/**
 * SMTP Client Connection Manager
 * Connection pooling and lifecycle management
 */

import * as net from 'node:net';
import * as tls from 'node:tls';
import { EventEmitter } from 'node:events';
import { DEFAULTS, CONNECTION_STATES } from './constants.js';
import type { 
  ISmtpClientOptions, 
  ISmtpConnection, 
  IConnectionPoolStatus,
  ConnectionState 
} from './interfaces.js';
import { logConnection, logDebug } from './utils/logging.js';
import { generateConnectionId } from './utils/helpers.js';

export class ConnectionManager extends EventEmitter {
  private options: ISmtpClientOptions;
  private connections: Map<string, ISmtpConnection> = new Map();
  private pendingConnections: Set<string> = new Set();
  private idleTimeout: NodeJS.Timeout | null = null;
  
  constructor(options: ISmtpClientOptions) {
    super();
    this.options = options;
    this.setupIdleCleanup();
  }
  
  /**
   * Get or create a connection
   */
  public async getConnection(): Promise<ISmtpConnection> {
    // Try to reuse an idle connection if pooling is enabled
    if (this.options.pool) {
      const idleConnection = this.findIdleConnection();
      if (idleConnection) {
        const connectionId = this.getConnectionId(idleConnection) || 'unknown';
        logDebug('Reusing idle connection', this.options, { connectionId });
        return idleConnection;
      }
      
      // Check if we can create a new connection
      if (this.getActiveConnectionCount() >= (this.options.maxConnections || DEFAULTS.MAX_CONNECTIONS)) {
        throw new Error('Maximum number of connections reached');
      }
    }
    
    return this.createConnection();
  }
  
  /**
   * Create a new connection
   */
  public async createConnection(): Promise<ISmtpConnection> {
    const connectionId = generateConnectionId();
    
    try {
      this.pendingConnections.add(connectionId);
      logConnection('connecting', this.options, { connectionId });
      
      const socket = await this.establishSocket();
      const connection: ISmtpConnection = {
        socket,
        state: CONNECTION_STATES.CONNECTED as ConnectionState,
        options: this.options,
        secure: this.options.secure || false,
        createdAt: new Date(),
        lastActivity: new Date(),
        messageCount: 0
      };
      
      this.setupSocketHandlers(socket, connectionId);
      this.connections.set(connectionId, connection);
      this.pendingConnections.delete(connectionId);
      
      logConnection('connected', this.options, { connectionId });
      this.emit('connection', connection);
      
      return connection;
    } catch (error) {
      this.pendingConnections.delete(connectionId);
      logConnection('error', this.options, { connectionId, error });
      throw error;
    }
  }
  
  /**
   * Release a connection back to the pool or close it
   */
  public releaseConnection(connection: ISmtpConnection): void {
    const connectionId = this.getConnectionId(connection);
    
    if (!connectionId || !this.connections.has(connectionId)) {
      return;
    }
    
    if (this.options.pool && this.shouldReuseConnection(connection)) {
      // Return to pool
      connection.state = CONNECTION_STATES.READY as ConnectionState;
      connection.lastActivity = new Date();
      logDebug('Connection returned to pool', this.options, { connectionId });
    } else {
      // Close connection
      this.closeConnection(connection);
    }
  }
  
  /**
   * Close a specific connection
   */
  public closeConnection(connection: ISmtpConnection): void {
    const connectionId = this.getConnectionId(connection);
    
    if (connectionId) {
      this.connections.delete(connectionId);
    }
    
    connection.state = CONNECTION_STATES.CLOSING as ConnectionState;
    
    try {
      if (!connection.socket.destroyed) {
        connection.socket.destroy();
      }
    } catch (error) {
      logDebug('Error closing connection', this.options, { error });
    }
    
    logConnection('disconnected', this.options, { connectionId });
    this.emit('disconnect', connection);
  }
  
  /**
   * Close all connections
   */
  public closeAllConnections(): void {
    logDebug('Closing all connections', this.options);
    
    for (const connection of this.connections.values()) {
      this.closeConnection(connection);
    }
    
    this.connections.clear();
    this.pendingConnections.clear();
    
    if (this.idleTimeout) {
      clearInterval(this.idleTimeout);
      this.idleTimeout = null;
    }
  }
  
  /**
   * Get connection pool status
   */
  public getPoolStatus(): IConnectionPoolStatus {
    const total = this.connections.size;
    const active = Array.from(this.connections.values())
      .filter(conn => conn.state === CONNECTION_STATES.BUSY).length;
    const idle = total - active;
    const pending = this.pendingConnections.size;
    
    return { total, active, idle, pending };
  }
  
  /**
   * Update connection activity timestamp
   */
  public updateActivity(connection: ISmtpConnection): void {
    connection.lastActivity = new Date();
  }
  
  private async establishSocket(): Promise<net.Socket | tls.TLSSocket> {
    return new Promise((resolve, reject) => {
      const timeout = this.options.connectionTimeout || DEFAULTS.CONNECTION_TIMEOUT;
      let socket: net.Socket | tls.TLSSocket;
      
      if (this.options.secure) {
        // Direct TLS connection
        socket = tls.connect({
          host: this.options.host,
          port: this.options.port,
          ...this.options.tls
        });
      } else {
        // Plain connection
        socket = new net.Socket();
        socket.connect(this.options.port, this.options.host);
      }
      
      const timeoutHandler = setTimeout(() => {
        socket.destroy();
        reject(new Error(`Connection timeout after ${timeout}ms`));
      }, timeout);
      
      socket.once('connect', () => {
        clearTimeout(timeoutHandler);
        resolve(socket);
      });
      
      socket.once('error', (error) => {
        clearTimeout(timeoutHandler);
        reject(error);
      });
    });
  }
  
  private setupSocketHandlers(socket: net.Socket | tls.TLSSocket, connectionId: string): void {
    const socketTimeout = this.options.socketTimeout || DEFAULTS.SOCKET_TIMEOUT;
    
    socket.setTimeout(socketTimeout);
    
    socket.on('timeout', () => {
      logDebug('Socket timeout', this.options, { connectionId });
      socket.destroy();
    });
    
    socket.on('error', (error) => {
      logConnection('error', this.options, { connectionId, error });
      this.connections.delete(connectionId);
    });
    
    socket.on('close', () => {
      this.connections.delete(connectionId);
      logDebug('Socket closed', this.options, { connectionId });
    });
  }
  
  private findIdleConnection(): ISmtpConnection | null {
    for (const connection of this.connections.values()) {
      if (connection.state === CONNECTION_STATES.READY) {
        return connection;
      }
    }
    return null;
  }
  
  private shouldReuseConnection(connection: ISmtpConnection): boolean {
    const maxMessages = this.options.maxMessages || DEFAULTS.MAX_MESSAGES;
    const maxAge = 300000; // 5 minutes
    const age = Date.now() - connection.createdAt.getTime();
    
    return connection.messageCount < maxMessages && 
           age < maxAge && 
           !connection.socket.destroyed;
  }
  
  private getActiveConnectionCount(): number {
    return this.connections.size + this.pendingConnections.size;
  }
  
  private getConnectionId(connection: ISmtpConnection): string | null {
    for (const [id, conn] of this.connections.entries()) {
      if (conn === connection) {
        return id;
      }
    }
    return null;
  }
  
  private setupIdleCleanup(): void {
    if (!this.options.pool) {
      return;
    }
    
    const cleanupInterval = DEFAULTS.POOL_IDLE_TIMEOUT;
    
    this.idleTimeout = setInterval(() => {
      const now = Date.now();
      const connectionsToClose: ISmtpConnection[] = [];
      
      for (const connection of this.connections.values()) {
        const idleTime = now - connection.lastActivity.getTime();
        
        if (connection.state === CONNECTION_STATES.READY && idleTime > cleanupInterval) {
          connectionsToClose.push(connection);
        }
      }
      
      for (const connection of connectionsToClose) {
        logDebug('Closing idle connection', this.options);
        this.closeConnection(connection);
      }
    }, cleanupInterval);
  }
}