ||      valueToIncrement.class == class'FloatRef')
+    {
+        result = Increment_Number(valueToIncrement, increment);
+    }
+    else if (   valueToIncrement.class == class'BoolBox'
+        ||      valueToIncrement.class == class'BoolRef')
+    {
+        result = Increment_Bool(valueToIncrement, increment);
+    }
+    else if (   valueToIncrement.class == class'Text'
+        ||      valueToIncrement.class == class'MutableText')
+    {
+        result = Increment_Text(valueToIncrement, increment);
+    }
+    else {
+        result = Increment_Collections(valueToIncrement, increment);
+    }
+    return result;
+}
+
+//  Assumes `valueToIncrement` and `increment` aren't `none`
+private final function AcediaObject Increment_Collections(
+    AcediaObject valueToIncrement,
+    AcediaObject increment)
+{
+    local AcediaObject  result;
+    local ArrayList     arrayListCopy;
+    local HashTable     hashTableCopy;
+
+    if (    valueToIncrement.class == class'ArrayList'
+        &&  increment.class == class'ArrayList')
+    {
+        arrayListCopy = ArrayList(Copy(ArrayList(increment)));
+        result = CopyArrayList(ArrayList(valueToIncrement))
+            .Append(arrayListCopy);
+        _.memory.Free(arrayListCopy);
+    }
+    else if (   valueToIncrement.class == class'HashTable'
+            &&  increment.class == class'HashTable')
+    {
+        hashTableCopy = HashTable(Copy(HashTable(increment)));
+        result = CopyHashTable(HashTable(valueToIncrement))
+            .Append(hashTableCopy);
+        _.memory.Free(hashTableCopy);
+    }
+    return result;
+}
+
+//  Assumes `valueToIncrement` and `increment` aren't `none`
+private final function AcediaObject Increment_Text(
+    AcediaObject valueToIncrement,
+    AcediaObject increment)
+{
+    local BaseText      textIncrement;
+    local MutableText   builder;
+
+    textIncrement = BaseText(increment);
+    if (BaseText(increment) == none) {
+        return none;
+    }
+    builder = BaseText(valueToIncrement).MutableCopy();
+    builder.Append(textIncrement);
+    if (Text(valueToIncrement) != none) {
+        return builder.IntoText();
+    }
+    return builder;
+}
+
+//  Assumes `valueToIncrement` and `increment` aren't `none`
+private final function AcediaObject Increment_Bool(
+    AcediaObject valueToIncrement,
+    AcediaObject increment)
+{
+    local bool value1, value2;
+
+    if (valueToIncrement.class == class'BoolBox') {
+        value1 = BoolBox(valueToIncrement).Get();
+    }
+    if (valueToIncrement.class == class'BoolRef') {
+        value1 = BoolRef(valueToIncrement).Get();
+    }
+    if (increment.class == class'BoolBox') {
+        value2 = BoolBox(increment).Get();
+    }
+    else if (increment.class == class'BoolRef') {
+        value2 = BoolRef(increment).Get();
+    }
+    else {
+        return none;
+    }
+    if (ValueBox(valueToIncrement) != none) {
+        return _.box.bool(value1 || value2);
+    }
+    return _.ref.bool(value1 || value2);
+}
+
+//      Assumes `valueToIncrement` and `increment` aren't `none`
+//      Assumes `valueToIncrement` is one of four classes: `IntBox`, `IntRef`,
+//  `FloatBox` or `FloatRef`.
+private final function AcediaObject Increment_Number(
+    AcediaObject valueToIncrement,
+    AcediaObject increment)
+{
+    local bool  hasFloats;
+    local int   intSummand1, intSummand2, intSum;
+    local float floatSummand1, floatSummand2, floatSum;
+
+    hasFloats = valueToIncrement.class == class'FloatBox'
+        ||  valueToIncrement.class == class'FloatRef'
+        ||  increment.class == class'FloatBox'
+        ||  increment.class == class'FloatRef';
+    //  `valueToIncrement` is guaranteed to have an appropriate type,
+    //  but `increment` might not, so only do check on second call
+    ExtractBoxedNumericValue(valueToIncrement, intSummand1, floatSummand1);
+    if (!ExtractBoxedNumericValue(increment, intSummand2, floatSummand2)) {
+        return none;
+    }
+    if (hasFloats)
+    {
+        floatSum = floatSummand1 + floatSummand2
+            + float(intSummand1 + intSummand2);
+        if (ValueBox(valueToIncrement) != none) {
+            return _.box.float(floatSum);
+        }
+        return _.ref.float(floatSum);
+    }
+    intSum = intSummand1 + intSummand2 + int(floatSummand1 + floatSummand2);
+    if (ValueBox(valueToIncrement) != none) {
+        return _.box.int(intSum);
+    }
+    return _.ref.int(intSum);
+}
+
+//  Extracts numeric value and records it into one of two out arguments:
+//
+//      *   `asInteger` iff `value` is either `IntBox` or `IntRef`;
+//      *   `asFloat` iff `value` is either `FloatBox` or `FloatRef`;
+//
+//  Does not change the value in remaining parameter.
+//  Returns `true` in case of success (method managed to read the value) and
+//  `false` otherwise (`value` had non-numeric or unknown type).
+private final function bool ExtractBoxedNumericValue(
+    AcediaObject    value,
+    out int         asInteger,
+    out float       asFloat)
+{
+    local bool success;
+
+    if (value.class == class'IntBox')
+    {
+        asInteger = IntBox(value).Get();
+        success = true;
+    }
+    else if (value.class == class'IntRef')
+    {
+        asInteger = IntRef(value).Get();
+        success = true;
+    }
+    else if (value.class == class'FloatBox')
+    {
+        asFloat = FloatBox(value).Get();
+        success = true;
+    }
+    else if (value.class == class'FloatRef')
+    {
+        asFloat = FloatRef(value).Get();
+        success = true;
+    }
+    return success;
+}
+
+/**
+ *  Performs a deep copy of the `inputData`. This means it copies not only
+ *  `inputData` itself, but (in case it is a container) all of the values
+ *  within it, instead of simply storing the same references (as opposed to
+ *  shallow copy). Stored values also recursively deep copied.
+ *
+ *  @param  inputData   Data to copy. Can be any JSON-compatible value.
+ *  @return Copy of the `inputData`. Any non-JSON values are copied as `none`.
+ */
+public final function AcediaObject Copy(AcediaObject inputData)
+{
+    if (inputData == none) {
+        return none;
+    }
+    if (inputData.class == class'IntBox') {
+        return _.box.int(IntBox(inputData).Get());
+    }
+    if (inputData.class == class'IntRef') {
+        return _.ref.int(IntRef(inputData).Get());
+    }
+    if (inputData.class == class'BoolBox') {
+        return _.box.bool(BoolBox(inputData).Get());
+    }
+    if (inputData.class == class'BoolRef') {
+        return _.ref.bool(BoolRef(inputData).Get());
+    }
+    if (inputData.class == class'FloatBox') {
+        return _.box.float(FloatBox(inputData).Get());
+    }
+    if (inputData.class == class'FloatRef') {
+        return _.ref.float(FloatRef(inputData).Get());
+    }
+    if (inputData.class == class'Text') {
+        return Text(inputData).Copy();
+    }
+    if (inputData.class == class'MutableText') {
+        return MutableText(inputData).MutableCopy();
+    }
+    if (inputData.class == class'ArrayList') {
+        return CopyArrayList(ArrayList(inputData));
+    }
+    if (inputData.class == class'HashTable') {
+        return CopyHashTable(HashTable(inputData));
+    }
+    return none;
+}
+
+private final function ArrayList CopyArrayList(ArrayList inputList)
+{
+    local int           i, inputListLength;
+    local ArrayList     result;
+    local AcediaObject  nextObject, nextCopy;
+
+    result = _.collections.EmptyArrayList();
+    inputListLength = inputList.GetLength();
+    for (i = 0; i < inputListLength; i += 1)
+    {
+        nextObject = inputList.GetItem(i);
+        nextCopy = Copy(nextObject);
+        result.AddItem(nextCopy);
+        _.memory.Free(nextCopy);
+        _.memory.Free(nextObject);
+    }
+    return result;
+}
+
+private final function HashTable CopyHashTable(HashTable inputTable)
+{
+    local int           i;
+    local HashTable     result;
+    local array<Text>   textKeys;
+    local AcediaObject  nextObject, nextCopy;
+
+    result = _.collections.EmptyHashTable();
+    textKeys = inputTable.GetTextKeys();
+    for (i = 0; i < textKeys.length; i += 1)
+    {
+        nextObject = inputTable.GetItem(textKeys[i]);
+        nextCopy = Copy(nextObject);
+        result.SetItem(textKeys[i], nextCopy);
+        _.memory.Free(nextCopy);
+        _.memory.Free(nextObject);
+    }
+    _.memory.FreeMany(textKeys);
+    return result;
+}
+
 defaultproperties
 {
     MAX_FLOAT_PRECISION = 4

sources/Text/JSON/JSONPointer.uc

@@ -5,7 +5,7 @@
  *  Path "/a/b/c" will be stored as a sequence of components "a", "b" and "c",
  *  path "/" will be stored as a singular empty component ""
  *  and empty path "" would mean that there is not components at all.
- *      Copyright 2021 Anton Tarasenko
+ *      Copyright 2021-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -293,6 +293,30 @@ public final function int GetNumericComponent(int index)
     return components[index].asNumber;
 }
 
+/**
+ *  Checks whether component at given index can be used to index array.
+ *
+ *  This method accepts numeric components plus component equal to "-", that can
+ *  be used to point at the element after the last on in the `JSONArray`.
+ *
+ *  @param  index   Index of the component to check.
+ *  @param  `true` if component with given index exists and it either positive
+ *      number or "-".
+ */
+public final function bool IsComponentArrayApplicable(int index)
+{
+    local bool isAddElementAlias;
+    local Text component;
+
+    if (GetNumericComponent(index) >= 0) {
+        return true;
+    }
+    component = GetComponent(index);
+    isAddElementAlias = P("-").IsEqual(component);
+    _.memory.Free(component);
+    return isAddElementAlias;
+}
+
 /**
  *  Converts caller `JSONPointer` into it's `Text` representation.
  *
@@ -375,18 +399,42 @@ public final function int GetFoldsAmount()
 /**
  *  Makes an exact copy of the caller `JSONPointer`.
  *
- *  @return Copy of the caller `JSONPointer`.
+ *  Copies components in the range `[startIndex; startIndex + maxLength - 1]`
+ *  If provided parameters `startIndex` and `maxLength` define a range that
+ *  goes beyond `[0; self.GetLength() - 1]`, then intersection with a valid
+ *  range will be used.
+ *
+ *  @param  startIndex  Position of the first component to copy.
+ *      By default `0`, corresponding to the very first component.
+ *  @param  maxLength   Max length of the extracted JSON pointer (in amount of
+ *      components). By default `0` - that and all negative values mean that
+ *      method should extract all components to the right of `startIndex`.
+ *  @return Copy of the specified range of the caller `JSONPointer`.
  */
-public final function JSONPointer Copy()
+public final function JSONPointer Copy(
+    optional int startIndex,
+    optional int maxLength)
 {
-    local int               i;
+    local int               i, endIndex;
     local JSONPointer       newPointer;
     local array<Component>  newComponents;
-    newComponents = components;
+
-    for (i = 0; i < newComponents.length; i += 1)
+    if (maxLength <= 0) {
+        maxLength = components.length - startIndex;
+    }
+    endIndex = startIndex + maxLength;
+    if (endIndex <= 0) {
+        return JSONPointer(_.memory.Allocate(class'JSONPointer'));
+    }
+    startIndex  = Max(startIndex, 0);
+    endIndex    = Min(endIndex, components.length);
+    for (i = startIndex; i < endIndex; i += 1)
     {
-        if (newComponents[i].asText != none) {
+        newComponents[newComponents.length] = components[i];
-            newComponents[i].asText = newComponents[i].asText.MutableCopy();
+        if (components[i].asText != none)
+        {
+            newComponents[newComponents.length - 1].asText =
+                components[i].asText.MutableCopy();
         }
     }
     newPointer = JSONPointer(_.memory.Allocate(class'JSONPointer'));
@@ -394,6 +442,85 @@ public final function JSONPointer Copy()
     return newPointer;
 }
 
+/**
+ *  Appends path, contained in JSON pointer `other` to the caller JSON pointer.
+ *  Appending "/A/B/7/C" to "/object/hey/1/there/" produces
+ *  "/object/hey/1/there//A/B/7/C".
+ *
+ *  @param  other   Pointer to append. If `none` - caller `JSONPointer` will
+ *      not change.
+ *  @return Reference to the caller `JSONPointer` to allow for method chaining.
+ */
+public final function JSONPointer Append(JSONPointer other)
+{
+    local int               i;
+    local array<Component>  otherComponents;
+
+    if (other == none) {
+        return self;
+    }
+    otherComponents = other.components;
+    for (i = 0; i < otherComponents.length; i += 1)
+    {
+        if (otherComponents[i].asText != none) {
+            otherComponents[i].asText = otherComponents[i].asText.MutableCopy();
+        }
+        components[components.length] = otherComponents[i];
+    }
+    return self;
+}
+
+/**
+ *  Checks if given pointer corresponds with the beginning of the caller one.
+ *
+ *  Pointer starts with another one if it includes all of its fields from
+ *  the beginning and in order
+ *  E.g. "/A/B/C" starts with "/A/B", but not with "/A/B/C/D", "/D/A/B/C" or
+ *  "/A/B/CD".
+ *
+ *  @param  other   Candidate into being caller pointer's prefix.
+ *  @return `true` if `other` is prefix and `false` otherwise. `none` is
+ *      considered to be an empty pointer and, therefore, prefix to any other
+ *      pointer.
+ */
+public final function bool StartsWith(JSONPointer other)
+{
+    local int               i;
+    local array<Component>  otherComponents;
+
+    //  `none` is same as empty
+    if (other == none)                              return true;
+    otherComponents = other.components;
+    //  Not enough length
+    if (components.length < otherComponents.length) return false;
+
+    for (i = 0; i < otherComponents.length; i += 1)
+    {
+        //  Compare numeric components if at least one is such
+        if (    components[i].testedForBeingNumeric
+            ||  otherComponents[i].testedForBeingNumeric)
+        {
+            if (GetNumericComponent(i) != other.GetNumericComponent(i)) {
+                return false;
+            }
+            //      End this iteration for numeric component, but continue for
+            //  text ones
+            if (GetNumericComponent(i) >= 0) {
+                continue;
+            }
+        }
+        //  We can reach here if:
+        //      1.  Neither components have `testedForBeingNumeric` set to
+        //          `true`, neither `asText` fields are `none` by the invariant;
+        //      2.  At least one had `testedForBeingNumeric`, but they tested
+        //  negative for being numeric.
+        if (!components[i].asText.Compare(otherComponents[i].asText)) {
+            return false;
+        }
+    }
+    return true;
+}
+
 defaultproperties
 {
     TSLASH                  = 0

sources/Text/Tests/TEST_JSON.uc

@@ -1,6 +1,6 @@
 /**
  *  Set of tests for functionality of JSON printing/parsing.
- *      Copyright 2021-2022 Anton Tarasenko
+ *      Copyright 2021-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -22,11 +22,18 @@ class TEST_JSON extends TestCase
 
 var string simpleJSONObject, complexJSONObject;
 
+protected static function JSONPointer MakePtr(string str)
+{
+    return __().json.Pointer(__().text.FromString(str));
+}
+
 protected static function TESTS()
 {
     Test_Pointer();
     Test_Print();
     Test_Parse();
+    Test_Copy();
+    Test_Incrementing();
 }
 
 protected static function Test_Pointer()
@@ -37,6 +44,10 @@ protected static function Test_Pointer()
     SubTest_PointerPushPop();
     SubTest_PointerNumeric();
     SubTest_PopWithoutRemoving();
+    SubTest_Append();
+    SubText_Copy();
+    SubTest_StartsWith();
+    SubTest_IsComponentArrayApplicable();
 }
 
 protected static function SubTest_PointerCreate()
@@ -187,6 +198,114 @@ protected static function SubTest_PopWithoutRemoving()
     TEST_ExpectTrue(pointer.Pop(true).ToString() == "simple");
 }
 
+protected static function SubTest_Append()
+{
+    local JSONPointer pointer, append;
+    Issue("Appending another JSON pointer is not working correctly.");
+    pointer = __().json.Pointer(P("/object/hey/1/there/"));
+    append = __().json.Pointer(P("/A/B/7/C"));
+    pointer.Append(append);
+    TEST_ExpectTrue(
+            pointer.ToText().ToString()
+        ==  "/object/hey/1/there//A/B/7/C");
+    pointer = __().json.Pointer(P(""));
+    append = __().json.Pointer(P("/A/B/7/C"));
+    pointer.Append(append);
+    TEST_ExpectTrue(pointer.ToText().ToString() == "/A/B/7/C");
+    pointer = __().json.Pointer(P("/object/hey/1/there/"));
+    append = __().json.Pointer(P(""));
+    pointer.Append(append);
+    TEST_ExpectTrue(pointer.ToText().ToString() == "/object/hey/1/there/");
+    pointer = __().json.Pointer(P("/object/hey/1/there/"));
+    pointer.Append(none);
+    TEST_ExpectTrue(pointer.ToText().ToString() == "/object/hey/1/there/");
+}
+
+protected static function SubText_Copy()
+{
+    Issue("JSON pointer's `Copy()` method does not correctly copy the whole"
+        @ "pointer.");
+    TEST_ExpectTrue(MakePtr("/A/B/3/D").Copy().ToText().ToString()
+        == "/A/B/3/D");
+    TEST_ExpectTrue(MakePtr("/").Copy().ToText().ToString() == "/");
+    TEST_ExpectTrue(MakePtr("").Copy().ToText().ToString() == "");
+    TEST_ExpectTrue(MakePtr("/A/B/3/D").Copy(0, 4).ToText().ToString()
+        == "/A/B/3/D");
+    TEST_ExpectTrue(MakePtr("/A/B/3/D").Copy(-2).ToText().ToString()
+        == "/A/B/3/D");
+    TEST_ExpectTrue(MakePtr("/A/B/3/D").Copy(0, 7).ToText().ToString()
+        == "/A/B/3/D");
+    TEST_ExpectTrue(MakePtr("/A/B/3/D").Copy(-3, 7).ToText().ToString()
+        == "/A/B/3/D");
+    TEST_ExpectTrue(MakePtr("/A/B/3/D").Copy(-5, 20).ToText().ToString()
+        == "/A/B/3/D");
+    TEST_ExpectTrue(MakePtr("").Copy(-1).ToText().ToString() == "");
+
+    Issue("JSON pointer's `Copy()` method does not correctly copy empty range"
+        @ "of the pointer.");
+    TEST_ExpectTrue(MakePtr("/A/B/3/D").Copy(-5, 4).ToText().ToString() == "");
+    TEST_ExpectTrue(MakePtr("/A/B/3/D").Copy(4, 11).ToText().ToString() == "");
+
+    Issue("JSON pointer's `Copy()` method does not correctly copy partial"
+        @ "intersection range of the pointer.");
+    TEST_ExpectTrue(MakePtr("/A//3/D").Copy(-5, 8).ToText().ToString()
+        == "/A//3");    //  left
+    TEST_ExpectTrue(MakePtr("/A//3/D").Copy(1, 11).ToText().ToString()
+        == "//3/D");    //  right
+}
+
+protected static function SubTest_StartsWith()
+{
+    local JSONPointer pointer;
+
+    Issue("Any pointers start with `none` JSON pointer.");
+    TEST_ExpectTrue(__().json.Pointer(P("/A/B/C")).StartsWith(none));
+    TEST_ExpectTrue(__().json.Pointer(P("/")).StartsWith(none));
+    TEST_ExpectTrue(__().json.Pointer(P("")).StartsWith(none));
+
+    Issue("`StartsWith()` correctly detects JSON pointers that are actually"
+        @ "their prefixes.");
+    TEST_ExpectTrue(__().json.Pointer(P("/A/7/C"))
+        .StartsWith(__().json.Pointer(P("/A/7/C"))));
+    //  Same, but constructed manually to handle components added as numeric
+    pointer = __().json.Pointer().Push(P("A")).PushNumeric(7).Push(P("C"));
+    TEST_ExpectTrue(pointer.StartsWith(__().json.Pointer(P("/A/7/C"))));
+    TEST_ExpectTrue(__().json.Pointer(P("/A/7/C"))
+        .StartsWith(__().json.Pointer(P("/A/7"))));
+    TEST_ExpectTrue(__().json.Pointer(P("/A/7/C"))
+        .StartsWith(__().json.Pointer(P(""))));
+    TEST_ExpectTrue(__().json.Pointer(P(""))
+        .StartsWith(__().json.Pointer(P(""))));
+
+    Issue("`StartsWith()` correctly detects JSON pointers that aren't actually"
+        @ "their prefixes.");
+    TEST_ExpectFalse(__().json.Pointer(P("/A/7/C"))
+        .StartsWith(__().json.Pointer(P("/A/3/C"))));
+    //  Constructed manually to handle components added as numeric
+    pointer = __().json.Pointer().Push(P("A")).PushNumeric(8).Push(P("C"));
+    TEST_ExpectFalse(pointer.StartsWith(__().json.Pointer(P("/A/3/C"))));
+    TEST_ExpectFalse(__().json.Pointer(P("/A/7/C"))
+        .StartsWith(__().json.Pointer(P("/A/7/"))));
+    TEST_ExpectFalse(__().json.Pointer(P("/A/7/C"))
+        .StartsWith(__().json.Pointer(P("/"))));
+}
+
+protected static function SubTest_IsComponentArrayApplicable()
+{
+    Issue("`IsComponentArrayApplicable()` method wrongly detects numeric"
+        @ "components.");
+    TEST_ExpectFalse(
+        __().json.Pointer(P("/A/B/C")).IsComponentArrayApplicable(0));
+    TEST_ExpectTrue(
+        __().json.Pointer(P("/A/2/C")).IsComponentArrayApplicable(1));
+    TEST_ExpectTrue(
+        __().json.Pointer(P("/A/B/-")).IsComponentArrayApplicable(2));
+    TEST_ExpectFalse(
+        __().json.Pointer(P("/A/7/C")).IsComponentArrayApplicable(-2));
+    TEST_ExpectFalse(
+        __().json.Pointer(P("/A/7/C")).IsComponentArrayApplicable(10));
+}
+
 protected static function Test_Print()
 {
     Context("Testing printing simple JSON values.");
@@ -651,6 +770,399 @@ protected static function SubTest_ParseComplex()
     TEST_ExpectTrue(FloatBox(inner.GetItem(P("maybe"))).Get() == 0.003);
 }
 
+protected static function Test_Copy()
+{
+    Context("Testing method for copying JSON values.");
+    SubTest_CopySimple();
+    SubTest_CopyComplex();
+}
+
+protected static function SubTest_CopySimple()
+{
+    Issue("JSON's `Copy()` method incorrectly copies copy boxed built-in"
+        @ "types.");
+    TEST_ExpectNone(__().json.Copy(none));
+    TEST_ExpectTrue(
+            BoolBox(__().json.Copy(__().box.bool(true))).Get()
+        ==  true);
+    TEST_ExpectTrue(
+            BoolRef(__().json.Copy(__().ref.bool(false))).Get()
+        ==  false);
+    TEST_ExpectTrue(IntBox(__().json.Copy(__().box.int(-7))).Get() == -7);
+    TEST_ExpectTrue(
+            IntRef(__().json.Copy(__().ref.int(234234))).Get()
+        ==  234234);
+    TEST_ExpectTrue(
+            FloatBox(__().json.Copy(__().box.float(3.76))).Get() 
+        ==  3.76);
+    TEST_ExpectTrue(
+            FloatRef(__().json.Copy(__().ref.float(-213.1))).Get()
+        ==  -213.1);
+    TEST_ExpectTrue(Text(__().json.Copy(P("Hey!"))).ToString() == "Hey!");
+    TEST_ExpectTrue(
+            MutableText(__().json.Copy(__().text.FromStringM("Hey!")))
+                .ToString()
+        ==  "Hey!");
+}
+
+protected static function HashTable ConstructComplexJSONObject()
+{
+    local HashTable result, innerObject, deepObject, oneMoreObject;
+    local ArrayList innerArray;
+
+    deepObject = __().collections.EmptyHashTable();
+    deepObject.SetItem(P("something \"here\""), P("yes"));
+    deepObject.SetFloat(P("maybe"), 0.003);
+    innerArray = __().collections.EmptyArrayList();
+    innerArray.AddString("Engine.Actor");
+    innerArray.AddBool(false);
+    innerArray.AddItem(none);
+    innerArray.AddItem(deepObject);
+    innerArray.AddFloat(56.6);
+    oneMoreObject = __().collections.EmptyHashTable();
+    oneMoreObject.SetInt(P("nope"), 324532);
+    oneMoreObject.SetBool(P("whatever"), false);
+    oneMoreObject.SetString(P("o rly?"), "ya rly");
+    innerObject = __().collections.EmptyHashTable();
+    innerObject.SetBool(P("my_bool"), true);
+    innerObject.SetItem(P("array"), innerArray);
+    innerObject.SetItem(P("one more"), oneMoreObject);
+    innerObject.SetInt(P("my_int"), -9823452);
+    result = __().collections.EmptyHashTable();
+    result.SetItem(P("innerObject"), innerObject);
+    result.SetFloat(P("some_var"), -7.32);
+    result.SetString(P("another_var"), "aye!");
+    return result;
+}
+
+protected static function SubTest_CopyComplex()
+{
+    local HashTable complexCopy;
+
+    complexCopy = HashTable(__().json.Copy(ConstructComplexJSONObject()));
+    TEST_ExpectTrue(complexCopy.GetBoolBy(P("/innerObject/my_bool")) == true);
+    TEST_ExpectTrue(
+        complexCopy.GetStringBy(P("/innerObject/array/0")) == "Engine.Actor");
+    TEST_ExpectTrue(
+        complexCopy.GetBoolBy(P("/innerObject/array/1")) == false);
+    TEST_ExpectTrue(
+        complexCopy.GetItemBy(P("/innerObject/array/2")) == none);
+    TEST_ExpectTrue(
+            complexCopy.GetStringBy(P("/innerObject/array/3/something \"here\""))
+        ==  "yes");
+    TEST_ExpectTrue(
+        complexCopy.GetFloatBy(P("/innerObject/array/3/maybe")) == 0.003);
+    TEST_ExpectTrue(
+        complexCopy.GetFloatBy(P("/innerObject/array/4")) == 56.6);
+    TEST_ExpectTrue(
+        complexCopy.GetIntBy(P("/innerObject/one more/nope")) == 324532);
+    TEST_ExpectTrue(
+        complexCopy.GetBoolBy(P("/innerObject/one more/whatever")) == false);
+    TEST_ExpectTrue(
+        complexCopy.GetStringBy(P("/innerObject/one more/o rly?")) == "ya rly");
+    TEST_ExpectTrue(
+        complexCopy.GetIntBy(P("/innerObject/my_int")) == -9823452);
+    TEST_ExpectTrue(
+        complexCopy.GetFloatBy(P("/some_var")) == -7.32);
+    TEST_ExpectTrue(
+        complexCopy.GetStringBy(P("/another_var")) == "aye!");
+}
+
+protected static function Test_Incrementing()
+{
+    Context("Testing incrementing JSON values with `_.json.Increment()`.");
+    SubTest_Incrementing_Null();
+    SubTest_Incrementing_Bool();
+    SubTest_Incrementing_Number();
+    SubTest_Incrementing_String();
+    SubTest_Incrementing_Array();
+    SubTest_Incrementing_Object();
+    SubTest_Incrementing_Incompatible();
+}
+
+protected static function SubTest_Incrementing_Null()
+{
+    local FloatRef ref;
+
+    Issue("Null values aren't incremented correctly.");
+    TEST_ExpectNone(__().json.Increment(none, none));
+    TEST_ExpectTrue(BoolBox(__().json.Increment(
+        none, __().box.bool(true))).Get() == true);
+    TEST_ExpectTrue(FloatRef(__().json.Increment(
+        __().ref.float(11.5), none)).Get() == 11.5);
+
+    Issue("Incrementing null values simply copies reference.");
+    ref = __().ref.float(1032423.91);
+    TEST_ExpectFalse(__().json.Increment(ref, none) == none);
+    TEST_ExpectFalse(__().json.Increment(none, ref) == none);
+}
+
+protected static function SubTest_Incrementing_Bool()
+{
+    Issue("Boolean values aren't incremented correctly.");
+    TEST_ExpectTrue(BoolBox(__().json.Increment(
+        __().box.bool(false), __().box.bool(false))).Get() == false);
+    TEST_ExpectTrue(BoolBox(__().json.Increment(
+        __().box.bool(true), __().box.bool(false))).Get() == true);
+    TEST_ExpectTrue(BoolBox(__().json.Increment(
+        __().box.bool(false), __().box.bool(true))).Get() == true);
+    TEST_ExpectTrue(BoolBox(__().json.Increment(
+        __().box.bool(true), __().box.bool(true))).Get() == true);
+    
+    Issue("Incrementing boolean values produces incorrect type.");
+    TEST_ExpectTrue(BoolBox(__().json.Increment(
+        __().box.bool(false), __().box.bool(true))).Get() == true);
+    TEST_ExpectTrue(BoolBox(__().json.Increment(
+        __().box.bool(false), __().ref.bool(true))).Get() == true);
+    TEST_ExpectTrue(BoolRef(__().json.Increment(
+        __().ref.bool(false), __().box.bool(true))).Get() == true);
+    TEST_ExpectTrue(BoolRef(__().json.Increment(
+        __().ref.bool(false), __().ref.bool(true))).Get() == true);
+}
+
+protected static function SubTest_Incrementing_Number()
+{
+    SubSubTest_Incrementing_Number_Pure();
+    SubSubTest_Incrementing_Number_Mixed();
+}
+
+protected static function SubSubTest_Incrementing_Number_Pure()
+{
+    Issue("Numeric values aren't incremented correctly (for boxed `int`s).");
+    TEST_ExpectTrue(IntBox(__().json.Increment(
+        __().box.int(3), __().box.int(-3))).Get() == 0);
+    TEST_ExpectTrue(IntBox(__().json.Increment(
+        __().box.int(-4), __().ref.int(11))).Get() == 7);
+    TEST_ExpectTrue(IntRef(__().json.Increment(
+        __().ref.int(124), __().box.int(624))).Get() == 748);
+    TEST_ExpectTrue(IntRef(__().json.Increment(
+        __().ref.int(345), __().ref.int(-23423))).Get() == -23078);
+
+    Issue("Numeric values aren't incremented correctly (for boxed `float`s).");
+    TEST_ExpectTrue(FloatBox(__().json.Increment(
+        __().box.float(11.2), __().box.float(-0.2))).Get() == 11);
+    TEST_ExpectTrue(FloatBox(__().json.Increment(
+        __().box.float(1012.78), __().ref.float(0.12))).Get() == 1012.9);
+    TEST_ExpectTrue(FloatRef(__().json.Increment(
+        __().ref.float(12), __().box.float(13))).Get() == 25);
+    TEST_ExpectTrue(FloatRef(__().json.Increment(
+        __().ref.float(-0.32), __().ref.float(0.32))).Get() == 0);
+}
+
+protected static function SubSubTest_Incrementing_Number_Mixed()
+{
+    Issue("Numeric values aren't incremented correctly (for mixed `int`s and"
+        @ "`float`s).");
+    TEST_ExpectTrue(FloatBox(__().json.Increment(
+        __().box.float(11.2), __().box.int(0))).Get() == 11.2);
+    TEST_ExpectTrue(FloatBox(__().json.Increment(
+        __().box.float(1012.78), __().ref.int(2))).Get() == 1014.78);
+    TEST_ExpectTrue(FloatRef(__().json.Increment(
+        __().ref.float(12), __().box.int(13))).Get() == 25);
+    TEST_ExpectTrue(FloatRef(__().json.Increment(
+        __().ref.float(-0.32), __().ref.int(14))).Get() == 13.68);
+
+    TEST_ExpectTrue(FloatBox(__().json.Increment(
+        __().box.int(11), __().box.float(-0.2))).Get() == 10.8);
+    TEST_ExpectTrue(FloatBox(__().json.Increment(
+        __().box.int(1012), __().ref.float(7.12))).Get() == 1019.12);
+    TEST_ExpectTrue(FloatRef(__().json.Increment(
+        __().ref.int(12), __().box.float(13.1))).Get() == 25.1);
+    TEST_ExpectTrue(FloatRef(__().json.Increment(
+        __().ref.int(-10), __().ref.float(0.32))).Get() == -9.68);
+}
+
+protected static function SubTest_Incrementing_String()
+{
+    Issue("String values aren't incremented correctly.");
+    TEST_ExpectTrue(Text(__().json.Increment(
+        __().text.FromString("Whatever"), __().text.FromString("revetahW")))
+            .ToString() == "WhateverrevetahW");
+    TEST_ExpectTrue(MutableText(__().json.Increment(
+        __().text.FromStringM("Whatever"), __().text.FromString("revetahW")))
+            .ToString() == "WhateverrevetahW");
+    TEST_ExpectTrue(Text(__().json.Increment(
+        __().text.FromString("Whatever"), __().text.FromStringM("revetahW")))
+            .ToString() == "WhateverrevetahW");
+    TEST_ExpectTrue(MutableText(__().json.Increment(
+        __().text.FromStringM("Whatever"), __().text.FromStringM("revetahW")))
+            .ToString() == "WhateverrevetahW");
+}
+
+protected static function SubTest_Incrementing_Array()
+{
+    local ArrayList array1, array2, result;
+
+    Issue("Array values aren't incremented correctly.");
+    array1 = __().collections.EmptyArrayList();
+    array2 = __().collections.EmptyArrayList();
+    array1.AddItem(__().box.int(5));
+    array2.AddItem(__().box.int(3));
+    array2.AddItem(__().box.int(-7));
+    result = ArrayList(__().json.Increment(array1, array2));
+    TEST_ExpectTrue(__().json.Print(result).ToString() == "[5,3,-7]");
+    TEST_ExpectTrue(result.GetItem(0) != array1.GetItem(0));
+    TEST_ExpectTrue(result.GetItem(1) != array2.GetItem(0));
+    TEST_ExpectTrue(result.GetItem(2) != array2.GetItem(1));
+
+    Issue("Incrementing array values incorrectly handles reference counts.");
+    //  +1 after copy, +2 after getters (before and here)
+    TEST_ExpectTrue(result.GetItem(0)._getRefCount() == 3);
+    TEST_ExpectTrue(result.GetItem(1)._getRefCount() == 3);
+    TEST_ExpectTrue(result.GetItem(2)._getRefCount() == 3);
+    TEST_ExpectTrue(array1._getRefCount() == 1);
+    TEST_ExpectTrue(array2._getRefCount() == 1);
+    TEST_ExpectTrue(result._getRefCount() == 1);
+}
+
+protected static function SubTest_Incrementing_Object()
+{
+    local HashTable table1, table2, result;
+
+    Issue("Object values aren't incremented correctly.");
+    table1 = __().collections.EmptyHashTable();
+    table2 = __().collections.EmptyHashTable();
+    table1.Setitem(P("A"), __().box.int(5));
+    table2.Setitem(P("B"), __().box.int(3));
+    table2.Setitem(P("C"), __().box.int(-7));
+    result = HashTable(__().json.Increment(table1, table2));
+    TEST_ExpectTrue(result.GetLength() == 3);
+    TEST_ExpectTrue(result.GetInt(P("A")) == 5);
+    TEST_ExpectTrue(result.GetInt(P("B")) == 3);
+    TEST_ExpectTrue(result.GetInt(P("C")) == -7);
+    TEST_ExpectTrue(result.GetItem(P("A")) != table1.GetItem(P("A")));
+    TEST_ExpectTrue(result.GetItem(P("B")) != table2.GetItem(P("B")));
+    TEST_ExpectTrue(result.GetItem(P("C")) != table2.GetItem(P("C")));
+
+    //  +1 after copy, +2 after getters (before and here)
+    Issue("Incrementing object values incorrectly handles reference counts.");
+    TEST_ExpectTrue(result.GetItem(P("A"))._getRefCount() == 3);
+    TEST_ExpectTrue(result.GetItem(P("B"))._getRefCount() == 3);
+    TEST_ExpectTrue(result.GetItem(P("C"))._getRefCount() == 3);
+    TEST_ExpectTrue(table1._getRefCount() == 1);
+    TEST_ExpectTrue(table2._getRefCount() == 1);
+    TEST_ExpectTrue(result._getRefCount() == 1);
+}
+
+protected static function SubTest_Incrementing_Incompatible()
+{
+    Issue("Incrementing with incompatible values doesn't produce `none`.");
+    SubSubTest_Incrementing_Incompatible_bool();
+    SubSubTest_Incrementing_Incompatible_int();
+    SubSubTest_Incrementing_Incompatible_float();
+    SubSubTest_Incrementing_Incompatible_text();
+    SubSubTest_Incrementing_Incompatible_arraylist();
+    SubSubTest_Incrementing_Incompatible_hashtable();
+}
+
+protected static function SubSubTest_Incrementing_Incompatible_bool()
+{
+    TEST_ExpectNone(__().json.Increment(
+        __().box.bool(true),
+        __().ref.int(32)));
+    TEST_ExpectNone(__().json.Increment(
+        __().box.bool(true),
+        __().ref.float(32.5)));
+    TEST_ExpectNone(__().json.Increment(
+        __().box.bool(true),
+        __().text.FromString("Hello there!")));
+    TEST_ExpectNone(__().json.Increment(
+        __().box.bool(true),
+        __().collections.EmptyArrayList()));
+    TEST_ExpectNone(__().json.Increment(
+        __().box.bool(true),
+        __().collections.EmptyHashTable()));
+}
+
+protected static function SubSubTest_Incrementing_Incompatible_int()
+{
+    TEST_ExpectNone(__().json.Increment(
+        __().box.int(3),
+        __().ref.bool(false)));
+    TEST_ExpectNone(__().json.Increment(
+        __().box.int(234),
+        __().text.FromString("Hello there!")));
+    TEST_ExpectNone(__().json.Increment(
+        __().box.int(2),
+        __().collections.EmptyArrayList()));
+    TEST_ExpectNone(__().json.Increment(
+        __().box.int(782),
+        __().collections.EmptyHashTable()));
+}
+
+protected static function SubSubTest_Incrementing_Incompatible_float()
+{
+    TEST_ExpectNone(__().json.Increment(
+        __().box.float(3),
+        __().ref.bool(false)));
+    TEST_ExpectNone(__().json.Increment(
+        __().box.float(234),
+        __().text.FromString("Hello there!")));
+    TEST_ExpectNone(__().json.Increment(
+        __().box.float(2),
+        __().collections.EmptyArrayList()));
+    TEST_ExpectNone(__().json.Increment(
+        __().box.float(782),
+        __().collections.EmptyHashTable()));
+}
+
+protected static function SubSubTest_Incrementing_Incompatible_text()
+{
+    TEST_ExpectNone(__().json.Increment(
+        __().text.FromString("yo"),
+        __().ref.bool(true)));
+    TEST_ExpectNone(__().json.Increment(
+        __().text.FromString("yo"),
+        __().ref.int(32)));
+    TEST_ExpectNone(__().json.Increment(
+        __().text.FromString("yo"),
+        __().ref.float(32.5)));
+    TEST_ExpectNone(__().json.Increment(
+        __().text.FromString("yo"),
+        __().collections.EmptyArrayList()));
+    TEST_ExpectNone(__().json.Increment(
+        __().text.FromString("yo"),
+        __().collections.EmptyHashTable()));
+}
+
+protected static function SubSubTest_Incrementing_Incompatible_arraylist()
+{
+    TEST_ExpectNone(__().json.Increment(
+        __().collections.EmptyArrayList(),
+        __().ref.bool(true)));
+    TEST_ExpectNone(__().json.Increment(
+        __().collections.EmptyArrayList(),
+        __().ref.int(32)));
+    TEST_ExpectNone(__().json.Increment(
+        __().collections.EmptyArrayList(),
+        __().ref.float(32.5)));
+    TEST_ExpectNone(__().json.Increment(
+        __().collections.EmptyArrayList(),
+        __().text.FromString("Not a collection!")));
+    TEST_ExpectNone(__().json.Increment(
+        __().collections.EmptyArrayList(),
+        __().collections.EmptyHashTable()));
+}
+
+protected static function SubSubTest_Incrementing_Incompatible_hashtable()
+{
+    TEST_ExpectNone(__().json.Increment(
+        __().collections.EmptyHashTable(),
+        __().ref.bool(true)));
+    TEST_ExpectNone(__().json.Increment(
+        __().collections.EmptyHashTable(),
+        __().ref.int(32)));
+    TEST_ExpectNone(__().json.Increment(
+        __().collections.EmptyHashTable(),
+        __().ref.float(32.5)));
+    TEST_ExpectNone(__().json.Increment(
+        __().collections.EmptyHashTable(),
+        __().text.FromString("Not a collection!")));
+    TEST_ExpectNone(__().json.Increment(
+        __().collections.EmptyHashTable(),
+        __().collections.EmptyArrayList()));
+}
+
 defaultproperties
 {
     caseName = "JSON"

sources/Users/ACommandUserGroups.uc

@@ -41,21 +41,8 @@ protected function BuildData(CommandDataBuilder builder)
     builder.SubCommand(P("remove"))
         .Describe(P("Removes a group"))
         .ParamText(P("group_name"));
-    builder.SubCommand(P("adduser"))
-        .Describe(P("Adds new user to the group. Allows to also optionally"
-            @ "specify annotation (human-readable name) that can be thought of"
-            @ "as a {$TextEmphasis comment}."))
-        .ParamText(P("group_name"))
-        .ParamText(P("user_id"))
-        .OptionalParams()
-        .ParamText(P("annotation"));
-    builder.SubCommand(P("removeuser"))
-        .Describe(P("Removes user from the group. User can be specified by both"
-            @ "user's id or annotation, with id taking priority."))
-        .ParamText(P("group_name"))
-        .ParamText(P("user_name"));
     builder.SubCommand(P("addplayer"))
-        .Describe(P("Adds new user to the group, specified by the player"
+        .Describe(F("Adds new user to the group, specified by the player"
             @ "selector. Can add several players at once."
             @ "Allows to also optionally specify annotation"
             @ "(human-readable name) that can be thought of as"
@@ -70,6 +57,19 @@ protected function BuildData(CommandDataBuilder builder)
             @ "Can remove several players at once."))
         .ParamText(P("group_name"))
         .ParamPlayers(P("player_selector"));
+    builder.SubCommand(P("adduser"))
+        .Describe(F("Adds new user to the group. Allows to also optionally"
+            @ "specify annotation (human-readable name) that can be thought of"
+            @ "as a {$TextEmphasis comment}."))
+        .ParamText(P("group_name"))
+        .ParamText(P("user_id"))
+        .OptionalParams()
+        .ParamText(P("annotation"));
+    builder.SubCommand(P("removeuser"))
+        .Describe(P("Removes user from the group. User can be specified by both"
+            @ "user's id or annotation, with id taking priority."))
+        .ParamText(P("group_name"))
+        .ParamText(P("user_name"));
     builder.Option(P("force"))
         .Describe(P("Allows to force usage of invalid user IDs."));
 }
@@ -89,6 +89,7 @@ protected function Executed(CallData arguments, EPlayer instigator)
     //  An array of players that can be specified for some commands
     players     = arguments.parameters.GetArrayList(P("player_selector"));
     groups      = arguments.parameters.GetArrayList(P("groups"));
+    forceOption = arguments.options.HasKey(P("force"));
     if (arguments.subCommandName.IsEmpty()) {
         DisplayUserGroups();
     }

sources/Users/PersistentData/Events/PersistentDataManager_OnPersistentDataReady_Signal.uc

@@ -0,0 +1,40 @@
+/**
+ *  Signal class for `PersistentDataManager`'s `OnPersistentDataReady()` signal.
+ *      Copyright 2023 Anton Tarasenko
+ *------------------------------------------------------------------------------
+ * This file is part of Acedia.
+ *
+ * Acedia is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Acedia is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Acedia.  If not, see <https://www.gnu.org/licenses/>.
+ */
+class PersistentDataManager_OnPersistentDataReady_Signal extends Signal
+    dependson(DBConnection);
+
+public final function Emit(UserID id, bool online)
+{
+    local Slot nextSlot;
+    StartIterating();
+    nextSlot = GetNextSlot();
+    while (nextSlot != none)
+    {
+        PersistentDataManager_OnPersistentDataReady_Slot(nextSlot)
+            .connect(id, online);
+        nextSlot = GetNextSlot();
+    }
+    CleanEmptySlots();
+}
+
+defaultproperties
+{
+    relatedSlotClass = class'PersistentDataManager_OnPersistentDataReady_Slot'
+}

sources/Users/PersistentData/Events/PersistentDataManager_OnPersistentDataReady_Slot.uc

@@ -0,0 +1,41 @@
+/**
+ *  Slot class for `PersistentDataManager`'s `OnPersistentDataReady()` signal.
+ *      Copyright 2023 Anton Tarasenko
+ *------------------------------------------------------------------------------
+ * This file is part of Acedia.
+ *
+ * Acedia is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Acedia is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Acedia.  If not, see <https://www.gnu.org/licenses/>.
+ */
+class PersistentDataManager_OnPersistentDataReady_Slot extends Slot
+    dependson(DBConnection);
+
+delegate connect(UserID id, bool online)
+{
+    DummyCall();
+}
+
+protected function Constructor()
+{
+    connect = none;
+}
+
+protected function Finalizer()
+{
+    super.Finalizer();
+    connect = none;
+}
+
+defaultproperties
+{
+}

sources/Users/PersistentData/PersistentDataManager.uc

@@ -0,0 +1,407 @@
+/**
+ *  This tool is for simplifying writing and reading persistent user data.
+ *  All it requires is a setup of database + json pointer to data and it will
+ *  take care of data caching and database connection.
+ *      Copyright 2023 Anton Tarasenko
+ *------------------------------------------------------------------------------
+ * This file is part of Acedia.
+ *
+ * Acedia is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Acedia is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Acedia.  If not, see <https://www.gnu.org/licenses/>.
+ */
+class PersistentDataManager extends AcediaObject;
+
+/**
+ *  # `PersistentDataManager`
+ *
+ *  This tool is for simplifying writing and reading persistent user data.
+ *  All it requires is a setup of database + json pointer to data and it will
+ *  take care of data caching and database connection.
+ *
+ *  ## Usage
+ *
+ *      Create an instance and use `Setup()` to connect to the database with
+ *  persistent data. You can use `Setup()` again on the same object to setup
+ *  a different database as a source. All data will be automatically reloaded.
+ *      After that you can use `GetPersistentData()`/`SetPersistentData()` to
+ *  read/write persistent data for the particular user.
+ *      Since loading data from the database takes time, you don't have an
+ *  immediate access to it.
+ *  But you can use `_.users.OnPersistentDataAvailable()` signal to track
+ *  whenever new user data from database becomes available. However, you can
+ *  start writing persistent data (and reading what you've wrote) at any time it
+ *  - these changes will be reapplied whenever data is actually loaded from
+ *  database.
+ *
+ *  ## Implementation
+ *
+ *      Implementation consists of simply creating `DBConnection` for every user
+ *  and storing them in the `HashTable` that maps user IDs into those
+ *  `DBConnection`s.
+ *      We also maintain a reverse map to figure out what `DBConnection` belongs
+ *  to what user when connection signals an update. We borrow the signal that
+ *  `UsersAPI` provides to inform everyone interested about which users
+ *  have updated.
+ */
+
+var private bool        initialized;
+var private Database    database;
+var private JSONPointer rootPointer;
+var private HashTable   userToConnection, connectionToUser;
+
+var private PersistentDataManager_OnPersistentDataReady_Signal onPersistentDataReadySignal;
+
+protected function Constructor()
+{
+    _.players.OnNewPlayer(self).connect = ConnectPersistentData;
+    onPersistentDataReadySignal = _.users._getOnReadySignal();
+}
+
+protected function Finalizer()
+{
+    Reset();
+    _.players.OnNewPlayer(self).Disconnect();
+}
+
+private final function Reset()
+{
+    _.memory.Free(database);
+    _.memory.Free(rootPointer);
+    _.memory.Free(userToConnection);
+    _.memory.Free(connectionToUser);
+    _.memory.Free(onPersistentDataReadySignal);
+    database                    = none;
+    rootPointer                 = none;
+    userToConnection            = none;
+    connectionToUser            = none;
+    onPersistentDataReadySignal = none;
+    initialized = false;
+}
+
+/**
+ *  Sets up database and location inside it as a source of users' persistent
+ *  data.
+ *
+ *  Must be successfully called at least once for the caller
+ *  `PersistentDataManager` to be usable.
+ *
+ *  @param  db          Database inside which persistent data is stored.
+ *  @param  location    Location inside specified database to the root of
+ *      persistent data.
+ *  @return `true` if setup was successful (requires both arguments to be not
+ *      `none`) and `false` otherwise.
+ */
+public final function bool Setup(Database db, JSONPointer location)
+{
+    if (db == none)         return false;
+    if (location == none)   return false;
+
+    Reset();
+    database = db;
+    database.NewRef();
+    rootPointer = location.Copy();
+    userToConnection = _.collections.EmptyHashTable();
+    connectionToUser = _.collections.EmptyHashTable();
+    //  Using `userToConnection` as an empty hash table, not related to its
+    //  actual meaning
+    database.IncrementData(location, userToConnection);
+    initialized = true;
+    return true;
+}
+
+/**
+ *  Reads specified named persistent data for the specified group.
+ *
+ *  @param  id          ID of the user to read persistent data from.
+ *  @param  groupName   Group to which this persistent data belongs to.
+ *      Groups are used as namespaces to avoid duplicate persistent variables
+ *      between mods. If your mod needs several subgroups, its recommended to
+ *      use the same prefix for them, e.g. "MyAwesomeMod.economy" and
+ *      "MyAwesomeMod.enemies".
+ *  @param  dataName    Name of persistent data variable to read inside
+ *      `groupName` persistent data group. Not `none` value must be provided.
+ *  @param  data        Data to set as persistent value. Must be
+ *      JSON-compatible. If `none` is passed, returns the all data for
+ *      the given group.
+ *  @return Data read from the persistent variable. `none` in case of any kind
+ *      of failure.
+ */
+public final function AcediaObject GetPersistentData(
+    UserID              id,
+    BaseText            groupName,
+    optional BaseText   dataName)
+{
+    local AcediaObject  result;
+    local Text          textID;
+    local JSONPointer   location;
+    local DBConnection  relevantConnection;
+
+    if (!initialized)       return none;
+    if (id == none)         return none;
+    if (groupName == none)  return none;
+
+    textID = id.GetUniqueID();
+    relevantConnection = DBConnection(userToConnection.GetItem(textID));
+    textID.FreeSelf();
+    if (relevantConnection != none)
+    {
+        location = _.json.Pointer();
+        location.Push(groupName);
+        if (dataName != none) {
+            location.Push(dataName);
+        }
+        result = relevantConnection.ReadDataByJSON(location);
+        relevantConnection.FreeSelf();
+        location.FreeSelf();
+    }
+    return result;
+}
+
+/**
+ *  Writes specified named persistent data for the specified group.
+ *
+ *  @param  id          ID of the user to change persistent data of.
+ *  @param  groupName   Group to which this persistent data belongs to.
+ *      Groups are used as namespaces to avoid duplicate persistent variables
+ *      between mods. If your mod needs several subgroups, its recommended to
+ *      use the same prefix for them, e.g. "MyAwesomeMod.economy" and
+ *      "MyAwesomeMod.enemies".
+ *  @param  dataName    Name of persistent data variable to change inside
+ *      `groupName` persistent data group.
+ *  @param  data        Data to set as persistent value. Must be
+ *      JSON-compatible.
+ *  @return `true` if change succeeded in local cached version of database with
+ *      persistent values and `false` otherwise. Such local changes can
+ *      potentially be not applied to the actual database. But successful local
+ *      changes should persist for the game session.
+ */
+public final function bool WritePersistentData(
+    UserID          id,
+    BaseText        groupName,
+    BaseText        dataName,
+    AcediaObject    data)
+{
+    local bool          result;
+    local Text          textID;
+    local JSONPointer   location;
+    local DBConnection  relevantConnection;
+    local HashTable     emptyObject;
+
+    if (!initialized)       return false;
+    if (id == none)         return false;
+    if (groupName == none)  return false;
+    if (dataName == none)   return false;
+
+    textID = id.GetUniqueID();
+    relevantConnection = DBConnection(userToConnection.GetItem(textID));
+    textID.FreeSelf();
+    if (relevantConnection != none)
+    {
+        emptyObject = _.collections.EmptyHashTable();
+        location = _.json.Pointer();
+        location.Push(groupName);
+        relevantConnection.IncrementDataByJSON(location, emptyObject);
+        location.Push(dataName);
+        result = relevantConnection.WriteDataByJSON(location, data);
+        relevantConnection.FreeSelf();
+        location.FreeSelf();
+        emptyObject.FreeSelf();
+    }
+    return result;
+}
+
+/**
+ *  Increments specified named persistent data for the specified group.
+ *
+ *  @param  id          ID of the user to change persistent data of.
+ *  @param  groupName   Group to which this persistent data belongs to.
+ *      Groups are used as namespaces to avoid duplicate persistent variables
+ *      between mods. If your mod needs several subgroups, its recommended to
+ *      use the same prefix for them, e.g. "MyAwesomeMod.economy" and
+ *      "MyAwesomeMod.enemies".
+ *  @param  dataName    Name of persistent data variable to change inside
+ *      `groupName` persistent data group.
+ *  @param  data        Data by which to increment existing persistent value.
+ *      Must be JSON-compatible.
+ *  @return `true` if change succeeded in local cached version of database with
+ *      persistent values and `false` otherwise. Such local changes can
+ *      potentially be not applied to the actual database. But successful local
+ *      changes should persist for the game session.
+ */
+public final function bool IncrementPersistentData(
+    UserID          id,
+    BaseText        groupName,
+    BaseText        dataName,
+    AcediaObject    data)
+{
+    local bool          result;
+    local Text          textID;
+    local JSONPointer   location;
+    local DBConnection  relevantConnection;
+
+    if (!initialized)       return false;
+    if (id == none)         return false;
+    if (groupName == none)  return false;
+    if (dataName == none)   return false;
+
+    textID = id.GetUniqueID();
+    relevantConnection = DBConnection(userToConnection.GetItem(textID));
+    textID.FreeSelf();
+    if (relevantConnection != none)
+    {
+        location = _.json.Pointer();
+        location.Push(groupName).Push(dataName);
+        result = relevantConnection.IncrementDataByJSON(location, data);
+        relevantConnection.FreeSelf();
+        location.FreeSelf();
+    }
+    return result;
+}
+
+/**
+ *  Removes specified named persistent data for the specified group.
+ *
+ *  @param  id          ID of the user to remove persistent data of.
+ *  @param  groupName   Group to which this persistent data belongs to.
+ *      Groups are used as namespaces to avoid duplicate persistent variables
+ *      between mods. If your mod needs several subgroups, its recommended to
+ *      use the same prefix for them, e.g. "MyAwesomeMod.economy" and
+ *      "MyAwesomeMod.enemies".
+ *  @param  dataName    Name of persistent data variable to remove inside
+ *      `groupName` persistent data group.
+ *  @return `true` if removal succeeded in local cached version of database with
+ *      persistent values and `false` otherwise. Such local changes can
+ *      potentially be not applied to the actual database. But successful local
+ *      changes should persist for the game session.
+ */
+public final function bool RemovePersistentData(
+    UserID      id,
+    BaseText    groupName,
+    BaseText    dataName)
+{
+    local bool          result;
+    local Text          textID;
+    local JSONPointer   location;
+    local DBConnection  relevantConnection;
+
+    if (!initialized)       return false;
+    if (id == none)         return false;
+    if (groupName == none)  return false;
+    if (dataName == none)   return false;
+
+    textID = id.GetUniqueID();
+    relevantConnection = DBConnection(userToConnection.GetItem(textID));
+    textID.FreeSelf();
+    if (relevantConnection != none)
+    {
+        location = _.json.Pointer();
+        location.Push(groupName).Push(dataName);
+        result = relevantConnection.RemoveDataByJSON(location);
+        relevantConnection.FreeSelf();
+        location.FreeSelf();
+    }
+    return result;
+}
+
+/**
+ *  Connects and starts synchronizing persistent data for the given player.
+ *
+ *  @param  player  Player to synchronize persistent data for.
+ */
+public final function ConnectPersistentData(EPlayer player)
+{
+    local UserID playerID;
+
+    if (initialized && player != none)
+    {
+        playerID = player.GetUserID();
+        ConnectPersistentDataByID(playerID);
+        _.memory.Free(playerID);
+    }
+}
+
+/**
+ *  Connects and starts synchronizing persistent data for the player given by
+ *  their ID.
+ *
+ *  @param  id  User ID for which to synchronize persistent data from
+ *      the database.
+ */
+public final function ConnectPersistentDataByID(UserID id)
+{
+    local Text          textID;
+    local DBConnection  newConnection;
+
+    if (!initialized)   return;
+    if (id == none)     return;
+
+    textID = id.GetUniqueID();
+    if (userToConnection.HasKey(textID))
+    {
+        _.memory.Free(textID);
+        return;
+    }
+    rootPointer.Push(textID);
+    newConnection = DBConnection(_.memory.Allocate(class'DBConnection'));
+    newConnection.Initialize(database, rootPointer);
+    _.memory.Free(rootPointer.Pop());
+    newConnection.Connect();
+    userToConnection.SetItem(textID, newConnection);
+    connectionToUser.SetItem(newConnection, textID);
+    newConnection.OnStateChanged(self).connect = UserUpdated;
+    textID.FreeSelf();
+    newConnection.FreeSelf();
+}
+
+private final function UserUpdated(
+    DBConnection                    instance,
+    DBConnection.DBConnectionState  oldState,
+    DBConnection.DBConnectionState  newState)
+{
+    local UserID id;
+
+    if (!initialized)                               return;
+    if (newState == DBCS_Connecting)                return;
+    if (onPersistentDataReadySignal == none)        return;
+    if (!onPersistentDataReadySignal.IsAllocated()) return;
+
+    id = UserID(connectionToUser.GetItem(instance));
+    if (id != none)
+    {
+        onPersistentDataReadySignal.Emit(id, newState == DBCS_Connected);
+        id.FreeSelf();
+    }
+}
+
+/**
+ *  Attempts to start persistent data synchronization for all players currently
+ *  on the server.
+ */
+public final function LoadCurrentPlayers()
+{
+    local int               i;
+    local array<EPlayer>    currentPlayers;
+
+    if (initialized)
+    {
+        currentPlayers = _.players.GetAll();
+        for (i = 0; i < currentPlayers.length; i += 1) {
+            ConnectPersistentData(currentPlayers[i]);
+        }
+        _.memory.FreeMany(currentPlayers);
+    }
+}
+
+defaultproperties
+{
+}

sources/Users/User.uc

@@ -2,7 +2,7 @@
  *      Object that is supposed to store a persistent data about the
  *  certain player. That is data that will be remembered even after player
  *  reconnects or server changes map/restarts.
- *      Copyright 2020-2022 Anton Tarasenko
+ *      Copyright 2020-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -27,38 +27,40 @@ var private UserID  id;
 //  an easy reference in console commands
 var private int     key;
 
-//      If we failed to create user database skeleton - set this to `true`,
+var private HashTable sessionData;
-//  this will prevent us from making changes that might mess up database due to
+
-//  misconfiguration
+var private int                     persistentDataLifeVersion;
-var private bool        failedToCreateDatabaseSkeleton;
+var private PersistentDataManager   persistentData;
-//  Database where user's persistent data is stored
-var private Database    persistentDatabase;
-//  Pointer to this user's "settings" data in particular
-var private JSONPointer persistentSettingsPointer;
-//      Groups to which caller `User` belongs to.
-//      Every user always belongs to group "everyone", so it is never listed
-//  here.
-//      Local user groups are not available for modification and are only loaded
-//  from configs, so `userGroups` might duplicate groups from `localUserGroup`,
-//  allowing to add them to editable sources (database).
-//      Group names are stored in the lower register.
-var private array<Text> userGroups; // user groups loaded from database
-var private array<Text> localUserGroups; // user groups loaded from local files
-var private LoggerAPI.Definition warnNoPersistentDatabase;
-var private LoggerAPI.Definition infoPersistentDatabaseLoaded;
-var private LoggerAPI.Definition errCannotCreateSkeletonFor;
-var private LoggerAPI.Definition errCannotReadDB, errInvalidUserGroups;
 
 protected function Finalizer()
 {
     if (id != none) {
         id.FreeSelf();
     }
-    if (persistentSettingsPointer != none) {
+    id = none;
-        persistentSettingsPointer.FreeSelf();
+}
+
+private final function UpdatePersistentDataManager()
+{
+    local Users_Feature feature;
+
+    if (    persistentData != none
+        &&  persistentData.GetLifeVersion() != persistentDataLifeVersion)
+    {
+        persistentData = none;
+    }
+    if (persistentData == none)
+    {
+        feature =
+            Users_Feature(class'Users_Feature'.static.GetEnabledInstance());
+        if (feature != none) {
+            persistentData = feature.BorrowPersistentDataManager();
+        }
+        if (persistentData != none) {
+            persistentDataLifeVersion = persistentData.GetLifeVersion();
+        }
+        _.memory.Free(feature);
     }
-    id                          = none;
-    persistentSettingsPointer   = none;
 }
 
 /**
@@ -71,17 +73,11 @@ protected function Finalizer()
  */
 public final function Initialize(UserID initID, int initKey)
 {
-    local DBReadTask groupsReadingTask;
     id  = initID;
     key = initKey;
     if (initID != none) {
         initID.NewRef();
     }
-    //LoadLocalGroups();
-    /*groupsReadingTask = ReadPersistentData(P("Acedia"), P("UserGroups"));
-    if (groupsReadingTask != none) {
-        groupsReadingTask.connect = LoadDBGroups;
-    }*/
 }
 
 /**
@@ -107,402 +103,60 @@ public final function int GetKey()
     return key;
 }
 
-//  Loads locally defined groups from the "AcediaUserGroups.ini" config
-private final function LoadLocalGroups()
-{
-    local int           i, j;
-    local string        mySteamID;
-    local UserGroup     nextGroupConfig;
-    local array<string> nextUserArray;
-    local array<Text>   availableGroups;
-
-    if (id == none) {
-        return;
-    }
-    class'UserGroup'.static.Initialize();
-    mySteamID = _.text.IntoString(id.GetSteamID64String());
-    availableGroups = class'UserGroup'.static.AvailableConfigs();
-    //  Go over every group
-    for (i = 0; i < availableGroups.length; i += 1)
-    {
-        nextGroupConfig = UserGroup(
-            class'UserGroup'.static.GetConfigInstance(availableGroups[i]));
-        //  Add group as local if it has our ID recorded
-        nextUserArray = nextGroupConfig.user;
-        for (j = 0; j < nextUserArray.length; j += 1)
-        {
-            if (nextUserArray[j] == mySteamID)
-            {
-                localUserGroups[localUserGroups.length] =
-                    availableGroups[i].LowerCopy();
-            }
-        }
-        _.memory.Free(nextGroupConfig);
-    }
-    _.memory.FreeMany(availableGroups);
-}
-
-//  Loads groups defined in database with user data
-private final function LoadDBGroups(
-    Database.DBQueryResult  result,
-    AcediaObject            data,
-    Database                source)
-{
-    local int           i;
-    local MutableText   nextGroup;
-    local ArrayList     dbGroups;
-
-    if (result != DBR_Success)
-    {
-        _.logger.Auto(errCannotReadDB);
-        return;
-    }
-    _.memory.FreeMany(userGroups);
-    userGroups.length = 0;
-    dbGroups = ArrayList(data);
-    if (dbGroups == none)
-    {
-        if (data != none)
-        {
-            _.logger.Auto(errInvalidUserGroups);
-            _.memory.Free(data);
-        }
-        return;
-    }
-    for (i = 0; i < dbGroups.GetLength(); i += 1)
-    {
-        nextGroup = dbGroups.GetMutableText(i);
-        if (nextGroup == none) {
-            continue;
-        }
-        if (!class'UserGroup'.static.Exists(nextGroup))
-        {
-            nextGroup.FreeSelf();
-            continue;
-        }
-        userGroups[userGroups.length] = nextGroup.IntoText();
-    }
-    dbGroups.FreeSelf();
-}
-
-//  Save current user groups into the user data database
-private final function UpdateDBGroups()
-{
-    local ArrayList newDBData;
-
-    newDBData = _.collections.NewArrayList(userGroups);
-    WritePersistentData(P("Acedia"), P("UserGroups"), newDBData);
-    newDBData.FreeSelf();
-}
-
-/**
- *  Adds caller user into new group, specified by `newGroup`.
- *  This group must exist for the method to succeed.
- *
- *  @param  newGroup    Name of the group to add caller `User` into.
- */
-public final function AddGroup(Text newGroup)
-{
-    local int i;
-
-    if (newGroup == none)                           return;
-    if (class'UserGroup'.static.Exists(newGroup))   return;
-
-    for (i = 0; i < userGroups.length; i += 1)
-    {
-        if (newGroup.Compare(userGroups[i], SCASE_INSENSITIVE)) {
-            return;
-        }
-    }
-    userGroups[userGroups.length] = newGroup.LowerCopy();
-    UpdateDBGroups();
-}
-
-/**
- *  Removes caller user from the given group `groupToRemove`.
- *
- *  @param  groupToRemove   Name of the group to remove caller `User` from.
- *  @return `true` if user was actually removed from the group and `false`
- *      otherwise (group doesn't exist or user didn't belong to it).
- */
-public final function bool RemoveGroup(Text groupToRemove)
-{
-    local int i;
-
-    if (groupToRemove == none) {
-        return false;
-    }
-    for (i = 0; i < userGroups.length; i += 1)
-    {
-        if (groupToRemove.Compare(userGroups[i], SCASE_INSENSITIVE))
-        {
-            userGroups[i].FreeSelf();
-            userGroups.Remove(i, 1);
-            UpdateDBGroups();
-            return true;
-        }
-    }
-    return false;
-}
-
 /**
- *  Checks whether caller `User` belongs to the group specified by
+ *  Returns persistent data for the caller user. Data is specified by the its
- *  `groupToCheck`.
+ *  name along with the name of the data group it is stored in.
  *
- *  @param  groupToCheck    Name of the group to check for whether caller `User`
+ *  @param  groupName   Name of the group to get data from. Cannot be `none`.
- *      belongs to it.
+ *  @param  dataName    Name of the data to return. If `none` value is provided,
- *  @return `true` if caller `User` belongs to the group `groupToCheck` and
+ *      all the data in specified group will be returned.
- *      `false` otherwise.
+ *  @return Requested data, `none` in case of failure (i.e. data is missing).
  */
-public final function bool IsInGroup(Text groupToCheck)
+public final function AcediaObject GetPersistentData(
-{
-    local int i;
-
-    if (groupToCheck == none) {
-        return false;
-    }
-    for (i = 0; i < userGroups.length; i += 1)
-    {
-        if (groupToCheck.Compare(userGroups[i], SCASE_INSENSITIVE)) {
-            return true;
-        }
-    }
-    return false;
-}
-
-/**
- *  Returns array with names of all groups to which caller user belongs to.
- *
- *  @return Array of names of the groups that caller user belongs to.
- *      Guaranteed to not contain duplicates or `none` values.
- */
-public final function array<Text> GetGroups()
-{
-    local int           i, j;
-    local bool          duplicate;
-    local array<Text>   result;
-
-    for (i = 0; i < localUserGroups.length; i += 1) {
-        result[result.length] = localUserGroups[i].Copy();
-    }
-    for (i = 0; i < userGroups.length; i += 1)
-    {
-        duplicate = false;
-        //  Check `userGroups[i]` for being a duplicate from `localUserGroups`
-        for (j = 0; j < localUserGroups.length; j += 1)
-        {
-            //  No need for `SCASE_INSENSITIVE`, since user group names
-            //  are stored in lower case
-            if (userGroups[i].Compare(localUserGroups[j]))
-            {
-                duplicate = true;
-                break;
-            }
-        }
-        if (!duplicate) {
-            result[result.length] = userGroups[i].Copy();
-        }
-    }
-    return result;
-}
-
-/**
- *  Reads user's persistent data saved inside group `groupName`, saving it into
- *  a collection using mutable data types.
- *  Only should be used if `_.users.PersistentStorageExists()` returns `true`.
- *
- *  @param  groupName   Name of the group these settings belong to.
- *      This exists to help reduce name collisions between different mods.
- *      Acedia stores all its settings under "Acedia" group. We suggest that you
- *      pick at least one name to use for your own mods.
- *      It should be unique enough to not get picked by others - "weapons" is
- *      a bad name, while "CoolModMastah79" is actually a good pick.
- *  @return Task object for reading specified persistent data from the database.
- *      For more info see `Database.ReadData()` method.
- *      Guaranteed to not be `none` iff
- *      `_.users.PersistentStorageExists() == true`.
- */
-public final function DBReadTask ReadGroupOfPersistentData(BaseText groupName)
-{
-    local DBReadTask task;
-
-    if (groupName == none)          return none;
-    if (!SetupDatabaseVariables())  return none;
-
-    persistentSettingsPointer.Push(groupName);
-    task = persistentDatabase.ReadData(persistentSettingsPointer, true);
-    _.memory.Free(persistentSettingsPointer.Pop());
-    return task;
-}
-
-/**
- *  Reads user's persistent data saved under name `dataName`, saving it into
- *  a collection using mutable data types.
- *  Only should be used if `_.users.PersistentStorageExists()` returns `true`.
- *
- *  @param  groupName   Name of the group these settings belong to.
- *      This exists to help reduce name collisions between different mods.
- *      Acedia stores all its settings under "Acedia" group. We suggest that you
- *      pick at least one name to use for your own mods.
- *      It should be unique enough to not get picked by others - "weapons" is
- *      a bad name, while "CoolModMastah79" is actually a good pick.
- *  @param  dataName    Any name, from under which settings you are interested
- *      (inside `groupName` group) should be read.
- *  @return Task object for reading specified persistent data from the database.
- *      For more info see `Database.ReadData()` method.
- *      Guaranteed to not be `none` iff
- *      `_.users.PersistentStorageExists() == true`.
- */
-public final function DBReadTask ReadPersistentData(
     BaseText groupName,
     BaseText dataName)
 {
-    local DBReadTask task;
+    local AcediaObject  result;
-
+    local UserID        myID;
-    if (groupName == none)          return none;
-    if (dataName == none)           return none;
-    if (!SetupDatabaseVariables())  return none;
 
-    persistentSettingsPointer.Push(groupName).Push(dataName);
+    UpdatePersistentDataManager();
-    task = persistentDatabase.ReadData(persistentSettingsPointer, true);
+    if (persistentData == none) {
-    _.memory.Free(persistentSettingsPointer.Pop());
+        return none;
-    _.memory.Free(persistentSettingsPointer.Pop());
+    }
-    return task;
+    myID = GetID();
+    result = persistentData.GetPersistentData(myID, groupname, dataName);
+    _.memory.Free(myID);
+    return result;
 }
 
 /**
- *  Writes user's persistent data under name `dataName`.
+ *  Changes persistent data for the caller user. Data to change is specified by
- *  Only should be used if `_.users.PersistentStorageExists()` returns `true`.
+ *  the its name along with the name of the data group it is stored in.
  *
- *  @param  groupName   Name of the group these settings belong to.
+ *  @param  groupName   Name of the group to get data from. Cannot be `none`.
- *      This exists to help reduce name collisions between different mods.
+ *  @param  dataName    Name of the data to return. Cannot be `none`.
- *      Acedia stores all its settings under "Acedia" group. We suggest that you
+ *  @param  data        New data to record.
- *      pick at least one name to use for your own mods.
+ *  @return `true` in case operation was successful and `false` otherwise.
- *      It should be unique enough to not get picked by others - "weapons" is
- *      a bad name, while "CoolModMastah79" is actually a good pick.
- *  @param  dataName    Any name, under which settings you are interested
- *      (inside `groupName` group) should be written.
- *  @param  data        JSON-compatible (see `_.json.IsCompatible()`) data that
- *      should be written into database.
- *  @return Task object for writing specified persistent data into the database.
- *      For more info see `Database.WriteData()` method.
- *      Guarantee to not be `none` iff
- *      `_.users.PersistentStorageExists() == true`.
  */
-public final function DBWriteTask WritePersistentData(
+public final function bool SetPersistentData(
     BaseText        groupName,
     BaseText        dataName,
     AcediaObject    data)
 {
-    local DBWriteTask   task;
+    local bool      result;
-    local HashTable     emptyObject;
+    local UserID    myID;
-
-    if (groupName == none)          return none;
-    if (dataName == none)           return none;
-    if (!SetupDatabaseVariables())  return none;
-
-    emptyObject = _.collections.EmptyHashTable();
-    persistentSettingsPointer.Push(groupName);
-    persistentDatabase.IncrementData(persistentSettingsPointer, emptyObject);
-    persistentSettingsPointer.Push(dataName);
-    task = persistentDatabase.WriteData(persistentSettingsPointer, data);
-    _.memory.Free(persistentSettingsPointer.Pop());
-    _.memory.Free(persistentSettingsPointer.Pop());
-    _.memory.Free(emptyObject);
-    return task;
-}
-
-//  Setup database `persistentDatabase` and pointer to this user's data
-//  `persistentSettingsPointer`.
-//  Return `true` if these variables were setup (during this call or before)
-//  and `false` otherwise.
-private function bool SetupDatabaseVariables()
-{
-    local Text userDataLink;
-    local Text userTextID;
-
-    if (failedToCreateDatabaseSkeleton)     return false;
-    if (persistentDatabase != none)         return true;
-    if (id == none || !id.IsInitialized())  return false;
 
-    //  Check if database was even specified
+    UpdatePersistentDataManager();
-    persistentDatabase = _.users.GetPersistentDatabase();
+    if (persistentData == none) {
-    if (persistentDatabase == none)
-    {
-        _.logger.Auto(warnNoPersistentDatabase);
         return false;
     }
-    //  Try making skeleton database
+    myID = GetID();
-    userTextID      = id.GetSteamID64String();
+    result = persistentData
-    userDataLink    = _.users.GetPersistentDataLink();
+        .WritePersistentData(myID, groupname, dataName, data);
-    persistentSettingsPointer = __core().db.GetPointer(userDataLink);
+    _.memory.Free(myID);
-    persistentSettingsPointer.Push(P("PerUserData"));
+    return result;
-    persistentSettingsPointer.Push(userTextID);
-    MakeSkeletonUserDatabase(userTextID, persistentSettingsPointer);
-    persistentSettingsPointer.Push(P("settings"));
-    userTextID.FreeSelf();
-    _.memory.Free(userDataLink);
-    return true;
-}
-
-private function MakeSkeletonUserDatabase(
-    Text        userTextID,
-    JSONPointer userDataPointer)
-{
-    local HashTable skeleton, emptyObject;
-
-    //  Construct skeleton object
-    skeleton    = _.collections.EmptyHashTable();
-    emptyObject = _.collections.EmptyHashTable();
-    skeleton.SetItem(P("Settings"), emptyObject);
-    skeleton.SetItem(P("Statistics"), emptyObject);
-    //  Try adding the skeleton object
-    persistentDatabase
-        .IncrementData(userDataPointer, skeleton)
-        .connect = ReportSkeletonCreationResult;
-    //  Release skeleton objects
-    skeleton.FreeSelf();
-    emptyObject.FreeSelf();
-}
-
-private function ReportSkeletonCreationResult(
-    Database.DBQueryResult  result,
-    Database                source)
-{
-    local Text userTextID;
-    local Text userDataLink;
-
-    userTextID      = id.GetSteamID64String();
-    userDataLink    = _.users.GetPersistentDataLink();
-    if (result == DBR_Success)
-    {
-        _.logger.Auto(infoPersistentDatabaseLoaded)
-            .Arg(userTextID)
-            .Arg(userDataLink);
-    }
-    else
-    {
-        _.logger.Auto(errCannotCreateSkeletonFor)
-            .Arg(userTextID)
-            .Arg(userDataLink);
-        failedToCreateDatabaseSkeleton = true;
-        _.memory.Free(persistentDatabase);
-        _.memory.Free(persistentSettingsPointer);
-        persistentDatabase          = none;
-        persistentSettingsPointer   = none;
-    }
-    _.memory.Free(userTextID);
-    _.memory.Free(userDataLink);
 }
 
-//  Load groups from db data only, inside the `UserAPI`
-//  Get rid of the "AcediaUserGroups.ini"
-//  Make command for editing user groups
 defaultproperties
 {
-    warnNoPersistentDatabase        = (l=LOG_Error,m="No persistent user database available.")
-    infoPersistentDatabaseLoaded    = (l=LOG_Info,m="Persistent user database was setup for user \"%1\" (using database link \"%2\").")
-    errCannotCreateSkeletonFor      = (l=LOG_Error,m="Failed to create persistent user database skeleton for user \"%1\" (using database link \"%2\"). User data functionality won't function properly.")
-    errCannotReadDB                 = (l=LOG_Error,m="Failed to read user groups from persistent user database.")
-    errInvalidUserGroups            = (l=LOG_Error,m="Invalid data is written as user groups array inside persistent user database.")
 }

sources/Users/UserAPI.uc

@@ -1,6 +1,6 @@
 /**
  *      API that allows easy access to `User` persistent data and `UserID`s.
- *      Copyright 2020-2022 Anton Tarasenko
+ *      Copyright 2020-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -21,24 +21,42 @@ class UserAPI extends AcediaObject
     dependson(Users_Feature)
     config(AcediaSystem);
 
-var private config string userdataDBLink;
-
 //  Active `Users_Feature`, remember it along with life version to avoid
 //  taking up a reference
 var private int             usersFeatureLifeVersion;
 var private Users_Feature   usersFeature;
 
-//  Database where user's data (persistent data and user groups) is stored
+var private int                     persistentDataLifeVersion;
-var private Database persistentDatabase;
+var private PersistentDataManager   persistentData;
 
-var private LoggerAPI.Definition warnNoPersistentDatabaseLink;
+var private PersistentDataManager_OnPersistentDataReady_Signal onPersistentDataReadySignal;
-var private LoggerAPI.Definition errNoPersistentDatabase;
-var private LoggerAPI.Definition errCannotCreateSkeletonFor;
-var private LoggerAPI.Definition infoPersistentDatabaseLoaded;
 
-protected function Constructor()
+/**
+ *  Signal that will be emitted whenever we get an update on connection status
+ *  to the database, where persistent data for UserID is stored. This can
+ *  be updated several times in cases like `Users_Feature` being rebooted or
+ *  losing connection to the database.
+ *
+ *  [Signature]
+ *  void <slot>(UserID id, bool online)
+ *
+ *  @param  id      ID of the user, for whom status of persistent data got
+ *      updated.
+ *  @param  online  Is connection to the database online? If this flag is set to
+ *      `false` - an local, session-only storage will be used instead.
+ */
+/* SIGNAL */
+public final function PersistentDataManager_OnPersistentDataReady_Slot OnEditResult(
+    AcediaObject receiver)
+{
+    return PersistentDataManager_OnPersistentDataReady_Slot(
+        onPersistentDataReadySignal.NewSlot(receiver));
+}
+
+//  DO NOT CALL MANUALLY
+public function PersistentDataManager_OnPersistentDataReady_Signal _getOnReadySignal()
 {
-    //SetupUserDataDatabase();
+    return onPersistentDataReadySignal;
 }
 
 //  DO NOT CALL MANUALLY
@@ -58,111 +76,13 @@ public function _reloadFeature()
     _.memory.Free(usersFeature);
 }
 
-//  Loads persistent user database, specified by the AcediaCore's config and
+protected function Constructor()
-//  creates a basic skeleton for storing its data
-private function SetupUserDataDatabase()
-{
-    local Text          persistentDataLink;
-    local JSONPointer   persistentDataPointer;
-    local HashTable     skeleton, emptyObject;
-
-    if (persistentDatabase != none) {
-        return;
-    }
-    //  Check if database was even specified
-    persistentDataLink = GetPersistentDataLink();
-    if (persistentDataLink.IsEmpty())
-    {
-        _.logger.Auto(warnNoPersistentDatabaseLink);
-        persistentDataLink.FreeSelf();
-        return;
-    }
-    //  If link was specified - try loading database from it
-    persistentDatabase = __core().db.Load(persistentDataLink);
-    if (persistentDatabase == none)
-    {
-        _.logger.Auto(errNoPersistentDatabase).Arg(persistentDataLink);
-        return;
-    }
-    //  Write skeleton database's skeleton
-    skeleton    = _.collections.EmptyHashTable();
-    emptyObject = _.collections.EmptyHashTable();
-    skeleton.SetItem(P("Groups"), emptyObject);
-    skeleton.SetItem(P("PerUserData"), emptyObject);
-    persistentDataPointer = __core().db.GetPointer(persistentDataLink);
-    persistentDatabase
-        .IncrementData(persistentDataPointer, skeleton)
-        .connect = ReportSkeletonCreationResult;
-    skeleton.FreeSelf();
-    emptyObject.FreeSelf();
-    persistentDataLink.FreeSelf();
-    _.memory.Free(persistentDataPointer);
-}
-
-private function ReportSkeletonCreationResult(
-    Database.DBQueryResult  result,
-    Database                source)
-{
-    local Text persistentDataLink;
-
-    persistentDataLink = GetPersistentDataLink();
-    if (result == DBR_Success) {
-        _.logger.Auto(infoPersistentDatabaseLoaded).Arg(persistentDataLink);
-    }
-    else
-    {
-        _.logger.Auto(errCannotCreateSkeletonFor).Arg(persistentDataLink);
-        _.memory.Free(persistentDatabase);
-        persistentDatabase = none;
-    }
-    _.memory.Free(persistentDataLink);
-}
-
-/**
- *  Returns reference to the database of user records that Acedia was
- *  set up to use.
- *
- *  `UserDatabase` is for storing a set of users that joined the game during
- *  the session, for database that stores persistent user data
- *  @see `GetPersistentDatabase()`.
- *
- *  @return Main `UserDatabase` that Acedia currently uses to load and
- *      store user information. Guaranteed to be a valid non-`none` reference.
- */
-public final function UserDatabase GetDatabase()
-{
-    return class'UserDatabase'.static.GetInstance();
-}
-
-/**
- *  Returns reference to the database of user records that Acedia was
- *  set up to use.
- *
- *  `Database` returned by this method stores persistent user data, for
- *  the database of users that joined during the current game session
- *  @see `GetDatabase()`.
- *
- *  @return Main `UserDatabase` that Acedia currently uses to load and
- *      store user information. Guaranteed to be a valid non-`none` reference.
- */
-public final function Database GetPersistentDatabase()
-{
-    if (persistentDatabase != none) {
-        persistentDatabase.NewRef();
-    }
-    return persistentDatabase;
-}
-
-/**
- *  Returns configured database link to the JSON object in which users' data
- *  is stored.
- *
- *  @return Database link to the JSON object in which users' data is stored.
- *      Guaranteed to not be `none`.
- */
-public final function Text GetPersistentDataLink()
 {
-    return _.text.FromString(userdataDBLink);
+    onPersistentDataReadySignal =
+        PersistentDataManager_OnPersistentDataReady_Signal(
+            _.memory.Allocate(
+                class'PersistentDataManager_OnPersistentDataReady_Signal')
+        );
 }
 
 /**
@@ -176,9 +96,12 @@ public final function Text GetPersistentDataLink()
  *  @return `true` if database for users' persistent data storage exists and
  *      `false` otherwise.
  */
-public final function bool PersistentStorageExists()
+public final function bool IsPersistentStorageActive()
 {
-    return (persistentDatabase != none);
+    if (usersFeature != none) {
+        return (usersFeature.BorrowPersistentDataManager() != none);
+    }
+    return false;
 }
 
 /**
@@ -1527,9 +1450,4 @@ public final function bool IsUserGroupDataLoaded()
 
 defaultproperties
 {
-    userdataDBLink = "[local]database:/users"
-    warnNoPersistentDatabaseLink    = (l=LOG_Warning,m="No persistent user database link is setup. No persistent user data or user groups will be available. Setup `userDataDBLink` inside \"AcediaSystem.ini\".")
-    errCannotCreateSkeletonFor      = (l=LOG_Error,m="Failed to create persistent database skeleton for connected database with link \"%1\". User data functionality won't function properly.")
-    errNoPersistentDatabase         = (l=LOG_Error,m="Failed to connect to persistent user database with link \"%1\".")
-    infoPersistentDatabaseLoaded    = (l=LOG_Info,m="Connected to persistent user database with link \"%1\".")
 }

sources/Users/UserDatabase.uc

@@ -1,7 +1,7 @@
 /**
  *  Simple user database for Acedia.
  *  Only stores data for a session, map or server restarts will clear it.
- *      Copyright 2020 Anton Tarasenko
+ *      Copyright 2020-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -23,7 +23,7 @@ class UserDatabase extends AcediaObject
 
 //  This is used as a global variable only (`default.activeDatabase`) to store
 //  a reference to main database for persistent data, used by Acedia.
-var public UserDatabase    activeDatabase;
+var public UserDatabase     activeDatabase;
 //  `User` records that were stored this session
 var private array<User>     sessionUsers;
 //  `UserID`s generated during this session.
@@ -90,7 +90,7 @@ public final function UserID FetchUserID(BaseText idHash)
     if (newUserID.IsInitialized())
     {
         storedUserIDs[storedUserIDs.length] = newUserID;
-        newUserID.newRef();
+        newUserID.NewRef();
         return newUserID;
     }
     _.memory.Free(steamID.steamID64);
@@ -112,13 +112,16 @@ public final function User FetchUser(UserID userID)
     local User  newUser;
     for (i = 0; i < sessionUsers.length; i += 1)
     {
-        if (sessionUsers[i].GetID().IsEqual(userID)) {
+        if (sessionUsers[i].GetID().IsEqual(userID))
+        {
+            sessionUsers[i].NewRef();
             return sessionUsers[i];
         }
     }
     newUser = User(__().memory.Allocate(class'User'));
     newUser.Initialize(userID, sessionUsers.length + 1);
     sessionUsers[sessionUsers.length] = newUser;
+    newUser.NewRef();
     return newUser;
 }
 
@@ -135,7 +138,9 @@ public final function User FetchUserByKey(int userKey)
     local int i;
     for (i = 0; i < sessionUsers.length; i += 1)
     {
-        if (sessionUsers[i].GetKey() == userKey) {
+        if (sessionUsers[i].GetKey() == userKey)
+        {
+            sessionUsers[i].NewRef();
             return sessionUsers[i];
         }
     }

sources/Users/Users.uc

@@ -21,8 +21,10 @@ class Users extends FeatureConfig
     perobjectconfig
     config(AcediaUsers);
 
-var public config bool          useDatabase;
+var public config bool          usePersistentData;
-var public config string        databaseLink;
+var public config string        persistentDataDatabaseLink;
+var public config bool          useDatabaseForGroupsData;
+var public config string        groupsDatabaseLink;
 var public config array<string> localUserGroup;
 
 protected function HashTable ToData()
@@ -32,8 +34,10 @@ protected function HashTable ToData()
     local ArrayList userGroupList;
 
     data = __().collections.EmptyHashTable();
-    data.SetBool(P("useDatabase"), useDatabase, false);
+    data.SetBool(P("usePersistentData"), usePersistentData);
-    data.SetString(P("databaseLink"), databaseLink);
+    data.SetString(P("persistentDataDatabaseLink"), persistentDataDatabaseLink);
+    data.SetBool(P("useDatabaseForGroupsData"), useDatabaseForGroupsData);
+    data.SetString(P("groupsDatabaseLink"), groupsDatabaseLink);
     userGroupList = _.collections.EmptyArrayList();
     for (i = 0; i < localUserGroup.length; i += 1) {
         userGroupList.AddString(localUserGroup[i]);
@@ -51,10 +55,14 @@ protected function FromData(HashTable source)
     if (source == none) {
         return;
     }
-    useDatabase     = source.GetBool(P("useDatabase"));
+    usePersistentData           = source.GetBool(P("usePersistentData"));
-    databaseLink    = source.GetString(
+    persistentDataDatabaseLink  = source.GetString(
-        P("databaseLink"),
+        P("persistentDataDatabaseLink"),
-        "[local]database:/users");
+        "[local]database:/persistent_data");
+    useDatabaseForGroupsData    = source.GetBool(P("useDatabaseForGroupsData"));
+    groupsDatabaseLink          = source.GetString(
+        P("groupsDatabaseLink"),
+        "[local]database:/groups_data");
     userGroupList   = source.GetArrayList(P("userGroups"));
     localUserGroup.length = 0;
     if (userGroupList == none) {
@@ -68,8 +76,10 @@ protected function FromData(HashTable source)
 
 protected function DefaultIt()
 {
-    useDatabase     = false;
+    usePersistentData           = false;
-    databaseLink    = "[local]database:/users";
+    persistentDataDatabaseLink  = "[local]database:/persistent_data";
+    useDatabaseForGroupsData    = false;
+    groupsDatabaseLink          = "[local]database:/groups_data";
     localUserGroup.length = 0;
     localUserGroup[0] = "admin";
     localUserGroup[1] = "moderator";
@@ -79,8 +89,10 @@ protected function DefaultIt()
 defaultproperties
 {
     configName = "AcediaUsers"
-    useDatabase = false
+    usePersistentData           = false
-    databaseLink = "[local]database:/users"
+    persistentDataDatabaseLink  = "[local]database:/persistent_data"
+    useDatabaseForGroupsData    = false
+    groupsDatabaseLink          = "[local]database:/groups_data"
     localUserGroup(0) = "admin"
     localUserGroup(1) = "moderator"
     localUserGroup(2) = "trusted"

sources/Users/Users_Feature.uc

@@ -3,7 +3,7 @@
  *  database-defined information about group sources. An instance of this
  *  feature is necessary for functioning of Acedia's `UserAPI` methods related
  *  to user groups.
- *      Copyright 2022 Anton Tarasenko
+ *      Copyright 2022-2023 Anton Tarasenko
  *------------------------------------------------------------------------------
  * This file is part of Acedia.
  *
@@ -20,10 +20,19 @@
  * You should have received a copy of the GNU General Public License
  * along with Acedia.  If not, see <https://www.gnu.org/licenses/>.
  */
-class Users_Feature extends Feature;
+class Users_Feature extends Feature
+    dependson(Database);
 
-var private /*config*/ bool             useDatabase;
+/**
-var private /*config*/ string           databaseLink;
+ *  This feature is responsible for managing users: their groups and persistent
+ *  data. Group information can be stored in both configs and databases, while
+ *  persistent data can only be stored in databases.
+ */
+
+var private /*config*/ bool             usePersistentData;
+var private /*config*/ string           persistentDataDatabaseLink;
+var private /*config*/ bool             useDatabaseForGroupsData;
+var private /*config*/ string           groupsDatabaseLink;
 var private /*config*/ array<string>    availableUserGroups;
 
 var private bool diskSaveScheduled;
@@ -39,6 +48,13 @@ struct IDAnnotationPair
     var Text id, annotation;
 };
 
+var private bool        userGroupsDataLoaded;
+var private Database    usersGroupsDatabase;
+var private JSONPointer userGroupsRootPointer;
+var private int         stackedDBReadingRequests;
+
+var private PersistentDataManager currentPersistentDataManager;
+
 //  List of all available user groups for current config
 var private array<Text> loadedUserGroups;
 //  `HashTable` (with group name keys) that stores `HashTable`s used as
@@ -47,6 +63,10 @@ var private HashTable loadedGroupToUsersMap;
 
 var private LoggerAPI.Definition warnNoLocalGroup, warnDuplicateIDs;
 var private LoggerAPI.Definition errCannotCreateLocalGroup;
+var private LoggerAPI.Definition errCannotOpenDatabase, infoUserGroupDataLoaded;
+var private LoggerAPI.Definition errDBBadRootUserGroupData, errDBBadLinkPointer;
+var private LoggerAPI.Definition errDBDamaged, errNoServerCore;
+var private LoggerAPI.Definition errDBContainsNonLowerRegister;
 
 protected function OnEnabled()
 {
@@ -60,6 +80,7 @@ protected function OnEnabled()
         feature.RegisterCommand(class'ACommandUserGroups');
         feature.FreeSelf();
     }
+    LoadUserData();
 }
 
 protected function OnDisabled()
@@ -74,6 +95,9 @@ protected function OnDisabled()
         feature.RemoveCommand(class'ACommandUserGroups');
         feature.FreeSelf();
     }
+    ResetUploadedUserGroups();
+    _.memory.Free(currentPersistentDataManager);
+    currentPersistentDataManager = none;
 }
 
 protected function SwapConfig(FeatureConfig config)
@@ -84,11 +108,195 @@ protected function SwapConfig(FeatureConfig config)
     if (newConfig == none) {
         return;
     }
-    useDatabase         = newConfig.useDatabase;
+    usePersistentData           = newConfig.usePersistentData;
-    databaseLink        = newConfig.databaseLink;
+    persistentDataDatabaseLink  = newConfig.persistentDataDatabaseLink;
-    availableUserGroups = newConfig.localUserGroup;
+    useDatabaseForGroupsData    = newConfig.useDatabaseForGroupsData;
-    class'UserGroup'.static.Initialize();
+    groupsDatabaseLink          = newConfig.groupsDatabaseLink;
-    LoadLocalData();
+    availableUserGroups         = newConfig.localUserGroup;
+    ResetUploadedUserGroups();
+    if (IsEnabled())
+    {
+        if (!_server.IsAvailable())
+        {
+            _.logger.Auto(errNoServerCore);
+            return;
+        }
+        LoadUserData();
+        SetupPersistentData(usePersistentData);
+    }
+}
+
+/**
+ *  Borrows active `PersistentDataManager` (if one is setup for this config).
+ *
+ *  @return Borrowed reference to active `PersistentDataManager`. Can be `none`
+ *      if persistent data isn't setup for the current config.
+ */
+public final function PersistentDataManager BorrowPersistentDataManager()
+{
+    return currentPersistentDataManager;
+}
+
+private final function SetupPersistentData(bool doUsePersistentData)
+{
+    local Text          databaseLinkAsText;
+    local Database      persistentDatabase;
+    local JSONPointer   persistentRootPointer;
+
+    if (!doUsePersistentData)
+    {
+        _.memory.Free(currentPersistentDataManager);
+        currentPersistentDataManager = none;
+        return;
+    }
+    databaseLinkAsText = _.text.FromString(persistentDataDatabaseLink);
+    persistentDatabase = _server.db.Load(databaseLinkAsText);
+    if (persistentDatabase != none) {
+        persistentRootPointer = _server.db.GetPointer(databaseLinkAsText);
+    }
+    else {
+        _.logger.Auto(errCannotOpenDatabase).Arg(databaseLinkAsText);
+    }
+    if (persistentRootPointer != none)
+    {
+        if (currentPersistentDataManager == none)
+        {
+            currentPersistentDataManager = PersistentDataManager(
+                _.memory.Allocate(class'PersistentDataManager'));
+        }
+        currentPersistentDataManager.Setup(
+            persistentDatabase,
+            persistentRootPointer);
+        currentPersistentDataManager.LoadCurrentPlayers();
+    }
+    _.memory.Free(persistentRootPointer);
+    _.memory.Free(persistentDatabase);
+    _.memory.Free(databaseLinkAsText);
+}
+
+private final function LoadUserData()
+{
+    local Text      databaseLinkAsText;
+    local HashTable emptyHashTable;
+
+    if (userGroupsDataLoaded) {
+        return;
+    }
+    if (useDatabaseForGroupsData)
+    {
+        databaseLinkAsText = _.text.FromString(groupsDatabaseLink);
+        usersGroupsDatabase = _server.db.Load(databaseLinkAsText);
+        if (usersGroupsDatabase == none) {
+            _.logger.Auto(errCannotOpenDatabase).Arg(databaseLinkAsText);
+        }
+        else
+        {
+            userGroupsRootPointer = _server.db.GetPointer(databaseLinkAsText);
+            emptyHashTable = _.collections.EmptyHashTable();
+            usersGroupsDatabase.IncrementData(
+                userGroupsRootPointer,
+                emptyHashTable);
+            emptyHashTable.FreeSelf();
+            usersGroupsDatabase.ReadData(userGroupsRootPointer).connect =
+                HandleInitialUserGroupsDataLoading;
+            stackedDBReadingRequests += 1;
+            databaseLinkAsText.FreeSelf();
+        }
+    }
+    else
+    {
+        class'UserGroup'.static.Initialize();
+        LoadLocalData();
+        userGroupsDataLoaded = true;
+    }
+}
+
+private final function HandleInitialUserGroupsDataLoading(
+    Database.DBQueryResult  result,
+    AcediaObject            data,
+    Database                source,
+    int                     requestID)
+{
+    local Text      databaseLinkAsText;
+    local HashTable newGroupData;
+
+    stackedDBReadingRequests -= 1;
+    //  If this counter remains above zero, that means several requests were
+    //  made and this response is to the outdated one
+    if (stackedDBReadingRequests > 0)   return;
+    if (!IsEnabled())                   return;
+
+    newGroupData = HashTable(data);
+    databaseLinkAsText = _.text.FromString(groupsDatabaseLink);
+    if (result == DBR_Success)
+    {
+        if (newGroupData == none)
+        {
+            _.logger.Auto(errDBBadRootUserGroupData).Arg(databaseLinkAsText);
+            return;
+        }
+        userGroupsDataLoaded = true;
+        _.memory.Free(loadedGroupToUsersMap);
+        _.memory.FreeMany(loadedUserGroups);
+        loadedGroupToUsersMap = FilterDBData(newGroupData);
+        loadedUserGroups = loadedGroupToUsersMap.GetTextKeys();
+        newGroupData.FreeSelf();
+        _.logger.Auto(infoUserGroupDataLoaded).Arg(databaseLinkAsText);
+    }
+    else if (result == DBR_InvalidPointer) {
+        _.logger.Auto(errDBBadLinkPointer).Arg(databaseLinkAsText);
+    }
+    else
+    {
+        //  Any other error indicates that database is somehow damaged and
+        //  unusable for our purpose
+        _.logger.Auto(errDBDamaged).Arg(databaseLinkAsText);
+    }
+}
+
+private final function HashTable FilterDBData(HashTable received)
+{
+    local int           i;
+    local array<Text>   allKeys;
+    local AcediaObject  nextItem;
+    local HashTable     result;
+
+    if (received == none) {
+        return none;
+    }
+    result = _.collections.EmptyHashTable();
+    allKeys = received.GetTextKeys();
+    for (i = 0; i < allKeys.length; i += 1)
+    {
+        if (allKeys[i].IsLowerCase())
+        {
+            nextItem = received.GetItem(allKeys[i]);
+            result.SetItem(allKeys[i], nextItem);
+            _.memory.Free(nextItem);
+        }
+        else
+        {
+            allKeys[i].NewRef();
+            _.logger.Auto(errDBContainsNonLowerRegister)
+                .Arg(_.text.FromString(groupsDatabaseLink))
+                .Arg(allKeys[i]);
+        }
+    }
+    _.memory.FreeMany(allKeys);
+    return result;
+}
+
+private final function ResetUploadedUserGroups()
+{
+    _.memory.Free(userGroupsRootPointer);
+    _.memory.Free(usersGroupsDatabase);
+    _.memory.Free(loadedGroupToUsersMap);
+    _.memory.FreeMany(loadedUserGroups);
+    userGroupsRootPointer   = none;
+    usersGroupsDatabase     = none;
+    loadedGroupToUsersMap   = none;
+    loadedUserGroups.length = 0;
+    userGroupsDataLoaded    = false;
 }
 
 private final function LoadLocalData()
@@ -228,7 +436,7 @@ private final function SaveLocalData()
     local Users             currentConfig;
     local HashTableIterator iter;
 
-    if (useDatabase)                    return;
+    if (useDatabaseForGroupsData)       return;
     if (loadedGroupToUsersMap == none)  return;
 
     availableUserGroups.length = 0;
@@ -384,7 +592,8 @@ public final /*unreal*/ function array<string> GetAvailableGroups_S()
  */
 public final function bool AddGroup(BaseText groupName)
 {
-    local Text lowerCaseGroupName;
+    local Text      lowerCaseGroupName;
+    local HashTable emptyHashTable;
 
     if (groupName == none) {
         return false;
@@ -395,8 +604,20 @@ public final function bool AddGroup(BaseText groupName)
         lowerCaseGroupName.FreeSelf();
         return false;
     }
-    //  Try loading local `UserGroup`?
+    if (useDatabaseForGroupsData)
-    if (LoadLocalGroup(lowerCaseGroupName))
+    {
+        emptyHashTable = _.collections.EmptyHashTable();
+        userGroupsRootPointer.Push(lowerCaseGroupName);
+        usersGroupsDatabase.IncrementData(
+            userGroupsRootPointer,
+            emptyHashTable);
+        _.memory.Free(userGroupsRootPointer.Pop());
+        loadedUserGroups[loadedUserGroups.length] = lowerCaseGroupName;
+        loadedGroupToUsersMap.SetItem(lowerCaseGroupName, emptyHashTable);
+        emptyHashTable.FreeSelf();
+        return true;
+    }
+    else if (LoadLocalGroup(lowerCaseGroupName))
     {
         //  Move `lowerCaseGroupName` here, do NOT release the reference
         loadedUserGroups[loadedUserGroups.length] = lowerCaseGroupName;
@@ -478,10 +699,17 @@ public final function bool RemoveGroup(BaseText groupName)
             break;
         }
     }
-    //  Try loading local `UserGroup`?
     loadedGroupToUsersMap.RemoveItem(lowerCaseGroupName);
+    if (useDatabaseForGroupsData)
+    {
+        userGroupsRootPointer.Push(lowerCaseGroupName);
+        usersGroupsDatabase.RemoveData(userGroupsRootPointer);
+        _.memory.Free(userGroupsRootPointer.Pop());
+    }
+    else {
+        ScheduleConfigSave();
+    }
     lowerCaseGroupName.FreeSelf();
-    ScheduleConfigSave();
     return true;
 }
 
@@ -585,20 +813,30 @@ public final function bool AddSteamIDToGroup(
     local Text      lowercaseGroupName;
     local HashTable groupUsers;
 
+    if (steamID == none)                return false;
     if (loadedGroupToUsersMap == none)  return false;
     if (groupName == none)              return false;
 
     lowercaseGroupName = groupName.LowerCopy();
     groupUsers = loadedGroupToUsersMap.GetHashTable(lowercaseGroupName);
-    lowercaseGroupName.FreeSelf();
+    if (groupUsers != none && !groupUsers.HasKey(steamID))
-    //  No specified group? Nothing to add!
+    {
-    if (groupUsers == none) {
+        groupUsers.SetItem(steamID, none);
-        return false;
+        if (useDatabaseForGroupsData)
+        {
+            userGroupsRootPointer.Push(lowerCaseGroupName);
+            userGroupsRootPointer.Push(steamID);
+            usersGroupsDatabase.IncrementData(userGroupsRootPointer, none);
+            _.memory.Free(userGroupsRootPointer.Pop());
+            _.memory.Free(userGroupsRootPointer.Pop());
+        }
+        else {
+            ScheduleConfigSave();
+        }
     }
-    groupUsers.SetItem(steamID, none);
+    lowercaseGroupName.FreeSelf();
-    groupUsers.FreeSelf();
+    _.memory.Free(groupUsers);
-    ScheduleConfigSave();
+    return (groupUsers != none);
-    return true;
 }
 
 /**
@@ -765,19 +1003,30 @@ public final function bool RemoveSteamIDFromGroup(
     local Text      lowercaseGroupName;
     local HashTable groupUsers;
 
+    if (steamID == none)                return false;
     if (groupName == none)              return false;
     if (loadedGroupToUsersMap == none)  return false;
 
     lowercaseGroupName = groupName.LowerCopy();
     groupUsers = loadedGroupToUsersMap.GetHashTable(lowercaseGroupName);
-    lowercaseGroupName.FreeSelf();
+    if (groupUsers != none)
-    if (groupUsers == none) {
+    {
-        return false;
+        hadUser = groupUsers.HasKey(steamID);
+        groupUsers.RemoveItem(steamID);
+        if (useDatabaseForGroupsData)
+        {
+            userGroupsRootPointer.Push(lowerCaseGroupName);
+            userGroupsRootPointer.Push(steamID);
+            usersGroupsDatabase.RemoveData(userGroupsRootPointer);
+            _.memory.Free(userGroupsRootPointer.Pop());
+            _.memory.Free(userGroupsRootPointer.Pop());
+        }
+        else {
+            ScheduleConfigSave();
+        }
     }
-    hadUser = groupUsers.HasKey(steamID);
+    _.memory.Free(groupUsers);
-    groupUsers.RemoveItem(steamID);
+    lowercaseGroupName.FreeSelf();
-    groupUsers.FreeSelf();
-    ScheduleConfigSave();
     return hadUser;
 }
 
@@ -1495,11 +1744,23 @@ public final function SetAnnotationForSteamID(
 
     lowerCaseGroupName = groupName.LowerCopy();
     groupUsers = loadedGroupToUsersMap.GetHashTable(lowerCaseGroupName);
-    lowerCaseGroupName.FreeSelf();
+    if (groupUsers != none && groupUsers.HasKey(steamID))
-    if (groupUsers != none && groupUsers.HasKey(steamID)) {
+    {
         groupUsers.SetItem(steamID, annotation);
+        if (useDatabaseForGroupsData)
+        {
+            userGroupsRootPointer.Push(lowerCaseGroupName);
+            userGroupsRootPointer.Push(steamID);
+            usersGroupsDatabase.WriteData(userGroupsRootPointer, annotation);
+            _.memory.Free(userGroupsRootPointer.Pop());
+            _.memory.Free(userGroupsRootPointer.Pop());
+        }
+        else {
+            ScheduleConfigSave();
+        }
     }
     _.memory.Free(groupUsers);
+    lowerCaseGroupName.FreeSelf();
 }
 
 /**
@@ -1872,13 +2133,13 @@ public final /*unreal*/ function bool IsUserInGroup_S(
  *
  *  Data loaded once is cached and this method returning `true` does not
  *  guarantee that is isn't outdated. Additional, asynchronous queries must be
- *  made to check for that.
+ *  made to check for that. 
  *
  *  @return `true` if user groups' data was loaded and `false` otherwise.
  */
 public final function bool IsUserGroupDataLoaded()
 {
-    return true;
+    return userGroupsDataLoaded;
 }
 
 defaultproperties
@@ -1887,4 +2148,11 @@ defaultproperties
     warnNoLocalGroup = (l=LOG_Warning,m="Expected config to contain `UserGroup` named \"%1\", but it is missing. \"AcediaUsers.ini\" might be misconfigured.")
     warnDuplicateIDs = (l=LOG_Warning,m="Duplicate record for user id \"%1\" is found in `UserGroup` named \"%2\". \"AcediaUsers.ini\" is misconfigured and needs to be fixed.")
     errCannotCreateLocalGroup = (l=LOG_Error,m="Failed to create config section for `UserGroup` named \"%1\".")
+    errCannotOpenDatabase = (l=LOG_Error,m="\"Users_Feature\" has failed to open database given by the link \"%1\".")
+    infoUserGroupDataLoaded = (l=LOG_Info,m="Successfully loaded user data from the database link \"%1\".")
+    errDBBadRootUserGroupData = (l=LOG_Error,m="Database link \"%1\" (configured to load user group data in \"AcediaUsers.ini\") contains incompatible data.")
+    errDBBadLinkPointer = (l=LOG_Error,m="Path inside database link \"%1\" (configured inside \"AcediaUsers.ini\") is invalid.")
+    errDBDamaged = (l=LOG_Error,m="Database given by the link \"%1\" (configured inside \"AcediaUsers.ini\") seems to be damaged.")
+    errNoServerCore = (l=LOG_Error,m="Cannot start \"Users_Feature\", because no `ServerCore` was created.")
+    errDBContainsNonLowerRegister = (l=LOG_Error,m="Database given by the link \"%1\" contains non-lower case key \"%2\". This shouldn't happen, unless someone manually edited database.")
 }