/**
 * Database connection utility class
 * Provides centralized connection handling for both main application and worker processes
 */

const debug = require('debug')('agm:db');

class DBConnection {
  constructor(name = 'Database') {
    this.name = name;
    this.connection = null;
    this.isConnected = false;
  }

  /**
   * Connect to MongoDB with comprehensive configuration support
   * @param {Object} options - Connection options
   * @param {boolean} options.debugMode - Enable debug mode for mongoose
   * @param {Function} options.onReady - Callback to execute when DB is ready
   * @param {boolean} options.exitOnError - Whether to exit process on connection error (default: true)
   * @param {boolean} options.setupEventListeners - Whether to set up disconnect/error listeners (default: true)
   * @param {boolean} options.setupExitHandlers - Whether to set up process exit handlers (default: true)
   * @returns {Object} Mongoose connection
   */
  async connect(options = {}) {
    const mongoose = require('mongoose');
    const fs = require('fs-extra');
    const env = require('../env');

    const {
      debugMode = false,
      onReady = null,
      exitOnError = true,
      setupEventListeners = true,
      setupExitHandlers = true
    } = options;

    // Our custom middleware
    mongoose.Promise = global.Promise;

    const ops = {
      connectTimeoutMS: 40000,
      socketTimeoutMS: 30 * 60 * 1000,
      keepAlive: true, 
      keepAliveInitialDelay: 30000,
      autoIndex: !(env.PRODUCTION),
      maxPoolSize: env.DB_MAX_POOLSIZE,
      family: 4,
    }

    // Validate required environment variables
    if (!env.DB_HOSTS) {
      throw new Error('DB_HOSTS environment variable is required');
    }
    if (!env.DB_NAME) {
      throw new Error('DB_NAME environment variable is required');
    }
    if (!env.DB_USR) {
      throw new Error('DB_USR environment variable is required');
    }
    if (!env.DB_PWD) {
      throw new Error('DB_PWD environment variable is required');
    }

    let _uri = `@${env.DB_HOSTS}/${env.DB_NAME}`;
    if (env.DB_HOSTS && !env.DB_HOSTS.includes(',')) {
      ops.directConnection = true;
    }

    if (env.DB_USE_SCALEGRID) {
      // ScaleGrid connection with modern MongoDB driver options
      if (!env.DB_TLS_CA_FILE) {
        throw new Error('DB_TLS_CA_FILE is required when using ScaleGrid');
      }

      try {
        // Don't read the cert file if we're disabling SSL validation
        if (!env.DB_DISABLE_SSL_VALIDATE) {
          const certFileBuf = await fs.readFile(env.DB_TLS_CA_FILE);
        }

        // Modern MongoDB driver configuration for ScaleGrid
        if (env.DB_USE_TLS) {
          // Use TLS but with proper workaround for Node.js v16 bug
          ops.tls = true;
          
          // Complete workaround for Node.js v16 TLS assertion bug
          if (env.DB_DISABLE_SSL_VALIDATE) {
            // Disable all SSL validation to avoid Node.js TLS assertion error
            // tlsInsecure encompasses tlsAllowInvalidCertificates and tlsAllowInvalidHostnames
            ops.tlsInsecure = true;
          } else {
            // Use CA file for proper validation (only if not bypassing)
            ops.tlsCAFile = env.DB_TLS_CA_FILE;
          }
          
          // Additional hostname bypass if needed (only if not using tlsInsecure)
          if (env.DB_DISABLE_HOSTNAME_VERIFY && !env.DB_DISABLE_SSL_VALIDATE) {
            ops.tlsAllowInvalidHostnames = true;
            ops.checkServerIdentity = false;
          }
        }

        // Set replica set in connection options (not deprecated replset)
        if (env.DB_REPLSET) {
          ops.replicaSet = env.DB_REPLSET;
        }

        // Set authentication options for ScaleGrid
        ops.authSource = env.DB_AUTH_SOURCE || 'admin';  // Use env variable, fallback to admin
        ops.authMechanism = 'SCRAM-SHA-256';

      } catch (certError) {
        console.error(`Error loading ScaleGrid CA certificate: ${certError.message}`);
        throw certError;
      }

      // Build ScaleGrid connection string - connect to target database, authenticate via authSource
      _uri = `mongodb://${encodeURIComponent(env.DB_USR)}:${encodeURIComponent(env.DB_PWD)}@${env.DB_HOSTS}/${env.DB_NAME}`;

    } else {
      if (env.DB_REPLSET)
        ops.replicaSet = env.DB_REPLSET

      if (env.DB_USE_TLS) {
        ops.tls = true; ops.sslValidate = true;
        ops.tlsCAFile = env.DB_TLS_CA_FILE;
        ops.tlsCertificateKeyFile = env.DB_TLS_CERT_FILE;
      }

      if (env.DB_USE_X509) {
        ops.authMechanism = 'MONGODB-X509';
        _uri = `mongodb://${encodeURIComponent(env.DB_USR)}` + _uri;
      } else {
        _uri = `mongodb://${env.DB_USR}:${env.DB_PWD}` + _uri;
        ops.authSource = env.DB_AUTH_SOURCE || env.DB_NAME
        ops.authMechanism = 'SCRAM-SHA-1'
      }
    }

    mongoose.set('strictQuery', false);
    mongoose.set('strictPopulate', false);
    mongoose.set('bufferCommands', false); // Disable buffering globally

    // Debug logging before connection
    debug(`Initializing database connection for ${this.name}...`);
    debug(`Connection URI: ${_uri.replace(/\/\/[^:]+:[^@]+@/, '//***:***@')}`);
    debug(`Connection options:`, JSON.stringify(ops, (key, value) => {
      if (key === 'tlsCAFile' || key === 'sslCA') return '[Certificate Path/Data]';
      return value;
    }, 2));

    try {
      // IMPORTANT: Await the connection
      await mongoose.connect(_uri, ops);
      this.connection = mongoose.connection;
      this.isConnected = true;
      
      debug(`✅-> MongoDB connected - ${this.name} ready`);

      // Set up event listeners for connection monitoring
      if (setupEventListeners) {
        this.setupEventListeners(exitOnError);
      }

      // Set up process exit handlers
      if (setupExitHandlers) {
        this.setupExitHandlers();
      }

      if (debugMode) mongoose.set('debug', true);

      // Execute ready callback if provided
      if (onReady && typeof onReady === 'function') {
        await onReady();
      }

    } catch (error) {
      debug(`-> MongoDB connection failed for ${this.name}: ${error.message}`);
      if (exitOnError) {
        process.exit(1);
      } else {
        throw error;
      }
    }

    return this.connection;
  }
  /**
   * Set up connection event listeners
   * @param {boolean} exitOnError - Whether to exit process on connection issues
   */
  setupEventListeners(exitOnError = true) {
    if (!this.connection) {
      debug('Warning: No connection available for event listeners');
      return;
    }

    this.connection.on('disconnected', () => {
      debug(`-> MongoDB lost connection for ${this.name}`);
      this.isConnected = false;
      if (exitOnError) {
        debug('-> Going to exit...');
        process.exit(1);
      }
    });

    this.connection.on('error', (err) => {
      console.error(`MongoDB connection error for ${this.name}:`, err);
      this.isConnected = false;
      if (exitOnError) {
        debug('-> Going to exit...');
        process.exit(1);
      }
    });

    this.connection.on('reconnected', () => {
      debug(`-> MongoDB reconnected for ${this.name}`);
      this.isConnected = true;
    });

    this.connection.on('reconnect', () => { 
      debug(`-> MongoDB reconnect event for ${this.name}`); 
    });
    
    this.connection.on('reconnectFailed', () => { 
      debug(`-> MongoDB gave up reconnecting for ${this.name}`); 
    });
  }

  /**
   * Set up process exit handlers
   */
  setupExitHandlers() {
    const postExit = () => {
      if (this.connection) {
        this.connection.close(() => {
          debug(`Mongoose connection for ${this.name} disconnected through app termination`);
          process.exit(0);
        });
      } else {
        process.exit(0);
      }
    };

    process.on('SIGINT', postExit);
    process.on('SIGTERM', postExit);
  }

  /**
   * Check if database connection is ready for operations
   * @returns {boolean} True if connection is ready
   */
  isReady() {
    return this.connection && this.connection.readyState === 1 && this.isConnected;
  }

  /**
   * Get the mongoose connection object
   * @returns {Object} Mongoose connection
   */
  getConnection() {
    return this.connection;
  }

  /**
   * Close the database connection gracefully
   */
  async close() {
    if (this.connection) {
      await this.connection.close();
      this.isConnected = false;
      debug(`-> ${this.name} database connection closed`);
    }
  }

  /**
   * Simple initialization with sensible defaults
   * @param {Object} options - Configuration options
   * @returns {Object} Mongoose connection
   */
  async initialize(options = {}) {
    const defaults = {
      setupEventListeners: true,
      setupExitHandlers: true, // Can be overridden for workers/special cases
      exitOnError: true
    };
    
    return await this.connect({ ...defaults, ...options });
  }
}

/**
 * Legacy connect function for backward compatibility
 * @param {boolean} debugMode - Enable debug mode for mongoose
 * @returns {Object} Mongoose connection
 */
async function connect(debugMode = false) {
  const dbConnection = new DBConnection('Main Application');
  return await dbConnection.initialize({ debugMode });
}

// Export the class and utility functions
module.exports = connect; // Default export for backward compatibility
module.exports.connect = connect;
module.exports.DBConnection = DBConnection;