// =====================================================
// 資料庫連接配置
// =====================================================

import mysql from 'mysql2/promise';

// 資料庫配置
const dbConfig = {
  host: process.env.DB_HOST || 'mysql.theaken.com',
  port: parseInt(process.env.DB_PORT || '33306'),
  user: process.env.DB_USER || 'AI_Platform',
  password: process.env.DB_PASSWORD || 'Aa123456',
  database: process.env.DB_NAME || 'db_AI_Platform',
  charset: 'utf8mb4',
  timezone: '+08:00',
  acquireTimeout: 60000,
  timeout: 60000,
  reconnect: true,
  connectionLimit: 10,
  queueLimit: 0,
  // 添加連接重試和錯誤處理配置
  retryDelay: 2000,
  maxRetries: 3,
  // 添加連接池配置
  idleTimeout: 300000,
  maxIdle: 10,
  // 添加 SSL 配置（如果需要）
  ssl: false,
};

// 創建連接池
const pool = mysql.createPool(dbConfig);

// 資料庫連接類
export class Database {
  private static instance: Database;
  private pool: mysql.Pool;

  private constructor() {
    this.pool = pool;
  }

  public static getInstance(): Database {
    if (!Database.instance) {
      Database.instance = new Database();
    }
    return Database.instance;
  }

  // 獲取連接
  public async getConnection(): Promise<mysql.PoolConnection> {
    return await this.pool.getConnection();
  }

  // 執行查詢
  public async query<T = any>(sql: string, params?: any[]): Promise<T[]> {
    let connection;
    let retries = 0;
    const maxRetries = 3;

    while (retries < maxRetries) {
      try {
        connection = await this.getConnection();
        const [rows] = await connection.execute(sql, params);
        return rows as T[];
      } catch (error: any) {
        console.error(`資料庫查詢錯誤 (嘗試 ${retries + 1}/${maxRetries}):`, error.message);
        
        if (connection) {
          connection.release();
        }
        
        if (error.code === 'ECONNRESET' || error.code === 'PROTOCOL_CONNECTION_LOST') {
          retries++;
          if (retries < maxRetries) {
            console.log(`等待 ${2000 * retries}ms 後重試...`);
            await new Promise(resolve => setTimeout(resolve, 2000 * retries));
            continue;
          }
        }
        
        throw error;
      } finally {
        if (connection) {
          connection.release();
        }
      }
    }
    
    throw new Error('資料庫連接失敗，已達到最大重試次數');
  }

  // 執行單一查詢
  public async queryOne<T = any>(sql: string, params?: any[]): Promise<T | null> {
    try {
      const results = await this.query<T>(sql, params);
      return results.length > 0 ? results[0] : null;
    } catch (error) {
      console.error('資料庫單一查詢錯誤:', error);
      throw error;
    }
  }

  // 執行插入
  public async insert(sql: string, params?: any[]): Promise<mysql.ResultSetHeader> {
    const connection = await this.getConnection();
    try {
      const [result] = await connection.execute(sql, params);
      return result as mysql.ResultSetHeader;
    } finally {
      connection.release();
    }
  }

  // 執行更新
  public async update(sql: string, params?: any[]): Promise<mysql.ResultSetHeader> {
    const connection = await this.getConnection();
    try {
      const [result] = await connection.execute(sql, params);
      return result as mysql.ResultSetHeader;
    } finally {
      connection.release();
    }
  }

  // 執行刪除
  public async delete(sql: string, params?: any[]): Promise<mysql.ResultSetHeader> {
    const connection = await this.getConnection();
    try {
      const [result] = await connection.execute(sql, params);
      return result as mysql.ResultSetHeader;
    } finally {
      connection.release();
    }
  }

  // 開始事務
  public async beginTransaction(): Promise<mysql.PoolConnection> {
    const connection = await this.getConnection();
    await connection.beginTransaction();
    return connection;
  }

  // 提交事務
  public async commit(connection: mysql.PoolConnection): Promise<void> {
    await connection.commit();
    connection.release();
  }

  // 回滾事務
  public async rollback(connection: mysql.PoolConnection): Promise<void> {
    await connection.rollback();
    connection.release();
  }

  // 關閉連接池
  public async close(): Promise<void> {
    await this.pool.end();
  }
}

// 導出單例實例
export const db = Database.getInstance();

// 導出類型
export type { PoolConnection } from 'mysql2/promise';