/**
 * Shattered Void MMO - Health Monitoring System
 * 
 * This module provides comprehensive health monitoring for all game services,
 * including real-time status checks, performance metrics, and alerting.
 */

const http = require('http');
const { EventEmitter } = require('events');
const os = require('os');

class HealthMonitor extends EventEmitter {
  constructor(options = {}) {
    super();
    
    this.services = options.services || {};
    this.interval = options.interval || 30000; // 30 seconds
    this.onHealthChange = options.onHealthChange || null;
    this.timeout = options.timeout || 5000; // 5 seconds
    
    this.healthStatus = {};
    this.metrics = {};
    this.alertThresholds = {
      responseTime: 5000,    // 5 seconds
      memoryUsage: 80,       // 80%
      cpuUsage: 90,          // 90%
      errorRate: 10          // 10%
    };
    
    this.monitoringInterval = null;
    this.isRunning = false;
    this.healthHistory = {};
    
    // Initialize health status for all services
    this.initializeHealthStatus();
  }

  /**
   * Initialize health status tracking
   */
  initializeHealthStatus() {
    Object.keys(this.services).forEach(serviceName => {
      this.healthStatus[serviceName] = {
        status: 'unknown',
        lastCheck: null,
        responseTime: null,
        consecutiveFailures: 0,
        uptime: 0,
        lastError: null
      };
      
      this.healthHistory[serviceName] = [];
    });
  }

  /**
   * Start health monitoring
   */
  async start() {
    if (this.isRunning) {
      throw new Error('Health monitor is already running');
    }
    
    this.isRunning = true;
    console.log(`🏥 Health monitoring started (interval: ${this.interval}ms)`);
    
    // Initial health check
    await this.performHealthChecks();
    
    // Start periodic monitoring
    this.monitoringInterval = setInterval(async () => {
      try {
        await this.performHealthChecks();
      } catch (error) {
        console.error('Health check error:', error);
      }
    }, this.interval);
    
    // Start system metrics monitoring
    this.startSystemMetricsMonitoring();
    
    this.emit('started');
  }

  /**
   * Stop health monitoring
   */
  stop() {
    if (!this.isRunning) {
      return;
    }
    
    this.isRunning = false;
    
    if (this.monitoringInterval) {
      clearInterval(this.monitoringInterval);
      this.monitoringInterval = null;
    }
    
    console.log('🏥 Health monitoring stopped');
    this.emit('stopped');
  }

  /**
   * Perform health checks on all services
   */
  async performHealthChecks() {
    const checkPromises = Object.entries(this.services).map(([serviceName, serviceInfo]) => {
      return this.checkServiceHealth(serviceName, serviceInfo);
    });
    
    await Promise.allSettled(checkPromises);
    this.updateHealthSummary();
  }

  /**
   * Check health of a specific service
   */
  async checkServiceHealth(serviceName, serviceInfo) {
    const startTime = Date.now();
    const previousStatus = this.healthStatus[serviceName].status;
    
    try {
      let isHealthy = false;
      let responseTime = null;
      
      // Different health check strategies based on service type
      switch (serviceName) {
        case 'backend':
          isHealthy = await this.checkHttpService(serviceInfo.port, '/health');
          responseTime = Date.now() - startTime;
          break;
          
        case 'frontend':
          isHealthy = await this.checkHttpService(serviceInfo.port);
          responseTime = Date.now() - startTime;
          break;
          
        case 'database':
          isHealthy = await this.checkDatabaseHealth();
          responseTime = Date.now() - startTime;
          break;
          
        case 'redis':
          isHealthy = await this.checkRedisHealth();
          responseTime = Date.now() - startTime;
          break;
          
        default:
          // For other services, assume healthy if they exist
          isHealthy = true;
          responseTime = Date.now() - startTime;
      }
      
      // Update health status
      const newStatus = isHealthy ? 'healthy' : 'unhealthy';
      this.updateServiceStatus(serviceName, {
        status: newStatus,
        lastCheck: new Date(),
        responseTime,
        consecutiveFailures: isHealthy ? 0 : this.healthStatus[serviceName].consecutiveFailures + 1,
        lastError: null
      });
      
      // Emit health change event if status changed
      if (previousStatus !== newStatus && this.onHealthChange) {
        this.onHealthChange(serviceName, newStatus);
      }
      
    } catch (error) {
      const responseTime = Date.now() - startTime;
      
      this.updateServiceStatus(serviceName, {
        status: 'unhealthy',
        lastCheck: new Date(),
        responseTime,
        consecutiveFailures: this.healthStatus[serviceName].consecutiveFailures + 1,
        lastError: error.message
      });
      
      // Emit health change event if status changed
      if (previousStatus !== 'unhealthy' && this.onHealthChange) {
        this.onHealthChange(serviceName, 'unhealthy');
      }
      
      console.error(`Health check failed for ${serviceName}:`, error.message);
    }
  }

  /**
   * Check HTTP service health
   */
  checkHttpService(port, path = '/') {
    return new Promise((resolve, reject) => {
      const options = {
        hostname: 'localhost',
        port: port,
        path: path,
        method: 'GET',
        timeout: this.timeout
      };
      
      const req = http.request(options, (res) => {
        // Consider 2xx and 3xx status codes as healthy
        resolve(res.statusCode >= 200 && res.statusCode < 400);
      });
      
      req.on('error', (error) => {
        reject(error);
      });
      
      req.on('timeout', () => {
        req.destroy();
        reject(new Error('Request timeout'));
      });
      
      req.end();
    });
  }

  /**
   * Check database health
   */
  async checkDatabaseHealth() {
    try {
      // Try to get database connection from the app
      const db = require('../src/database/connection');
      
      // Simple query to check database connectivity
      await db.raw('SELECT 1');
      return true;
    } catch (error) {
      return false;
    }
  }

  /**
   * Check Redis health
   */
  async checkRedisHealth() {
    try {
      // Skip if Redis is disabled
      if (process.env.DISABLE_REDIS === 'true') {
        return true;
      }
      
      // Try to get Redis client from the app
      const redisConfig = require('../src/config/redis');
      
      if (!redisConfig.client) {
        return false;
      }
      
      // Simple ping to check Redis connectivity
      await redisConfig.client.ping();
      return true;
    } catch (error) {
      return false;
    }
  }

  /**
   * Update service status
   */
  updateServiceStatus(serviceName, statusUpdate) {
    this.healthStatus[serviceName] = {
      ...this.healthStatus[serviceName],
      ...statusUpdate
    };
    
    // Add to health history
    this.addToHealthHistory(serviceName, statusUpdate);
    
    // Check for alerts
    this.checkForAlerts(serviceName);
  }

  /**
   * Add health data to history
   */
  addToHealthHistory(serviceName, statusData) {
    const historyEntry = {
      timestamp: Date.now(),
      status: statusData.status,
      responseTime: statusData.responseTime,
      error: statusData.lastError
    };
    
    this.healthHistory[serviceName].push(historyEntry);
    
    // Keep only last 100 entries
    if (this.healthHistory[serviceName].length > 100) {
      this.healthHistory[serviceName] = this.healthHistory[serviceName].slice(-100);
    }
  }

  /**
   * Check for health alerts
   */
  checkForAlerts(serviceName) {
    const health = this.healthStatus[serviceName];
    const alerts = [];
    
    // Check consecutive failures
    if (health.consecutiveFailures >= 3) {
      alerts.push({
        type: 'consecutive_failures',
        message: `Service ${serviceName} has failed ${health.consecutiveFailures} consecutive times`,
        severity: 'critical'
      });
    }
    
    // Check response time
    if (health.responseTime && health.responseTime > this.alertThresholds.responseTime) {
      alerts.push({
        type: 'slow_response',
        message: `Service ${serviceName} response time: ${health.responseTime}ms (threshold: ${this.alertThresholds.responseTime}ms)`,
        severity: 'warning'
      });
    }
    
    // Emit alerts
    alerts.forEach(alert => {
      this.emit('alert', serviceName, alert);
    });
  }

  /**
   * Start system metrics monitoring
   */
  startSystemMetricsMonitoring() {
    const updateSystemMetrics = () => {
      const memUsage = process.memoryUsage();
      const cpuUsage = process.cpuUsage();
      const systemMem = {
        total: os.totalmem(),
        free: os.freemem()
      };
      
      this.metrics.system = {
        timestamp: Date.now(),
        memory: {
          rss: memUsage.rss,
          heapTotal: memUsage.heapTotal,
          heapUsed: memUsage.heapUsed,
          external: memUsage.external,
          usage: Math.round((memUsage.heapUsed / memUsage.heapTotal) * 100)
        },
        cpu: {
          user: cpuUsage.user,
          system: cpuUsage.system
        },
        systemMemory: {
          total: systemMem.total,
          free: systemMem.free,
          used: systemMem.total - systemMem.free,
          usage: Math.round(((systemMem.total - systemMem.free) / systemMem.total) * 100)
        },
        uptime: process.uptime(),
        loadAverage: os.loadavg()
      };
      
      // Check for system alerts
      this.checkSystemAlerts();
    };
    
    // Update immediately
    updateSystemMetrics();
    
    // Update every 10 seconds
    setInterval(updateSystemMetrics, 10000);
  }

  /**
   * Check for system-level alerts
   */
  checkSystemAlerts() {
    const metrics = this.metrics.system;
    
    if (!metrics) return;
    
    // Memory usage alert
    if (metrics.memory.usage > this.alertThresholds.memoryUsage) {
      this.emit('alert', 'system', {
        type: 'high_memory_usage',
        message: `High memory usage: ${metrics.memory.usage}% (threshold: ${this.alertThresholds.memoryUsage}%)`,
        severity: 'warning'
      });
    }
    
    // System memory alert
    if (metrics.systemMemory.usage > this.alertThresholds.memoryUsage) {
      this.emit('alert', 'system', {
        type: 'high_system_memory',
        message: `High system memory usage: ${metrics.systemMemory.usage}% (threshold: ${this.alertThresholds.memoryUsage}%)`,
        severity: 'critical'
      });
    }
  }

  /**
   * Update overall health summary
   */
  updateHealthSummary() {
    const services = Object.keys(this.healthStatus);
    const healthyServices = services.filter(s => this.healthStatus[s].status === 'healthy');
    const unhealthyServices = services.filter(s => this.healthStatus[s].status === 'unhealthy');
    
    this.metrics.summary = {
      timestamp: Date.now(),
      totalServices: services.length,
      healthyServices: healthyServices.length,
      unhealthyServices: unhealthyServices.length,
      overallHealth: unhealthyServices.length === 0 ? 'healthy' : 'degraded'
    };
  }

  /**
   * Get current health status
   */
  getHealthStatus() {
    return {
      services: this.healthStatus,
      metrics: this.metrics,
      summary: this.metrics.summary,
      isRunning: this.isRunning
    };
  }

  /**
   * Get health history for a service
   */
  getHealthHistory(serviceName) {
    return this.healthHistory[serviceName] || [];
  }

  /**
   * Get service uptime
   */
  getServiceUptime(serviceName) {
    const history = this.healthHistory[serviceName];
    if (!history || history.length === 0) {
      return 0;
    }
    
    const now = Date.now();
    const oneDayAgo = now - (24 * 60 * 60 * 1000);
    
    const recentHistory = history.filter(entry => entry.timestamp > oneDayAgo);
    
    if (recentHistory.length === 0) {
      return 0;
    }
    
    const healthyCount = recentHistory.filter(entry => entry.status === 'healthy').length;
    return Math.round((healthyCount / recentHistory.length) * 100);
  }

  /**
   * Generate health report
   */
  generateHealthReport() {
    const services = Object.keys(this.healthStatus);
    const report = {
      timestamp: new Date().toISOString(),
      summary: this.metrics.summary,
      services: {},
      systemMetrics: this.metrics.system,
      alerts: []
    };
    
    services.forEach(serviceName => {
      const health = this.healthStatus[serviceName];
      const uptime = this.getServiceUptime(serviceName);
      
      report.services[serviceName] = {
        status: health.status,
        lastCheck: health.lastCheck,
        responseTime: health.responseTime,
        consecutiveFailures: health.consecutiveFailures,
        uptime: `${uptime}%`,
        lastError: health.lastError
      };
    });
    
    return report;
  }

  /**
   * Export health data for monitoring systems
   */
  exportMetrics() {
    return {
      timestamp: Date.now(),
      services: this.healthStatus,
      system: this.metrics.system,
      summary: this.metrics.summary,
      uptime: Object.keys(this.healthStatus).reduce((acc, serviceName) => {
        acc[serviceName] = this.getServiceUptime(serviceName);
        return acc;
      }, {})
    };
  }
}

module.exports = HealthMonitor;