const mysql = require("mysql");
const Select = require("./lib/Select");
const Insert = require("./lib/Insert");
const Delete = require("./lib/Delete");
const Update = require("./lib/Update");
const { CreateTable, Structure, AlterTable } = require("./lib/Tables");

/**
 * @typedef {Object} InstanceOptions
 * @property {String} [charset] - Charset to use
 * @property {String} [defaultDatabase] - The default database
 * @property {Boolean} [multipleStatements] - Whether multiple statements should be allowed in a single query
 * @property {Boolean} [insecureAuth] - Whether insecure authentication methods should be allowed
 * @property {String} [customIdentifier] - Sets a custom identifier for this instance
 * @property {Boolean} [isDefault] - Whether this instance is returned by default via 'getInstance'
 */

/**
 * Exported as instance
 */
class awSQL {
    #instances = {};                                                                        // Holds instances. Key is identifier/name.
    #default;                                                                               // Holds the identifier of the default instance (the one used if identifier is omitted)

    /**
     * Creates a new instance (database connection)
     * @param {String} hostname - Hostname where the database is located 
     * @param {String} username - Username to login with
     * @param {String} password
     * @param {InstanceOptions} [options] 
     * @returns {Instance}
     */
    createInstance(hostname="localhost", username, password, options = {
        charset:"utf8mb4",
        defaultDatabase: false,
        multipleStatements: false,
        insecureAuth: false,
        customIdentifier: false,
        isDefault: false,
    }){
        const identifier = options.customIdentifier||`${username}@${hostname}`;             // Set identifier to given identifier or [username]@[hostname]
                                                                                            // If an instance with that identifier exists, throw error
        if (this.#instances[identifier]) throw new Error(`Can't create new instance with identifier "${identifier}": An instance with the same name already exists`);
        const instance = new Instance(hostname, username, password, options.charset, options.defaultDatabase, options.multipleStatements, options.insecureAuth);
        this.#instances[identifier] = instance;                                             // Store instance
        if (options.createAsDefault) this.#default = identifier;                            // If this instance was created with default option set it as the default instance
        return instance;
    }

    /**
     * Returns an instance matching the given identifier
     * 
     * Returns default (or first) instance if no identifier is given
     * @param {String} [identifier] - Identifier of the instance to get 
     * @returns {Instance}
     */
    getInstance(identifier) {
        if (Object.keys(this.#instances).length===0) return undefined;                      // If no instance is found at all return -> Safety return
                                                                                            // If no identifier is set return default or first instance
        if (!identifier) return 
        this.#default?                                                                      
            this.#instances[this.#default]                                                  // If default exists get that
            :
            this.#instances[Object.keys(this.#instances)[0]];                               // Otherwise get instance with that identifier
        return this.#instances[identifier];                                                 // If identifier given return that instance
    }

    /**
     * Returns a list of the identifiers of all instances
     * @returns {Array<String>}
     */
    listInstances(){
        return Object.keys(this.#instances);
    }

    /**
     * Deletes an instance (and closes any open connection)
     * @param {String} identifier - Identifier of the instance to delete
     * @returns {true}
     */
    deleteInstance(identifier){
        if (!identifier) throw new Error("Can't delete Instance: No identifier set");
        if (!this.#instances[identifier]) throw new Error(`Can't delete Instance '${identifier}': No Instance`);
        this.#instances[identifier].destroy();                                              // Memory: Close connection
        if (this.#default === identifier) this.#default = undefined;                        // If this instance was default, clear it from default
        delete this.#instances[identifier];
        return true;
    }
}

/**
 * An awSQL-Instance
 */
class Instance {
    #user;
    #password;
    #host;
    #insecureAuth;
    #multipleStatements;
    #charset;
    #connection;

    #selectedDatabase;
    constructor(hostname="localhost", username, password, charset="utf8mb4", defaultDatabase=false, multipleStatements=false, insecureAuth=false){
        this.#host = hostname;
        this.#user = username;
        this.#password = password;
        this.#charset = charset;
        this.#multipleStatements = multipleStatements;
        this.#insecureAuth = insecureAuth;
        this.#selectedDatabase = defaultDatabase||username;
    }

    /**
     * Connects the instance
     * @returns {undefined}
     */
    connect(){
        return new Promise((resolve, reject) => {
            const connection = mysql.createConnection({                             // Create a new mysql-connection
                user: this.#user,
                password: this.#password,
                host: this.#host,
                insecureAuth: this.#insecureAuth,
                multipleStatements: this.#multipleStatements,
                charset: this.#charset
            });
            this.#connection = connection;                                          // Store the connection
            connection.connect((err) =>{
                if (err) throw err;
                resolve(`Connected to ${this.#host} with user ${this.#user}`);
            });
            connection.on("error", (err) => {
                if (!err.fatal){
                    return;
                }
                this.destroy();                                                     // Memory: Destroy if connection errored
                this.connect();                                                     // And try to reconnect
            })
        })
    }

    /**
     * Destroys the instance
     * @returns {true}
     */
    destroy(){
        if (this.#connection) this.#connection.end();
        this.#connection = undefined;
        return true;
    }

    /**
     * Performs a raw query
     * @param {String} queryString The sql query string to perform.
     * @param {Array<Any>} values - An array holding all replacable ?-values from left to right.
     * @returns {Any} - The individual result of your query 
     */
    queryRaw(queryString, values){
        return new Promise((resolve, reject) => {
            if (!this.#connection) throw new Error("Querying failed: No connection");
            this.#connection.query(queryString, values, (err, result) => {
                if (err) throw err;
                resolve(result);
            })
        })
    }

    /**
     * Returns a list of database names the user has access to
     * @param {Boolean} excludeSchema - Whether to exclude the default database 'information_schema' 
     * @returns {Array<String>}
     */
    async getDatabases (excludeSchema=false){
        let dbs = await this.queryRaw("SHOW DATABASES;");
        if (excludeSchema) dbs = dbs.filter((db)=>db.Database!=="information_schema")
        return dbs.map(db => db.Database);
    }

    /**
     * Selects a default database for future queries
     * @param {String} name - Name of the database
     * @returns {this}
     */
    selectDatabase(name){
        this.#selectedDatabase = name;
        return this;
    }

    /**
     * Returns a list of tables for the selected database
     * - 'multipleStatements' must be active for this to work
     * @param {String} [database] - Database to select. Can be empty as long as a default database was set with 'selectDatabase'
     * @returns {Array}
     */
    async getTables(database){
        if (!this.#multipleStatements) throw new Error("getTables: multipleStatements must be set to 'true' in instance options");
        if (!this.#selectedDatabase && !database) throw new Error("getTables: No database selected");
        const tables = (await this.queryRaw(`USE ${database||this.#selectedDatabase}; SHOW TABLES;`))[1];
        return tables.map(table => table[`Tables_in_${database||this.#selectedDatabase}`]);
    }

    /**
     * Prepares a new select query
     * @param {String} from - Name of the table
     * @param  {...String} [columns] - Name of columns to select. Leave empty to select all
     * @returns {Select}
     */
    select(from, ...columns){
        return new Select(this, this.#selectedDatabase, from, columns);
    }


    /**
     * Prepares a new query to insert data
     * @param {String} into - Name of the table to insert into
     * @returns {Insert}
     */
    insert(into){
        return new Insert(this, this.#selectedDatabase, into);
    }

    /**
     * Prepares a new delete query
     * @param {String} from - Name of the table to delete from 
     * @returns {Delete}
     */
    delete(from){
        return new Delete(this, this.#selectedDatabase, from);
    }

    /**
     * Prepares a new update query
     * @param {String} table - Name of the table to update data in 
     * @returns {Update}
     */
    update(table){
        return new Update(this, this.#selectedDatabase, table);
    }

    /**
     * Drops a whole database
     * - Requires admin privileges
     * @param {String} database - Name of the database to drop
     * @returns {Any}
     */
    async dropDatabase (database){
        return await this.queryRaw(`DROP DATABASE ${database};`);
    }

    /**
     * Drops a whole table
     * @param {String} table - Name of the table to drop
     * @returns {Any}
     */
    async dropTable(table){
        if (!this.#selectedDatabase) throw new Error(`Can't drop table '${table}': Database not set`);
        return await this.queryRaw(`DROP TABLE ${this.#selectedDatabase}.${table}`);
    }

    /**
     * Creates a new database
     * - Requires admin privileges
     * @param {String} name - Name of the database to create
     * @returns {Any}
     */
    async createDatabase(name){
        return await this.queryRaw(`CREATE DATABASE ${name};`);
    }

    /**
     * Prepares to create a new table
     * @param {String} name - Name of the table to create 
     * @returns {CreateTable}
     */
    createTable(name){
        return new CreateTable(this, this.#selectedDatabase, name);
    }

    /**
     * Alters a table and updates to the new given structure.
     * 
     * @param {String} name
     * @returns {AlterTable}
     */
    alterTable(name){
        return new AlterTable(this, this.#selectedDatabase, name);
    }

    /**
     * Prepares to create a new table-structure
     * @returns {Structure}
     */
    createStructure(){
        return new Structure();
    }

    /**
     * Returns the structure object of a table
     * @param {String} table - Name of table to get structure of 
     * @param {String} [database] - Name of the underlying database
     * @returns {Structure}
     */
    async getStructure(table, database){
        if (!this.#selectedDatabase && !database) throw new Error(`Can't get structure of table ${table}: Database not selected`);
        return new Structure(await this.queryRaw(`DESCRIBE ${database||this.#selectedDatabase}.${table};`));
    }

    /**
     * Checks the structure of a table
     * @param {String} table - Name of the table
     * @param {Structure} desiredStructure - Structure to check against
     * @param {String} [database] - Name of the database. If omitted, uses default database 
     * @returns {CheckResult}
     */
    async checkStructure(table, desiredStructure, database){
        if (!this.#selectedDatabase && !database) throw new Error(`Can't get structure of table ${table}: Database not selected`);
        const dbStruc = (await this.getStructure(table, database||this.#selectedDatabase)).get();                           // Get current structure -> Array<Objects>
        const result = {
            errors: [],
            passed: []
        }
        for (let col of desiredStructure){
            const dbCol = dbStruc.find((dbCol) => col.Field === dbCol.Field);                                               // Check if the current table has the field
            if (!dbCol) {
                result.errors.push(`${col.Field}: Missing completely`);
                continue;
            }
            let breakOut = false;
            for (let key in col){
                if (col[key] !== dbCol[key]){                                                                               // If the current key has a different value
                    result.errors.push(`${dbCol.Field}.${key}: Required ${col[key]}, got ${dbCol[key]}`);
                    breakOut=true;
                }
            }
            if (!breakOut){                                                                                                 // If no errors happened
                result.passed.push(`${col.Field}`);
            }
        }
        return result;
    }

    /**
     * Returns total amount of rows of a table
     * @param {String} table - Table name 
     * @returns {Any}
     */
    async total(table){
        return await new Select(this, this.#selectedDatabase, table).count(true).execute();
    }

    /**
     * Returns if connection is established
     * @returns {Boolean}
     */
    isConnected(){
        if (this.#connection) return true;
        return true;
    }
}

/**
 * @typedef {Object} CheckResult
 * @property {Array<String>} errors - String representation of errors found
 * @property {Array<String>} passed - String representation of passed checks
 */

const awSQLInstance = new awSQL();
module.exports = {awSQLInstance, Structure};

/**
 * @exports awSQLInstance
 */