import mysql, {Connection, FieldInfo, MysqlError, Pool, PoolConnection} from 'mysql';
import config from 'config';
import Migration, {MigrationType} from "./Migration";
import {log} from "../Logger";
import {Type} from "../Utils";

export interface QueryResult {
    readonly results: Record<string, unknown>[];
    readonly fields: FieldInfo[];
    readonly other?: Record<string, unknown>;
    foundRows?: number;
}

export async function query(
    queryString: string,
    values?: QueryVariable[],
    connection?: Connection,
): Promise<QueryResult> {
    return await MysqlConnectionManager.query(queryString, values, connection);
}

export default class MysqlConnectionManager {
    private static currentPool?: Pool;
    private static databaseReady: boolean = false;
    private static migrationsRegistered: boolean = false;
    private static readonly migrations: Migration[] = [];

    public static isReady(): boolean {
        return this.databaseReady && this.currentPool !== undefined;
    }

    public static registerMigrations(migrations: MigrationType<Migration>[]): void {
        if (!this.migrationsRegistered) {
            this.migrationsRegistered = true;
            migrations.forEach(m => this.registerMigration(v => new m(v)));
        }
    }

    private static registerMigration(migration: (version: number) => Migration) {
        this.migrations.push(migration(this.migrations.length + 1));
    }

    public static hasMigration(migration: Type<Migration>): boolean {
        for (const m of this.migrations) {
            if (m.constructor === migration) return true;
        }
        return false;
    }

    public static async prepare(runMigrations: boolean = true): Promise<void> {
        if (config.get('mysql.create_database_automatically') === true) {
            const dbName = config.get('mysql.database');
            log.info(`Creating database ${dbName}...`);
            const connection = mysql.createConnection({
                host: config.get('mysql.host'),
                user: config.get('mysql.user'),
                password: config.get('mysql.password'),
                charset: 'utf8mb4',
            });
            await new Promise((resolve, reject) => {
                connection.query(`CREATE DATABASE IF NOT EXISTS ${dbName}`, (error) => {
                    return error !== null ?
                        reject(error) :
                        resolve();
                });
            });
            connection.end();
            log.info(`Database ${dbName} created!`);
        }
        this.databaseReady = true;

        if (runMigrations) await this.handleMigrations();
    }

    public static get pool(): Pool {
        if (this.currentPool === undefined) {
            this.currentPool = this.createPool();
        }
        return this.currentPool;
    }

    private static createPool(): Pool {
        return mysql.createPool({
            connectionLimit: config.get('mysql.connectionLimit'),
            host: config.get('mysql.host'),
            user: config.get('mysql.user'),
            password: config.get('mysql.password'),
            database: config.get('mysql.database'),
            charset: 'utf8mb4',
        });
    }

    public static async endPool(): Promise<void> {
        return await new Promise(resolve => {
            if (this.currentPool === undefined) {
                return resolve();
            }

            this.currentPool.end(() => {
                log.info('Mysql connection pool ended.');
                resolve();
            });
            this.currentPool = undefined;
        });
    }

    public static async query(
        queryString: string,
        values: QueryVariable[] = [],
        connection?: Connection,
    ): Promise<QueryResult> {
        return await new Promise<QueryResult>((resolve, reject) => {
            log.debug('SQL:', log.settings.minLevel === 'trace' || log.settings.minLevel === 'silly' ?
                mysql.format(queryString, values) :
                queryString);

            (connection ? connection : this.pool).query(queryString, values, (error, results, fields) => {
                if (error !== null) {
                    reject(error);
                    return;
                }

                resolve({
                    results: Array.isArray(results) ? results : [],
                    fields: fields !== undefined ? fields : [],
                    other: Array.isArray(results) ? null : results,
                });
            });
        });
    }

    public static async wrapTransaction<T>(transaction: (connection: Connection) => Promise<T>): Promise<T> {
        return await new Promise<T>((resolve, reject) => {
            this.pool.getConnection((err: MysqlError | undefined, connection: PoolConnection) => {
                if (err) {
                    reject(err);
                    return;
                }

                connection.beginTransaction((err?: MysqlError) => {
                    if (err) {
                        reject(err);
                        this.pool.releaseConnection(connection);
                        return;
                    }

                    transaction(connection).then(val => {
                        connection.commit((err?: MysqlError) => {
                            if (err) {
                                this.rejectAndRollback(connection, err, reject);
                                this.pool.releaseConnection(connection);
                                return;
                            }

                            this.pool.releaseConnection(connection);
                            resolve(val);
                        });
                    }).catch(err => {
                        this.rejectAndRollback(connection, err, reject);
                        this.pool.releaseConnection(connection);
                    });
                });
            });
        });
    }

    private static rejectAndRollback(
        connection: Connection,
        err: MysqlError | undefined,
        reject: (err: unknown) => void,
    ) {
        connection.rollback((rollbackErr?: MysqlError) => {
            return rollbackErr ?
                reject(err + '\n' + rollbackErr) :
                reject(err);
        });
    }

    public static async getCurrentMigrationVersion(): Promise<number> {
        let currentVersion = 0;

        try {
            const result = await query('SELECT id FROM migrations ORDER BY id DESC LIMIT 1');
            currentVersion = Number(result.results[0]?.id);
        } catch (e) {
            if (e.code === 'ECONNREFUSED' || e.code !== 'ER_NO_SUCH_TABLE') {
                throw new Error('Cannot run migrations: ' + e.code);
            }
        }

        return currentVersion;
    }

    private static async handleMigrations() {
        const currentVersion = await this.getCurrentMigrationVersion();
        for (const migration of this.migrations) {
            if (await migration.shouldRun(currentVersion)) {
                log.info('Running migration ', migration.version, migration.constructor.name);
                await MysqlConnectionManager.wrapTransaction<void>(async c => {
                    await migration.install(c);
                    await query('INSERT INTO migrations VALUES(?, ?, NOW())', [
                        migration.version,
                        migration.constructor.name,
                    ]);
                });
            }
        }

        for (const migration of this.migrations) {
            migration.registerModels?.();
        }
    }

    /**
     * @param migrationId what migration to rollback. Use with caution. default=0 is for last registered migration.
     */
    public static async rollbackMigration(migrationId: number = 0): Promise<void> {
        migrationId--;
        const migration = this.migrations[migrationId];
        log.info('Rolling back migration ', migration.version, migration.constructor.name);
        await MysqlConnectionManager.wrapTransaction<void>(async c => {
            await migration.rollback(c);
            await query('DELETE FROM migrations WHERE id=?', [migration.version]);
        });
    }

    public static async migrationCommand(args: string[]): Promise<void> {
        try {
            log.info('Current migration:', await this.getCurrentMigrationVersion());

            for (let i = 0; i < args.length; i++) {
                if (args[i] === 'rollback') {
                    let migrationId = 0;
                    if (args.length > i + 1) {
                        migrationId = parseInt(args[i + 1]);
                    }
                    await this.prepare(false);
                    await this.rollbackMigration(migrationId);
                    return;
                }
            }
        } finally {
            await MysqlConnectionManager.endPool();
        }
    }
}

export type QueryVariable =
    | boolean
    | string
    | number
    | Date
    | Buffer
    | null
    | undefined;

export function isQueryVariable(value: unknown): value is QueryVariable {
    return typeof value === 'boolean' ||
        typeof value === "string" ||
        typeof value === 'number' ||
        value instanceof Date ||
        value instanceof Buffer ||
        value === null ||
        value === undefined;
}