#[cfg(test)]
mod tests;

use serde_json;
use std::collections::HashMap;
use std::error::Error;
use std::path;

extern crate custom_error;
use custom_error::custom_error;

pub mod file;
pub use file::File;

pub mod io;

custom_error! { pub DBError
    InvalidEntityName{entity_name: String} = r#"Cannot use {entity_name} for file or group"#,
    NoGroup{group_name: String} = r#"Group "{group_name}" does not exist"#,
    NoFile{group_name: String, file_name: String} = r#"There is no "{file_name}" file in group\
                                                    "{group_name}""#,
    GroupAlreadyExists{group_name: String} = r#"Group "{group_name}" already exists"#,
    FileAlreadyExists{group_name: String, file_name: String} = r#"File "{file_name}" already exists\
                                                                in the group "{group_name}""#,
}

/// Avarice database is a collection of named JSON values (by default objects),
/// separated into different names groups. Names of such groups and JSON values must only contain
/// numbers and latin letters (ASCII subset).
///
/// This database is only supposed to hold a relatively small amount of data
/// that:
///
/// 1. can be freely and full loaded into memory;
/// 2. then saved all at once.
///
/// Database is loaded and saved on the disk as a directory,
/// that contains subdirectories (with valid names) for each group;
/// those subdirectories in turn must contain "*.json" files (with valid names)
/// that correspond to the stored JSON values.
///
/// Database directory should not contain any other files, but their presence
/// should not prevent database from loading (such files should be ignored).
pub struct Database {
    /// Path to the database's directory
    storage_path: path::PathBuf,
    /// Collection of groups (of JSON values) inside of database
    groups: Vec<Group>,
}

/// Represents a database's group: a ste of named files
pub struct Group {
    /// Name of the group
    name: String,
    /// Maps file names with their contents (as file::File structures)
    files: HashMap<String, File>,
}

impl Database {
    /// Creates new database by loading it from the specified directory.
    /// Directory must contain valid database and be readable.
    pub fn load(storage_path: &path::Path) -> Result<Database, Box<dyn Error>> {
        Ok(Database {
            storage_path: storage_path.to_path_buf(),
            groups: io::read(storage_path)?,
        })
    }

    /// Removes all data from the database.
    pub fn clear(&mut self) {
        self.groups = Vec::new();
    }

    /// Returns path from which this database was loaded (can be changed with `change_path()`).
    pub fn path(&mut self) -> path::PathBuf {
        self.storage_path.clone()
    }

    /// Changes current path of this database. All operations with files will use this path,
    /// unless stated otherwise.
    /// Directory must contain valid database and be readable.
    ///
    /// This method will also remove all data from the current database's path
    /// and fail if it can't.
    pub fn change_path(&mut self, new_path: &path::Path) -> Result<(), Box<dyn Error>> {
        self.write_copy(new_path)?;
        io::clear_dir(&self.storage_path)?;
        self.storage_path = new_path.to_path_buf();
        Ok(())
    }

    /// Erases database's data on disk.
    pub fn erase(self) -> Result<(), Box<dyn Error>> {
        io::clear_dir(&self.storage_path)?;
        Ok(())
    }

    /// Writes copy of the current database into specified directory.
    /// Erases any preexisting database files.
    ///
    /// Empty group won't be saved.
    pub fn write_copy(&self, new_path: &path::Path) -> Result<(), Box<dyn Error>> {
        io::clear_dir(new_path)?;
        io::write(new_path, &self)?;
        Ok(())
    }

    /// Writes current state of the database on the disk.
    ///
    /// Empty group won't be saved.
    pub fn save(&self) -> Result<(), Box<dyn Error>> {
        self.write_copy(&self.storage_path)?;
        Ok(())
    }

    /// Returns names of all the groups in the database.
    pub fn group_names(&self) -> Vec<String> {
        self.groups.iter().map(|x| x.name.clone()).collect()
    }

    /// Returns names of all the files in a particular group.
    pub fn file_names_in(&self, group_name: &str) -> Vec<String> {
        match self.groups.iter().find(|x| x.name.eq(group_name)) {
            Some(group) => group.files.keys().map(|x| x.clone()).collect(),
            None => Vec::new(),
        }
    }

    /// Checks if specified group exists in the database
    pub fn contains_group(&self, group_name: &str) -> bool {
        self.group_index(group_name).is_ok()
    }

    /// Creates a new empty group.
    /// Will produce error if group already exists.
    pub fn create_group(&mut self, group_name: &str) -> Result<(), DBError> {
        assert_name_is_valid(group_name)?;
        self.assert_no_group(group_name)?;
        self.groups.push(Group {
            name: group_name.to_owned(),
            files: HashMap::new(),
        });
        Ok(())
    }

    /// Removes specified group.
    /// Will produce error if group does not exist.
    pub fn remove_group(&mut self, group_name: &str) -> Result<(), DBError> {
        let index = self.group_index(group_name)?;
        self.groups.remove(index);
        Ok(())
    }

    /// Checks if specified file (in a specified group) is contained in the database.
    pub fn contains_file(&self, group_name: &str, file_name: &str) -> bool {
        self.group_files(group_name)
            .and_then(|x| Ok(x.contains_key(&file_name.to_owned())))
            .unwrap_or(false)
    }

    /// Creates new file in the specified group that will contain an empty JSON object.
    /// Will produce error if file already exists.
    pub fn create_file(&mut self, group_name: &str, file_name: &str) -> Result<&mut File, DBError> {
        assert_name_is_valid(&file_name)?;
        let files = self.group_files_mut(group_name)?;
        if files.contains_key(&file_name.to_owned()) {
            return Err(DBError::FileAlreadyExists {
                group_name: group_name.to_owned(),
                file_name: file_name.to_owned(),
            });
        }
        let new_file = File::empty();
        files.insert(file_name.to_owned(), new_file);
        Ok(files
            .get_mut(file_name)
            .expect("Missing value that was just inserted."))
    }

    /// Removes specified file (in a specified group).
    /// Will produce error if file does not exist.
    pub fn remove_file(&mut self, group_name: &str, file_name: &str) -> Result<(), DBError> {
        if self
            .group_files_mut(group_name)?
            .remove(file_name)
            .is_none()
        {
            return Err(DBError::NoFile {
                group_name: group_name.to_owned(),
                file_name: file_name.to_owned(),
            });
        }
        Ok(())
    }

    /// Returns immutable reference to the specified file (in a specified group) as `file::File`.
    /// `None` if file does not exist.
    pub fn file_mut(&mut self, group_name: &str, file_name: &str) -> Option<&mut File> {
        match self.group_files_mut(group_name) {
            Ok(files) => files.get_mut(&file_name.to_owned()),
            _ => None,
        }
    }

    /// Returns mutable reference to the specified file (in a specified group) as `file::File`.
    /// `None` if file does not exist.
    pub fn file(&self, group_name: &str, file_name: &str) -> Option<&File> {
        match self.group_files(group_name) {
            Ok(files) => files.get(&file_name.to_owned()),
            _ => None,
        }
    }

    /// Helper method that raises error if specified group exists.
    fn assert_no_group(&self, group_name: &str) -> Result<(), DBError> {
        if self.group_index(group_name).is_ok() {
            return Err(DBError::GroupAlreadyExists {
                group_name: group_name.to_owned(),
            });
        }
        Ok(())
    }

    /// Returns current index of the specified group in`groups` vector.
    fn group_index(&self, group_name: &str) -> Result<usize, DBError> {
        match self.groups.iter().position(|x| x.name.eq(group_name)) {
            Some(index) => Ok(index),
            _ => {
                return Err(DBError::NoGroup {
                    group_name: group_name.to_owned(),
                })
            }
        }
    }

    //  Helper methods that return (im)mutable reference to `HashMap`
    //  (of 'file_name -> file' map) for a particular group.
    fn group_files_mut(&mut self, group_name: &str) -> Result<&mut HashMap<String, File>, DBError> {
        let group_index = self.group_index(group_name)?;
        Ok(&mut (&mut self.groups[group_index]).files)
    }

    fn group_files(&self, group_name: &str) -> Result<&HashMap<String, File>, DBError> {
        let group_index = self.group_index(group_name)?;
        Ok(&self.groups[group_index].files)
    }
}

/// Name validity check (for groups and files)
fn is_name_valid(entity_name: &str) -> bool {
    entity_name
        .chars()
        .all(|x| x.is_ascii_alphabetic() || x.is_ascii_digit())
}

/// Helper function that raises error if passed name is invalid
fn assert_name_is_valid(entity_name: &str) -> Result<(), DBError> {
    if is_name_valid(entity_name) {
        return Ok(());
    }
    return Err(DBError::InvalidEntityName {
        entity_name: entity_name.to_owned(),
    });
}