// =====================================================
// 終極連線殺手 - 強制清理所有連線
// =====================================================

import mysql from 'mysql2/promise';

export class UltimateConnectionKiller {
  private static instance: UltimateConnectionKiller;

  private constructor() {}

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

  // 終極清理 - 殺死所有連線
  public async ultimateKill() {
    console.log('💀 執行終極連線清理...');
    
    try {
      // 1. 建立一個臨時連線來執行清理
      const tempConnection = await mysql.createConnection({
        host: process.env.DB_HOST || '122.100.99.161',
        port: parseInt(process.env.DB_PORT || '43306'),
        user: process.env.DB_USER || 'A999',
        password: process.env.DB_PASSWORD || '1023',
        database: process.env.DB_NAME || 'db_AI_Platform',
        charset: 'utf8mb4',
        timezone: '+08:00',
      });

      try {
        // 2. 獲取所有連線
        const [connections] = await tempConnection.execute(`
          SELECT ID, USER, HOST, DB, COMMAND, TIME, STATE, INFO
          FROM information_schema.PROCESSLIST 
          WHERE USER = ?
          ORDER BY TIME DESC
        `, [process.env.DB_USER || 'A999']);

        console.log(`🔍 找到 ${connections.length} 個連線需要清理`);

        // 3. 殺死所有連線（除了當前連線）
        let killedCount = 0;
        for (const conn of connections) {
          if (conn.ID !== tempConnection.threadId) {
            try {
              await tempConnection.execute(`KILL ${conn.ID}`);
              console.log(`💀 已殺死連線 ${conn.ID} (用戶: ${conn.USER}, 時間: ${conn.TIME}s)`);
              killedCount++;
            } catch (error: any) {
              console.log(`⚠️ 無法殺死連線 ${conn.ID}: ${error.message}`);
            }
          }
        }

        console.log(`✅ 已殺死 ${killedCount} 個連線`);

        // 4. 等待連線完全關閉
        console.log('⏳ 等待連線完全關閉...');
        await new Promise(resolve => setTimeout(resolve, 3000));

        // 5. 再次檢查狀態
        const [finalConnections] = await tempConnection.execute(`
          SELECT COUNT(*) as count FROM information_schema.PROCESSLIST 
          WHERE USER = ?
        `, [process.env.DB_USER || 'A999']);

        const remainingConnections = finalConnections[0].count;
        console.log(`📊 清理後剩餘連線: ${remainingConnections}`);

        if (remainingConnections <= 1) {
          console.log('🎉 連線清理成功！');
        } else {
          console.warn(`⚠️ 仍有 ${remainingConnections - 1} 個連線未清理`);
        }

        return {
          success: true,
          killedCount,
          remainingConnections: remainingConnections - 1, // 減去當前連線
          message: `已殺死 ${killedCount} 個連線，剩餘 ${remainingConnections - 1} 個`
        };

      } finally {
        // 6. 關閉臨時連線
        await tempConnection.end();
        console.log('🔌 臨時連線已關閉');
      }

    } catch (error) {
      console.error('❌ 終極清理失敗:', error);
      return {
        success: false,
        error: error instanceof Error ? error.message : '未知錯誤'
      };
    }
  }

  // 檢查連線狀態
  public async checkStatus() {
    try {
      const tempConnection = await mysql.createConnection({
        host: process.env.DB_HOST || '122.100.99.161',
        port: parseInt(process.env.DB_PORT || '43306'),
        user: process.env.DB_USER || 'A999',
        password: process.env.DB_PASSWORD || '1023',
        database: process.env.DB_NAME || 'db_AI_Platform',
        charset: 'utf8mb4',
        timezone: '+08:00',
      });

      try {
        // 獲取連線統計
        const [statusResult] = await tempConnection.execute(`
          SHOW STATUS LIKE 'Threads_connected'
        `);
        
        const [maxConnResult] = await tempConnection.execute(`
          SHOW VARIABLES LIKE 'max_connections'
        `);

        const [connections] = await tempConnection.execute(`
          SELECT ID, USER, HOST, DB, COMMAND, TIME, STATE, INFO
          FROM information_schema.PROCESSLIST 
          WHERE USER = ?
          ORDER BY TIME DESC
        `, [process.env.DB_USER || 'A999']);

        const currentConnections = statusResult[0]?.Value || 0;
        const maxConnections = maxConnResult[0]?.Value || 100;
        const usagePercentage = (currentConnections / maxConnections) * 100;

        return {
          currentConnections: parseInt(currentConnections),
          maxConnections: parseInt(maxConnections),
          usagePercentage,
          connectionDetails: connections,
          connectionCount: connections.length
        };

      } finally {
        await tempConnection.end();
      }

    } catch (error) {
      console.error('❌ 檢查狀態失敗:', error);
      return null;
    }
  }

  // 強制重啟資料庫連線
  public async forceRestart() {
    console.log('🔄 強制重啟資料庫連線...');
    
    try {
      // 1. 先殺死所有連線
      await this.ultimateKill();
      
      // 2. 等待一段時間
      console.log('⏳ 等待系統穩定...');
      await new Promise(resolve => setTimeout(resolve, 5000));
      
      // 3. 檢查狀態
      const status = await this.checkStatus();
      
      if (status && status.connectionCount <= 1) {
        console.log('✅ 資料庫連線重啟成功');
        return { success: true, message: '資料庫連線重啟成功' };
      } else {
        console.warn('⚠️ 資料庫連線重啟後仍有連線存在');
        return { success: false, message: '重啟後仍有連線存在' };
      }

    } catch (error) {
      console.error('❌ 強制重啟失敗:', error);
      return { success: false, error: error instanceof Error ? error.message : '未知錯誤' };
    }
  }
}

// 導出單例實例
export const ultimateKiller = UltimateConnectionKiller.getInstance();