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

export interface QueryResult {
    readonly results: any[];
    readonly fields: FieldInfo[];
    readonly other?: any;
    foundRows?: number;
}

export async function query(queryString: string, values?: any, 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 registerMigrations(migrations: Type<Migration>[]) {
        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 async prepare() {
        if (config.get('mysql.create_database_automatically') === true) {
            const dbName = config.get('mysql.database');
            Logger.info(`Creating database ${dbName}...`);
            const connection = mysql.createConnection({
                host: config.get('mysql.host'),
                user: config.get('mysql.user'),
                password: config.get('mysql.password'),
            });
            await new Promise((resolve, reject) => {
                connection.query(`CREATE DATABASE IF NOT EXISTS ${dbName}`, (error) => {
                    if (error !== null) {
                        reject(error);
                    } else {
                        resolve();
                    }
                });
            });
            connection.end();
            Logger.info(`Database ${dbName} created!`);
        }
        this.databaseReady = true;

        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'),
        });
    }

    public static async endPool(): Promise<void> {
        return new Promise(resolve => {
            if (this.currentPool !== undefined) {
                this.currentPool.end(() => {
                    Logger.info('Mysql connection pool ended.');
                    resolve();
                });
                this.currentPool = undefined;
            } else {
                resolve();
            }
        });
    }

    public static async query(queryString: string, values?: any, connection?: Connection): Promise<QueryResult> {
        return await new Promise<QueryResult>((resolve, reject) => {
            Logger.dev('Mysql query:', queryString, '; values:', values);
            (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, connection) => {
                if (err) {
                    reject(err);
                    return;
                }

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

                    transaction(connection).then(val => {
                        connection.commit((err) => {
                            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: any, reject: (err: any) => void) {
        connection.rollback((rollbackErr) => {
            if (rollbackErr) {
                reject(err + '\n' + rollbackErr);
            } else {
                reject(err);
            }
        });
    }

    private static async handleMigrations() {
        let currentVersion = 0;

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

        for (const migration of this.migrations) {
            if (await migration.shouldRun(currentVersion)) {
                Logger.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,
                    ]);
                });
            }
        }
    }
}