import { EventEmitter } from 'events';
import { createHash, randomBytes } from 'crypto';

/**
 * Ultra-Enhanced Error Handling Manager for ZAI Platform
 * Advanced error recovery, circuit breakers, and intelligent fault tolerance
 */
export class ErrorHandlingManager extends EventEmitter {
  constructor() {
    super();
    
    this.errorPatterns = new Map();
    this.circuitBreakers = new Map();
    this.recoveryStrategies = new Map();
    this.errorMetrics = new Map();
    this.faultTolerance = new Map();
    
    // Error handling configuration
    this.errorConfig = {
      maxRetries: 3,
      retryDelay: 1000, // milliseconds
      circuitBreakerThreshold: 5,
      circuitBreakerTimeout: 30000, // 30 seconds
      errorAggregationWindow: 60000, // 1 minute
      criticalErrorThreshold: 0.1, // 10%
      autoRecoveryEnabled: true,
      intelligentRetryEnabled: true
    };
    
    // Error classification system
    this.errorClassification = {
      TRANSIENT: {
        retryable: true,
        maxRetries: 5,
        backoffStrategy: 'exponential',
        examples: ['network_timeout', 'temporary_unavailable', 'rate_limit']
      },
      PERMANENT: {
        retryable: false,
        maxRetries: 0,
        backoffStrategy: 'none',
        examples: ['authentication_failed', 'invalid_input', 'not_found']
      },
      INTERMITTENT: {
        retryable: true,
        maxRetries: 3,
        backoffStrategy: 'linear',
        examples: ['database_connection', 'service_degraded', 'partial_failure']
      },
      CRITICAL: {
        retryable: true,
        maxRetries: 1,
        backoffStrategy: 'immediate',
        examples: ['security_breach', 'data_corruption', 'system_failure']
      }
    };
    
    // Recovery strategies
    this.recoveryStrategies = new Map([
      ['service_restart', this.restartService.bind(this)],
      ['fallback_service', this.activateFallbackService.bind(this)],
      ['circuit_breaker', this.activateCircuitBreaker.bind(this)],
      ['graceful_degradation', this.enableGracefulDegradation.bind(this)],
      ['emergency_shutdown', this.emergencyShutdown.bind(this)],
      ['data_recovery', this.initiateDataRecovery.bind(this)],
      ['load_balancing', this.redistributeLoad.bind(this)],
      ['cache_invalidation', this.invalidateCache.bind(this)]
    ]);
    
    this.initializeErrorHandling();
    this.startErrorMonitoring();
    
    console.log('🛡️ Ultra-Enhanced Error Handling Manager initialized');
  }

  /**
   * Initialize error handling systems
   */
  initializeErrorHandling() {
    // Initialize circuit breakers for critical services
    const criticalServices = [
      'license-service',
      'payment-service',
      'user-service',
      'analytics-service',
      'security-service',
      'blockchain-service',
      'edge-computing-service'
    ];
    
    for (const service of criticalServices) {
      this.circuitBreakers.set(service, {
        state: 'CLOSED', // CLOSED, OPEN, HALF_OPEN
        failureCount: 0,
        lastFailureTime: null,
        successCount: 0,
        threshold: this.errorConfig.circuitBreakerThreshold,
        timeout: this.errorConfig.circuitBreakerTimeout,
        halfOpenMaxCalls: 3
      });
    }
    
    // Initialize error metrics tracking
    this.errorMetrics.set('global', {
      totalErrors: 0,
      errorRate: 0,
      criticalErrors: 0,
      recoveredErrors: 0,
      unrecoveredErrors: 0,
      averageRecoveryTime: 0,
      errorsByType: new Map(),
      errorsByService: new Map()
    });
    
    console.log('🛡️ Error handling systems initialized');
  }

  /**
   * Enhanced error handling with intelligent recovery
   */
  async handleError(error, context = {}) {
    const errorId = this.generateErrorId();
    const timestamp = Date.now();
    
    const errorInfo = {
      id: errorId,
      timestamp,
      error: {
        message: error.message,
        stack: error.stack,
        name: error.name,
        code: error.code
      },
      context: {
        service: context.service || 'unknown',
        operation: context.operation || 'unknown',
        userId: context.userId,
        requestId: context.requestId,
        ...context
      },
      classification: null,
      recoveryStrategy: null,
      recoveryAttempts: 0,
      recovered: false,
      recoveryTime: null
    };
    
    try {
      // Classify the error
      errorInfo.classification = await this.classifyError(error, context);
      
      // Update error metrics
      await this.updateErrorMetrics(errorInfo);
      
      // Check circuit breaker status
      const circuitBreakerStatus = await this.checkCircuitBreaker(context.service);
      
      if (circuitBreakerStatus.state === 'OPEN') {
        throw new Error(`Circuit breaker is OPEN for service: ${context.service}`);
      }
      
      // Determine recovery strategy
      errorInfo.recoveryStrategy = await this.determineRecoveryStrategy(errorInfo);
      
      // Execute recovery
      const recoveryResult = await this.executeRecovery(errorInfo);
      
      if (recoveryResult.success) {
        errorInfo.recovered = true;
        errorInfo.recoveryTime = Date.now() - timestamp;
        
        // Update circuit breaker on success
        await this.updateCircuitBreakerSuccess(context.service);
        
        console.log(`✅ Error recovered: ${errorId} in ${errorInfo.recoveryTime}ms`);
        this.emit('errorRecovered', errorInfo);
      } else {
        errorInfo.recovered = false;
        
        // Update circuit breaker on failure
        await this.updateCircuitBreakerFailure(context.service);
        
        console.error(`❌ Error recovery failed: ${errorId}`);
        this.emit('errorRecoveryFailed', errorInfo);
      }
      
      // Store error information
      this.errorPatterns.set(errorId, errorInfo);
      
      return errorInfo;
      
    } catch (recoveryError) {
      console.error('❌ Error handling system failure:', recoveryError.message);
      
      // Fallback error handling
      return await this.fallbackErrorHandling(error, context);
    }
  }

  /**
   * Classify error type for appropriate handling
   */
  async classifyError(error, context) {
    const classification = {
      type: 'UNKNOWN',
      severity: 'MEDIUM',
      retryable: false,
      confidence: 0.5,
      patterns: []
    };
    
    // Pattern-based classification
    const errorMessage = error.message.toLowerCase();
    const errorCode = error.code;
    
    // Network-related errors
    if (errorMessage.includes('timeout') || errorMessage.includes('network') || errorCode === 'ETIMEDOUT') {
      classification.type = 'TRANSIENT';
      classification.severity = 'LOW';
      classification.retryable = true;
      classification.confidence = 0.9;
      classification.patterns.push('network_timeout');
    }
    
    // Authentication errors
    else if (errorMessage.includes('unauthorized') || errorMessage.includes('authentication') || errorCode === 401) {
      classification.type = 'PERMANENT';
      classification.severity = 'HIGH';
      classification.retryable = false;
      classification.confidence = 0.95;
      classification.patterns.push('authentication_failed');
    }
    
    // Database errors
    else if (errorMessage.includes('database') || errorMessage.includes('connection') || errorCode === 'ECONNREFUSED') {
      classification.type = 'INTERMITTENT';
      classification.severity = 'HIGH';
      classification.retryable = true;
      classification.confidence = 0.8;
      classification.patterns.push('database_connection');
    }
    
    // Rate limiting errors
    else if (errorMessage.includes('rate limit') || errorCode === 429) {
      classification.type = 'TRANSIENT';
      classification.severity = 'MEDIUM';
      classification.retryable = true;
      classification.confidence = 0.9;
      classification.patterns.push('rate_limit');
    }
    
    // Security-related errors
    else if (errorMessage.includes('security') || errorMessage.includes('breach') || errorMessage.includes('attack')) {
      classification.type = 'CRITICAL';
      classification.severity = 'CRITICAL';
      classification.retryable = false;
      classification.confidence = 0.85;
      classification.patterns.push('security_breach');
    }
    
    // Use AI-based classification for unknown errors
    if (classification.type === 'UNKNOWN') {
      const aiClassification = await this.aiClassifyError(error, context);
      Object.assign(classification, aiClassification);
    }
    
    return classification;
  }

  /**
   * Determine optimal recovery strategy
   */
  async determineRecoveryStrategy(errorInfo) {
    const strategies = [];
    
    const { classification, context } = errorInfo;
    
    // Strategy selection based on error type
    switch (classification.type) {
      case 'TRANSIENT':
        strategies.push('intelligent_retry');
        if (context.service) {
          strategies.push('load_balancing');
        }
        break;
        
      case 'INTERMITTENT':
        strategies.push('circuit_breaker');
        strategies.push('fallback_service');
        break;
        
      case 'PERMANENT':
        strategies.push('graceful_degradation');
        if (classification.patterns.includes('authentication_failed')) {
          strategies.push('token_refresh');
        }
        break;
        
      case 'CRITICAL':
        strategies.push('emergency_shutdown');
        strategies.push('security_lockdown');
        break;
    }
    
    // Add service-specific strategies
    if (context.service === 'database') {
      strategies.push('connection_pool_reset');
    } else if (context.service === 'cache') {
      strategies.push('cache_invalidation');
    } else if (context.service === 'payment') {
      strategies.push('payment_retry');
    }
    
    return {
      primary: strategies[0] || 'default_retry',
      fallback: strategies.slice(1),
      confidence: classification.confidence
    };
  }

  /**
   * Execute recovery strategy
   */
  async executeRecovery(errorInfo) {
    const { recoveryStrategy, context } = errorInfo;
    const startTime = Date.now();
    
    const recoveryResult = {
      strategy: recoveryStrategy.primary,
      success: false,
      attempts: 0,
      duration: 0,
      fallbackUsed: false,
      details: {}
    };
    
    try {
      // Try primary recovery strategy
      const primaryResult = await this.executeRecoveryStrategy(
        recoveryStrategy.primary,
        errorInfo
      );
      
      recoveryResult.attempts++;
      recoveryResult.details.primary = primaryResult;
      
      if (primaryResult.success) {
        recoveryResult.success = true;
      } else {
        // Try fallback strategies
        for (const fallbackStrategy of recoveryStrategy.fallback) {
          const fallbackResult = await this.executeRecoveryStrategy(
            fallbackStrategy,
            errorInfo
          );
          
          recoveryResult.attempts++;
          recoveryResult.details[fallbackStrategy] = fallbackResult;
          
          if (fallbackResult.success) {
            recoveryResult.success = true;
            recoveryResult.fallbackUsed = true;
            recoveryResult.strategy = fallbackStrategy;
            break;
          }
        }
      }
      
      recoveryResult.duration = Date.now() - startTime;
      
      return recoveryResult;
      
    } catch (error) {
      recoveryResult.duration = Date.now() - startTime;
      recoveryResult.error = error.message;
      
      return recoveryResult;
    }
  }

  /**
   * Execute specific recovery strategy
   */
  async executeRecoveryStrategy(strategy, errorInfo) {
    const strategyFunction = this.recoveryStrategies.get(strategy);
    
    if (!strategyFunction) {
      return {
        success: false,
        error: `Unknown recovery strategy: ${strategy}`
      };
    }
    
    try {
      const result = await strategyFunction(errorInfo);
      
      return {
        success: true,
        result,
        strategy
      };
    } catch (error) {
      return {
        success: false,
        error: error.message,
        strategy
      };
    }
  }

  /**
   * Circuit breaker implementation
   */
  async checkCircuitBreaker(serviceName) {
    if (!serviceName) return { state: 'CLOSED' };
    
    const circuitBreaker = this.circuitBreakers.get(serviceName);
    
    if (!circuitBreaker) {
      return { state: 'CLOSED' };
    }
    
    const now = Date.now();
    
    // Check if circuit breaker should transition from OPEN to HALF_OPEN
    if (circuitBreaker.state === 'OPEN') {
      if (now - circuitBreaker.lastFailureTime > circuitBreaker.timeout) {
        circuitBreaker.state = 'HALF_OPEN';
        circuitBreaker.successCount = 0;
        console.log(`🔄 Circuit breaker HALF_OPEN for service: ${serviceName}`);
      }
    }
    
    return circuitBreaker;
  }

  /**
   * Update circuit breaker on success
   */
  async updateCircuitBreakerSuccess(serviceName) {
    if (!serviceName) return;
    
    const circuitBreaker = this.circuitBreakers.get(serviceName);
    
    if (!circuitBreaker) return;
    
    if (circuitBreaker.state === 'HALF_OPEN') {
      circuitBreaker.successCount++;
      
      if (circuitBreaker.successCount >= circuitBreaker.halfOpenMaxCalls) {
        circuitBreaker.state = 'CLOSED';
        circuitBreaker.failureCount = 0;
        console.log(`✅ Circuit breaker CLOSED for service: ${serviceName}`);
      }
    } else if (circuitBreaker.state === 'CLOSED') {
      circuitBreaker.failureCount = Math.max(0, circuitBreaker.failureCount - 1);
    }
  }

  /**
   * Update circuit breaker on failure
   */
  async updateCircuitBreakerFailure(serviceName) {
    if (!serviceName) return;
    
    const circuitBreaker = this.circuitBreakers.get(serviceName);
    
    if (!circuitBreaker) return;
    
    circuitBreaker.failureCount++;
    circuitBreaker.lastFailureTime = Date.now();
    
    if (circuitBreaker.state === 'CLOSED' && circuitBreaker.failureCount >= circuitBreaker.threshold) {
      circuitBreaker.state = 'OPEN';
      console.log(`🚨 Circuit breaker OPEN for service: ${serviceName}`);
      this.emit('circuitBreakerOpened', { serviceName, circuitBreaker });
    } else if (circuitBreaker.state === 'HALF_OPEN') {
      circuitBreaker.state = 'OPEN';
      console.log(`🚨 Circuit breaker OPEN (from HALF_OPEN) for service: ${serviceName}`);
    }
  }

  /**
   * Recovery strategy implementations
   */
  async restartService(errorInfo) {
    const serviceName = errorInfo.context.service;
    console.log(`🔄 Restarting service: ${serviceName}`);
    
    // Simulate service restart
    await new Promise(resolve => setTimeout(resolve, 2000));
    
    return {
      action: 'service_restart',
      service: serviceName,
      success: Math.random() > 0.2 // 80% success rate
    };
  }
  
  async activateFallbackService(errorInfo) {
    const serviceName = errorInfo.context.service;
    console.log(`🔀 Activating fallback for service: ${serviceName}`);
    
    return {
      action: 'fallback_activation',
      service: serviceName,
      fallbackEndpoint: `fallback-${serviceName}`,
      success: true
    };
  }
  
  async activateCircuitBreaker(errorInfo) {
    const serviceName = errorInfo.context.service;
    console.log(`⚡ Activating circuit breaker for service: ${serviceName}`);
    
    await this.updateCircuitBreakerFailure(serviceName);
    
    return {
      action: 'circuit_breaker_activation',
      service: serviceName,
      success: true
    };
  }
  
  async enableGracefulDegradation(errorInfo) {
    console.log('📉 Enabling graceful degradation');
    
    return {
      action: 'graceful_degradation',
      features_disabled: ['advanced_analytics', 'real_time_updates'],
      success: true
    };
  }
  
  async emergencyShutdown(errorInfo) {
    console.log('🚨 Initiating emergency shutdown');
    
    return {
      action: 'emergency_shutdown',
      affected_services: ['all_non_critical'],
      success: true
    };
  }
  
  async initiateDataRecovery(errorInfo) {
    console.log('💾 Initiating data recovery');
    
    return {
      action: 'data_recovery',
      backup_source: 'latest_backup',
      success: Math.random() > 0.1 // 90% success rate
    };
  }
  
  async redistributeLoad(errorInfo) {
    console.log('⚖️ Redistributing load');
    
    return {
      action: 'load_redistribution',
      target_nodes: ['node-2', 'node-3'],
      success: true
    };
  }
  
  async invalidateCache(errorInfo) {
    console.log('🗑️ Invalidating cache');
    
    return {
      action: 'cache_invalidation',
      cache_keys_cleared: 150,
      success: true
    };
  }

  /**
   * AI-based error classification
   */
  async aiClassifyError(error, context) {
    // Simplified AI classification
    const features = {
      messageLength: error.message.length,
      hasStackTrace: !!error.stack,
      errorCode: error.code || 'none',
      serviceName: context.service || 'unknown'
    };
    
    // Simple heuristic-based classification
    let type = 'UNKNOWN';
    let confidence = 0.5;
    
    if (features.messageLength > 100 && features.hasStackTrace) {
      type = 'CRITICAL';
      confidence = 0.7;
    } else if (features.errorCode.includes('TIMEOUT')) {
      type = 'TRANSIENT';
      confidence = 0.8;
    } else if (features.serviceName === 'database') {
      type = 'INTERMITTENT';
      confidence = 0.6;
    }
    
    return {
      type,
      severity: type === 'CRITICAL' ? 'CRITICAL' : 'MEDIUM',
      retryable: type !== 'PERMANENT',
      confidence,
      patterns: [`ai_classified_${type.toLowerCase()}`]
    };
  }

  /**
   * Update error metrics
   */
  async updateErrorMetrics(errorInfo) {
    const globalMetrics = this.errorMetrics.get('global');
    
    globalMetrics.totalErrors++;
    
    if (errorInfo.classification.severity === 'CRITICAL') {
      globalMetrics.criticalErrors++;
    }
    
    // Update error rate (errors per minute)
    const now = Date.now();
    const windowStart = now - this.errorConfig.errorAggregationWindow;
    
    const recentErrors = Array.from(this.errorPatterns.values())
      .filter(e => e.timestamp > windowStart);
    
    globalMetrics.errorRate = recentErrors.length / (this.errorConfig.errorAggregationWindow / 60000);
    
    // Update error by type
    const errorType = errorInfo.classification.type;
    const typeCount = globalMetrics.errorsByType.get(errorType) || 0;
    globalMetrics.errorsByType.set(errorType, typeCount + 1);
    
    // Update error by service
    const serviceName = errorInfo.context.service;
    const serviceCount = globalMetrics.errorsByService.get(serviceName) || 0;
    globalMetrics.errorsByService.set(serviceName, serviceCount + 1);
  }

  /**
   * Fallback error handling
   */
  async fallbackErrorHandling(error, context) {
    console.log('🆘 Using fallback error handling');
    
    return {
      id: this.generateErrorId(),
      timestamp: Date.now(),
      error: {
        message: error.message,
        name: error.name
      },
      context,
      classification: {
        type: 'UNKNOWN',
        severity: 'MEDIUM',
        retryable: false,
        confidence: 0.1
      },
      recovered: false,
      fallbackUsed: true
    };
  }

  /**
   * Start error monitoring
   */
  startErrorMonitoring() {
    // Monitor error patterns every minute
    setInterval(() => {
      this.analyzeErrorPatterns();
    }, 60000);
    
    // Check circuit breaker health every 30 seconds
    setInterval(() => {
      this.monitorCircuitBreakers();
    }, 30000);
    
    console.log('🛡️ Error monitoring started');
  }

  /**
   * Analyze error patterns for insights
   */
  async analyzeErrorPatterns() {
    const recentErrors = Array.from(this.errorPatterns.values())
      .filter(e => Date.now() - e.timestamp < 300000); // Last 5 minutes
    
    if (recentErrors.length === 0) return;
    
    const patterns = {
      totalErrors: recentErrors.length,
      errorsByType: new Map(),
      errorsByService: new Map(),
      recoveryRate: 0,
      averageRecoveryTime: 0
    };
    
    let totalRecoveryTime = 0;
    let recoveredCount = 0;
    
    for (const error of recentErrors) {
      // Count by type
      const type = error.classification.type;
      patterns.errorsByType.set(type, (patterns.errorsByType.get(type) || 0) + 1);
      
      // Count by service
      const service = error.context.service;
      patterns.errorsByService.set(service, (patterns.errorsByService.get(service) || 0) + 1);
      
      // Calculate recovery metrics
      if (error.recovered) {
        recoveredCount++;
        totalRecoveryTime += error.recoveryTime;
      }
    }
    
    patterns.recoveryRate = recoveredCount / recentErrors.length;
    patterns.averageRecoveryTime = recoveredCount > 0 ? totalRecoveryTime / recoveredCount : 0;
    
    this.emit('errorPatternsAnalyzed', patterns);
    
    // Alert on high error rates
    if (patterns.totalErrors > 10) {
      this.emit('highErrorRateDetected', patterns);
    }
  }

  /**
   * Monitor circuit breaker health
   */
  async monitorCircuitBreakers() {
    const circuitBreakerStatus = {
      total: this.circuitBreakers.size,
      closed: 0,
      open: 0,
      halfOpen: 0
    };
    
    for (const [serviceName, circuitBreaker] of this.circuitBreakers.entries()) {
      switch (circuitBreaker.state) {
        case 'CLOSED':
          circuitBreakerStatus.closed++;
          break;
        case 'OPEN':
          circuitBreakerStatus.open++;
          break;
        case 'HALF_OPEN':
          circuitBreakerStatus.halfOpen++;
          break;
      }
    }
    
    this.emit('circuitBreakerStatus', circuitBreakerStatus);
  }

  /**
   * Utility methods
   */
  generateErrorId() {
    return 'ERR_' + Date.now() + '_' + randomBytes(4).toString('hex').toUpperCase();
  }
  
  /**
   * Get error handling statistics
   */
  getErrorHandlingStats() {
    const globalMetrics = this.errorMetrics.get('global');
    
    return {
      errorMetrics: {
        totalErrors: globalMetrics.totalErrors,
        errorRate: globalMetrics.errorRate,
        criticalErrors: globalMetrics.criticalErrors,
        recoveryRate: globalMetrics.recoveredErrors / Math.max(1, globalMetrics.totalErrors)
      },
      circuitBreakers: {
        total: this.circuitBreakers.size,
        states: Array.from(this.circuitBreakers.values()).reduce((acc, cb) => {
          acc[cb.state] = (acc[cb.state] || 0) + 1;
          return acc;
        }, {})
      },
      recoveryStrategies: {
        available: this.recoveryStrategies.size,
        mostUsed: 'service_restart' // Simplified
      },
      errorPatterns: {
        total: this.errorPatterns.size,
        recentPatterns: Array.from(this.errorPatterns.values()).slice(-10).length
      }
    };
  }
}
