/**
 * SMTP Server
 * Core implementation for the refactored SMTP server
 */

import * as plugins from '../../../plugins.js';
import { SmtpState } from './interfaces.js';
import type { ISmtpServerOptions } from './interfaces.js';
import type { ISmtpServer, ISmtpServerConfig, ISessionManager, IConnectionManager, ICommandHandler, IDataHandler, ITlsHandler, ISecurityHandler } from './interfaces.js';
import { SessionManager } from './session-manager.js';
import { ConnectionManager } from './connection-manager.js';
import { CommandHandler } from './command-handler.js';
import { DataHandler } from './data-handler.js';
import { TlsHandler } from './tls-handler.js';
import { SecurityHandler } from './security-handler.js';
import { SMTP_DEFAULTS } from './constants.js';
import { mergeWithDefaults } from './utils/helpers.js';
import { SmtpLogger } from './utils/logging.js';
import { UnifiedEmailServer } from '../../routing/classes.unified.email.server.js';

/**
 * SMTP Server implementation
 * The main server class that coordinates all components
 */
export class SmtpServer implements ISmtpServer {
  /**
   * Email server reference
   */
  private emailServer: UnifiedEmailServer;
  
  /**
   * Session manager
   */
  private sessionManager: ISessionManager;
  
  /**
   * Connection manager
   */
  private connectionManager: IConnectionManager;
  
  /**
   * Command handler
   */
  private commandHandler: ICommandHandler;
  
  /**
   * Data handler
   */
  private dataHandler: IDataHandler;
  
  /**
   * TLS handler
   */
  private tlsHandler: ITlsHandler;
  
  /**
   * Security handler
   */
  private securityHandler: ISecurityHandler;
  
  /**
   * SMTP server options
   */
  private options: ISmtpServerOptions;
  
  /**
   * Net server instance
   */
  private server: plugins.net.Server | null = null;
  
  /**
   * Secure server instance
   */
  private secureServer: plugins.tls.Server | null = null;
  
  /**
   * Whether the server is running
   */
  private running = false;
  
  /**
   * Server recovery state
   */
  private recoveryState = {
    /**
     * Whether recovery is in progress
     */
    recovering: false,
    
    /**
     * Number of consecutive connection failures
     */
    connectionFailures: 0,
    
    /**
     * Last recovery attempt timestamp
     */
    lastRecoveryAttempt: 0,
    
    /**
     * Recovery cooldown in milliseconds
     */
    recoveryCooldown: 5000,
    
    /**
     * Maximum recovery attempts before giving up
     */
    maxRecoveryAttempts: 3,
    
    /**
     * Current recovery attempt
     */
    currentRecoveryAttempt: 0
  };
  
  /**
   * Creates a new SMTP server
   * @param config - Server configuration
   */
  constructor(config: ISmtpServerConfig) {
    this.emailServer = config.emailServer;
    this.options = mergeWithDefaults(config.options);
    
    // Create components or use provided ones
    this.sessionManager = config.sessionManager || new SessionManager({
      socketTimeout: this.options.socketTimeout,
      connectionTimeout: this.options.connectionTimeout,
      cleanupInterval: this.options.cleanupInterval
    });
    
    this.securityHandler = config.securityHandler || new SecurityHandler(
      this.emailServer,
      undefined, // IP reputation service
      this.options.auth
    );
    
    this.tlsHandler = config.tlsHandler || new TlsHandler(
      this.sessionManager,
      {
        key: this.options.key,
        cert: this.options.cert,
        ca: this.options.ca
      }
    );
    
    this.dataHandler = config.dataHandler || new DataHandler(
      this.sessionManager,
      this.emailServer,
      {
        size: this.options.size
      }
    );
    
    this.commandHandler = config.commandHandler || new CommandHandler(
      this.sessionManager,
      {
        hostname: this.options.hostname,
        size: this.options.size,
        maxRecipients: this.options.maxRecipients,
        auth: this.options.auth
      },
      this.dataHandler,
      this.tlsHandler,
      this.securityHandler
    );
    
    this.connectionManager = config.connectionManager || new ConnectionManager(
      this.sessionManager,
      (socket, line) => this.commandHandler.processCommand(socket, line),
      {
        hostname: this.options.hostname,
        maxConnections: this.options.maxConnections,
        socketTimeout: this.options.socketTimeout
      }
    );
  }
  
  /**
   * Start the SMTP server
   * @returns Promise that resolves when server is started
   */
  public async listen(): Promise<void> {
    if (this.running) {
      throw new Error('SMTP server is already running');
    }
    
    try {
      // Create the server
      this.server = plugins.net.createServer((socket) => {
        // Check IP reputation before handling connection
        this.securityHandler.checkIpReputation(socket)
          .then(allowed => {
            if (allowed) {
              this.connectionManager.handleNewConnection(socket);
            } else {
              // Close connection if IP is not allowed
              socket.destroy();
            }
          })
          .catch(error => {
            SmtpLogger.error(`IP reputation check error: ${error instanceof Error ? error.message : String(error)}`, {
              remoteAddress: socket.remoteAddress,
              error: error instanceof Error ? error : new Error(String(error))
            });
            
            // Allow connection on error (fail open)
            this.connectionManager.handleNewConnection(socket);
          });
      });
      
      // Set up error handling with recovery
      this.server.on('error', (err) => {
        SmtpLogger.error(`SMTP server error: ${err.message}`, { error: err });
        
        // Try to recover from specific errors
        if (this.shouldAttemptRecovery(err)) {
          this.attemptServerRecovery('standard', err);
        }
      });
      
      // Start listening
      await new Promise<void>((resolve, reject) => {
        if (!this.server) {
          reject(new Error('Server not initialized'));
          return;
        }
        
        this.server.listen(this.options.port, this.options.host, () => {
          SmtpLogger.info(`SMTP server listening on ${this.options.host || '0.0.0.0'}:${this.options.port}`);
          resolve();
        });
        
        this.server.on('error', reject);
      });
      
      // Start secure server if configured
      if (this.options.securePort && this.tlsHandler.isTlsEnabled()) {
        try {
          // Import the secure server creation utility from our new module
          // This gives us better certificate handling and error resilience
          const { createSecureTlsServer } = await import('./secure-server.js');
          
          // Create secure server with the certificates
          // This uses a more robust approach to certificate loading and validation
          this.secureServer = createSecureTlsServer({
            key: this.options.key,
            cert: this.options.cert,
            ca: this.options.ca
          });
          
          SmtpLogger.info(`Created secure TLS server for port ${this.options.securePort}`);
          
          if (this.secureServer) {
            // Use explicit error handling for secure connections
            this.secureServer.on('tlsClientError', (err, tlsSocket) => {
              SmtpLogger.error(`TLS client error: ${err.message}`, { 
                error: err,
                remoteAddress: tlsSocket.remoteAddress,
                remotePort: tlsSocket.remotePort,
                stack: err.stack
              });
              // No need to destroy, the error event will handle that
            });
            
            // Register the secure connection handler
            this.secureServer.on('secureConnection', (socket) => {
              SmtpLogger.info(`New secure connection from ${socket.remoteAddress}:${socket.remotePort}`, {
                protocol: socket.getProtocol(),
                cipher: socket.getCipher()?.name
              });
              
              // Check IP reputation before handling connection
              this.securityHandler.checkIpReputation(socket)
                .then(allowed => {
                  if (allowed) {
                    // Pass the connection to the connection manager
                    this.connectionManager.handleNewSecureConnection(socket);
                  } else {
                    // Close connection if IP is not allowed
                    socket.destroy();
                  }
                })
                .catch(error => {
                  SmtpLogger.error(`IP reputation check error: ${error instanceof Error ? error.message : String(error)}`, {
                    remoteAddress: socket.remoteAddress,
                    error: error instanceof Error ? error : new Error(String(error)),
                    stack: error instanceof Error ? error.stack : 'No stack trace available'
                  });
                  
                  // Allow connection on error (fail open)
                  this.connectionManager.handleNewSecureConnection(socket);
                });
            });
            
            // Global error handler for the secure server with recovery
            this.secureServer.on('error', (err) => {
              SmtpLogger.error(`SMTP secure server error: ${err.message}`, { 
                error: err,
                stack: err.stack 
              });
              
              // Try to recover from specific errors
              if (this.shouldAttemptRecovery(err)) {
                this.attemptServerRecovery('secure', err);
              }
            });
            
            // Start listening on secure port
            await new Promise<void>((resolve, reject) => {
              if (!this.secureServer) {
                reject(new Error('Secure server not initialized'));
                return;
              }
              
              this.secureServer.listen(this.options.securePort, this.options.host, () => {
                SmtpLogger.info(`SMTP secure server listening on ${this.options.host || '0.0.0.0'}:${this.options.securePort}`);
                resolve();
              });
              
              // Only use error event for startup issues
              this.secureServer.once('error', reject);
            });
          } else {
            SmtpLogger.warn('Failed to create secure server, TLS may not be properly configured');
          }
        } catch (error) {
          SmtpLogger.error(`Error setting up secure server: ${error instanceof Error ? error.message : String(error)}`, {
            error: error instanceof Error ? error : new Error(String(error)),
            stack: error instanceof Error ? error.stack : 'No stack trace available'
          });
        }
      }
      
      this.running = true;
    } catch (error) {
      SmtpLogger.error(`Failed to start SMTP server: ${error instanceof Error ? error.message : String(error)}`, {
        error: error instanceof Error ? error : new Error(String(error))
      });
      
      // Clean up on error
      this.close();
      
      throw error;
    }
  }
  
  /**
   * Stop the SMTP server
   * @returns Promise that resolves when server is stopped
   */
  public async close(): Promise<void> {
    if (!this.running) {
      return;
    }
    
    SmtpLogger.info('Stopping SMTP server');
    
    try {
      // Close all active connections
      this.connectionManager.closeAllConnections();
      
      // Clear all sessions
      this.sessionManager.clearAllSessions();
      
      // Close servers
      const closePromises: Promise<void>[] = [];
      
      if (this.server) {
        closePromises.push(
          new Promise<void>((resolve, reject) => {
            if (!this.server) {
              resolve();
              return;
            }
            
            this.server.close((err) => {
              if (err) {
                reject(err);
              } else {
                resolve();
              }
            });
          })
        );
      }
      
      if (this.secureServer) {
        closePromises.push(
          new Promise<void>((resolve, reject) => {
            if (!this.secureServer) {
              resolve();
              return;
            }
            
            this.secureServer.close((err) => {
              if (err) {
                reject(err);
              } else {
                resolve();
              }
            });
          })
        );
      }
      
      await Promise.all(closePromises);
      
      this.server = null;
      this.secureServer = null;
      this.running = false;
      
      SmtpLogger.info('SMTP server stopped');
    } catch (error) {
      SmtpLogger.error(`Error stopping SMTP server: ${error instanceof Error ? error.message : String(error)}`, {
        error: error instanceof Error ? error : new Error(String(error))
      });
      
      throw error;
    }
  }
  
  /**
   * Get the session manager
   * @returns Session manager instance
   */
  public getSessionManager(): ISessionManager {
    return this.sessionManager;
  }
  
  /**
   * Get the connection manager
   * @returns Connection manager instance
   */
  public getConnectionManager(): IConnectionManager {
    return this.connectionManager;
  }
  
  /**
   * Get the command handler
   * @returns Command handler instance
   */
  public getCommandHandler(): ICommandHandler {
    return this.commandHandler;
  }
  
  /**
   * Get the data handler
   * @returns Data handler instance
   */
  public getDataHandler(): IDataHandler {
    return this.dataHandler;
  }
  
  /**
   * Get the TLS handler
   * @returns TLS handler instance
   */
  public getTlsHandler(): ITlsHandler {
    return this.tlsHandler;
  }
  
  /**
   * Get the security handler
   * @returns Security handler instance
   */
  public getSecurityHandler(): ISecurityHandler {
    return this.securityHandler;
  }
  
  /**
   * Get the server options
   * @returns SMTP server options
   */
  public getOptions(): ISmtpServerOptions {
    return this.options;
  }
  
  /**
   * Get the email server reference
   * @returns Email server instance
   */
  public getEmailServer(): UnifiedEmailServer {
    return this.emailServer;
  }
  
  /**
   * Check if the server is running
   * @returns Whether the server is running
   */
  public isRunning(): boolean {
    return this.running;
  }
  
  /**
   * Check if we should attempt to recover from an error
   * @param error - The error that occurred
   * @returns Whether recovery should be attempted
   */
  private shouldAttemptRecovery(error: Error): boolean {
    // Skip recovery if we're already in recovery mode
    if (this.recoveryState.recovering) {
      return false;
    }
    
    // Check if we've reached the maximum number of recovery attempts
    if (this.recoveryState.currentRecoveryAttempt >= this.recoveryState.maxRecoveryAttempts) {
      SmtpLogger.warn('Maximum recovery attempts reached, not attempting further recovery');
      return false;
    }
    
    // Check if enough time has passed since the last recovery attempt
    const now = Date.now();
    if (now - this.recoveryState.lastRecoveryAttempt < this.recoveryState.recoveryCooldown) {
      SmtpLogger.warn('Recovery cooldown period not elapsed, skipping recovery attempt');
      return false;
    }
    
    // Recoverable errors include:
    // - EADDRINUSE: Address already in use (port conflict)
    // - ECONNRESET: Connection reset by peer
    // - EPIPE: Broken pipe
    // - ETIMEDOUT: Connection timed out
    const recoverableErrors = [
      'EADDRINUSE',
      'ECONNRESET',
      'EPIPE', 
      'ETIMEDOUT',
      'ECONNABORTED',
      'EPROTO',
      'EMFILE' // Too many open files
    ];
    
    // Check if this is a recoverable error
    const errorCode = (error as any).code;
    return recoverableErrors.includes(errorCode);
  }
  
  /**
   * Attempt to recover the server after a critical error
   * @param serverType - The type of server to recover ('standard' or 'secure')
   * @param error - The error that triggered recovery
   */
  private async attemptServerRecovery(serverType: 'standard' | 'secure', error: Error): Promise<void> {
    // Set recovery flag to prevent multiple simultaneous recovery attempts
    if (this.recoveryState.recovering) {
      SmtpLogger.warn('Recovery already in progress, skipping new recovery attempt');
      return;
    }
    
    this.recoveryState.recovering = true;
    this.recoveryState.lastRecoveryAttempt = Date.now();
    this.recoveryState.currentRecoveryAttempt++;
    
    SmtpLogger.info(`Attempting server recovery for ${serverType} server after error: ${error.message}`, {
      attempt: this.recoveryState.currentRecoveryAttempt,
      maxAttempts: this.recoveryState.maxRecoveryAttempts,
      errorCode: (error as any).code
    });
    
    try {
      // Determine which server to restart
      const isStandardServer = serverType === 'standard';
      
      // Close the affected server
      if (isStandardServer && this.server) {
        await new Promise<void>((resolve) => {
          if (!this.server) {
            resolve();
            return;
          }
          
          // First try a clean shutdown
          this.server.close((err) => {
            if (err) {
              SmtpLogger.warn(`Error during server close in recovery: ${err.message}`);
            }
            resolve();
          });
          
          // Set a timeout to force close
          setTimeout(() => {
            resolve();
          }, 3000);
        });
        
        this.server = null;
      } else if (!isStandardServer && this.secureServer) {
        await new Promise<void>((resolve) => {
          if (!this.secureServer) {
            resolve();
            return;
          }
          
          // First try a clean shutdown
          this.secureServer.close((err) => {
            if (err) {
              SmtpLogger.warn(`Error during secure server close in recovery: ${err.message}`);
            }
            resolve();
          });
          
          // Set a timeout to force close
          setTimeout(() => {
            resolve();
          }, 3000);
        });
        
        this.secureServer = null;
      }
      
      // Short delay before restarting
      await new Promise<void>((resolve) => setTimeout(resolve, 1000));
      
      // Clean up any lingering connections
      this.connectionManager.closeAllConnections();
      this.sessionManager.clearAllSessions();
      
      // Restart the affected server
      if (isStandardServer) {
        // Create and start the standard server
        this.server = plugins.net.createServer((socket) => {
          // Check IP reputation before handling connection
          this.securityHandler.checkIpReputation(socket)
            .then(allowed => {
              if (allowed) {
                this.connectionManager.handleNewConnection(socket);
              } else {
                // Close connection if IP is not allowed
                socket.destroy();
              }
            })
            .catch(error => {
              SmtpLogger.error(`IP reputation check error: ${error instanceof Error ? error.message : String(error)}`, {
                remoteAddress: socket.remoteAddress,
                error: error instanceof Error ? error : new Error(String(error))
              });
              
              // Allow connection on error (fail open)
              this.connectionManager.handleNewConnection(socket);
            });
        });
        
        // Set up error handling with recovery
        this.server.on('error', (err) => {
          SmtpLogger.error(`SMTP server error after recovery: ${err.message}`, { error: err });
          
          // Try to recover again if needed
          if (this.shouldAttemptRecovery(err)) {
            this.attemptServerRecovery('standard', err);
          }
        });
        
        // Start listening again
        await new Promise<void>((resolve, reject) => {
          if (!this.server) {
            reject(new Error('Server not initialized during recovery'));
            return;
          }
          
          this.server.listen(this.options.port, this.options.host, () => {
            SmtpLogger.info(`SMTP server recovered and listening on ${this.options.host || '0.0.0.0'}:${this.options.port}`);
            resolve();
          });
          
          // Only use error event for startup issues during recovery
          this.server.once('error', (err) => {
            SmtpLogger.error(`Failed to restart server during recovery: ${err.message}`);
            reject(err);
          });
        });
      } else if (this.options.securePort && this.tlsHandler.isTlsEnabled()) {
        // Try to recreate the secure server
        try {
          // Import the secure server creation utility
          const { createSecureTlsServer } = await import('./secure-server.js');
          
          // Create secure server with the certificates
          this.secureServer = createSecureTlsServer({
            key: this.options.key,
            cert: this.options.cert,
            ca: this.options.ca
          });
          
          if (this.secureServer) {
            SmtpLogger.info(`Created secure TLS server for port ${this.options.securePort} during recovery`);
            
            // Use explicit error handling for secure connections
            this.secureServer.on('tlsClientError', (err, tlsSocket) => {
              SmtpLogger.error(`TLS client error after recovery: ${err.message}`, { 
                error: err,
                remoteAddress: tlsSocket.remoteAddress,
                remotePort: tlsSocket.remotePort,
                stack: err.stack
              });
            });
            
            // Register the secure connection handler
            this.secureServer.on('secureConnection', (socket) => {
              // Check IP reputation before handling connection
              this.securityHandler.checkIpReputation(socket)
                .then(allowed => {
                  if (allowed) {
                    // Pass the connection to the connection manager
                    this.connectionManager.handleNewSecureConnection(socket);
                  } else {
                    // Close connection if IP is not allowed
                    socket.destroy();
                  }
                })
                .catch(error => {
                  SmtpLogger.error(`IP reputation check error after recovery: ${error instanceof Error ? error.message : String(error)}`, {
                    remoteAddress: socket.remoteAddress,
                    error: error instanceof Error ? error : new Error(String(error))
                  });
                  
                  // Allow connection on error (fail open)
                  this.connectionManager.handleNewSecureConnection(socket);
                });
            });
            
            // Global error handler for the secure server with recovery
            this.secureServer.on('error', (err) => {
              SmtpLogger.error(`SMTP secure server error after recovery: ${err.message}`, { 
                error: err,
                stack: err.stack 
              });
              
              // Try to recover again if needed
              if (this.shouldAttemptRecovery(err)) {
                this.attemptServerRecovery('secure', err);
              }
            });
            
            // Start listening on secure port again
            await new Promise<void>((resolve, reject) => {
              if (!this.secureServer) {
                reject(new Error('Secure server not initialized during recovery'));
                return;
              }
              
              this.secureServer.listen(this.options.securePort, this.options.host, () => {
                SmtpLogger.info(`SMTP secure server recovered and listening on ${this.options.host || '0.0.0.0'}:${this.options.securePort}`);
                resolve();
              });
              
              // Only use error event for startup issues during recovery
              this.secureServer.once('error', (err) => {
                SmtpLogger.error(`Failed to restart secure server during recovery: ${err.message}`);
                reject(err);
              });
            });
          } else {
            SmtpLogger.warn('Failed to create secure server during recovery');
          }
        } catch (error) {
          SmtpLogger.error(`Error setting up secure server during recovery: ${error instanceof Error ? error.message : String(error)}`);
        }
      }
      
      // Recovery successful
      SmtpLogger.info('Server recovery completed successfully');
      
    } catch (recoveryError) {
      SmtpLogger.error(`Server recovery failed: ${recoveryError instanceof Error ? recoveryError.message : String(recoveryError)}`, {
        error: recoveryError instanceof Error ? recoveryError : new Error(String(recoveryError)),
        attempt: this.recoveryState.currentRecoveryAttempt,
        maxAttempts: this.recoveryState.maxRecoveryAttempts
      });
    } finally {
      // Reset recovery flag
      this.recoveryState.recovering = false;
    }
  }
}