/**
 * Health Check Dashboard Module
 * Monitors service health, response times, and uptime
 * Provides SLA tracking and incident management
 */

const https = require('https');
const http = require('http');
const EventEmitter = require('events');
const fs = require('fs');
const path = require('path');

const HEALTH_CONFIG_FILE = process.env.HEALTH_CONFIG_FILE || path.join(__dirname, 'health-config.json');
const HEALTH_HISTORY_FILE = process.env.HEALTH_HISTORY_FILE || path.join(__dirname, 'health-history.json');
const CHECK_INTERVAL = parseInt(process.env.HEALTH_CHECK_INTERVAL || '30000', 10); // 30 seconds
const MAX_CHECK_INTERVAL = parseInt(process.env.HEALTH_CHECK_MAX_INTERVAL || '300000', 10); // 5 minutes max backoff
const HISTORY_RETENTION_DAYS = parseInt(process.env.HEALTH_HISTORY_RETENTION || '30', 10);

class HealthChecker extends EventEmitter {
  constructor() {
    super();
    this.config = this.loadConfig();
    this.history = this.loadHistory();
    this.currentStatus = new Map();
    this.incidents = [];
    this.checking = false;
    this.checkInterval = null;
    this.consecutiveFailures = new Map(); // serviceId -> failure count
    this.serviceTimers = new Map(); // serviceId -> timer for per-service backoff
  }

  /**
   * Start health checking
   */
  start() {
    if (this.checking) return;

    this.checking = true;

    // Initial check
    this.checkAll();

    // Schedule periodic checks
    this.checkInterval = setInterval(() => this.checkAll(), CHECK_INTERVAL);
  }

  /**
   * Stop health checking
   */
  stop() {
    if (!this.checking) return;

    this.checking = false;

    if (this.checkInterval) {
      clearInterval(this.checkInterval);
      this.checkInterval = null;
    }

    // Clear per-service backoff timers
    for (const timer of this.serviceTimers.values()) {
      clearTimeout(timer);
    }
    this.serviceTimers.clear();
  }

  /**
   * Get the backoff interval for a service based on consecutive failures.
   * Doubles the interval for each failure, capped at MAX_CHECK_INTERVAL.
   */
  getBackoffInterval(serviceId) {
    const failures = this.consecutiveFailures.get(serviceId) || 0;
    if (failures === 0) return CHECK_INTERVAL;
    return Math.min(CHECK_INTERVAL * Math.pow(2, failures), MAX_CHECK_INTERVAL);
  }

  /**
   * Check all configured services
   */
  async checkAll() {
    const services = Object.entries(this.config.services || {});
    
    for (const [serviceId, config] of services) {
      if (config.enabled !== false) {
        try {
          await this.checkService(serviceId, config);
        } catch (error) {
          // Error logged via checkForIncidents
        }
      }
    }
    
    // Cleanup old history
    this.cleanupHistory();
  }

  /**
   * Check a single service
   */
  async checkService(serviceId, config) {
    const startTime = Date.now();

    try {
      const result = await this.performHealthCheck(config);
      const responseTime = Date.now() - startTime;

      const status = {
        serviceId,
        timestamp: new Date().toISOString(),
        status: result.healthy ? 'up' : 'down',
        responseTime,
        statusCode: result.statusCode,
        message: result.message,
        details: result.details
      };

      // Track consecutive failures for exponential backoff
      if (result.healthy) {
        this.consecutiveFailures.delete(serviceId);
      } else {
        this.consecutiveFailures.set(serviceId, (this.consecutiveFailures.get(serviceId) || 0) + 1);
      }

      this.recordStatus(serviceId, status);
      this.checkForIncidents(serviceId, status, config);

      return status;
    } catch (error) {
      const responseTime = Date.now() - startTime;

      // Increment failure count for backoff
      this.consecutiveFailures.set(serviceId, (this.consecutiveFailures.get(serviceId) || 0) + 1);

      const status = {
        serviceId,
        timestamp: new Date().toISOString(),
        status: 'down',
        responseTime,
        error: error.message
      };

      this.recordStatus(serviceId, status);
      this.checkForIncidents(serviceId, status, config);

      return status;
    }
  }

  /**
   * Perform actual health check
   */
  async performHealthCheck(config) {
    const result = await this._doRequest(config, config.method || 'GET');
    // Fall back to GET if HEAD is not supported
    if ((result.statusCode === 501 || result.statusCode === 405) && (config.method || '').toUpperCase() === 'HEAD') {
      return this._doRequest({ ...config, method: 'GET' }, 'GET');
    }
    return result;
  }

  _doRequest(config, method) {
    return new Promise((resolve, reject) => {
      const url = new URL(config.url);
      const protocol = url.protocol === 'https:' ? https : http;

      const options = {
        hostname: url.hostname,
        port: url.port || (url.protocol === 'https:' ? 443 : 80),
        path: url.pathname + url.search,
        method,
        timeout: config.timeout || 20000,
        headers: config.headers || {},
        rejectUnauthorized: false // Trust internal CA certs (.sami TLD)
      };

      const req = protocol.request(options, (res) => {
        let data = '';

        res.on('data', chunk => {
          data += chunk;
        });

        res.on('end', () => {
          const healthy = this.evaluateHealth(res.statusCode, data, config);

          resolve({
            healthy,
            statusCode: res.statusCode,
            message: healthy ? 'Service is healthy' : 'Service check failed',
            details: {
              headers: res.headers,
              bodyLength: data.length
            }
          });
        });
      });

      req.on('error', (error) => {
        reject(error);
      });

      req.on('timeout', () => {
        req.destroy();
        reject(new Error('Health check timeout'));
      });

      if (config.body) {
        req.write(JSON.stringify(config.body));
      }

      req.end();
    });
  }

  /**
   * Evaluate if service is healthy based on response
   */
  evaluateHealth(statusCode, body, config) {
    // Check status code
    const expectedCodes = config.expectedStatusCodes || [200, 201, 204, 301, 302, 303, 307, 308];
    if (!expectedCodes.includes(statusCode)) {
      return false;
    }

    // Check response body if pattern specified
    if (config.expectedBodyPattern) {
      const regex = new RegExp(config.expectedBodyPattern);
      if (!regex.test(body)) {
        return false;
      }
    }

    // Check response body contains expected text
    if (config.expectedBodyContains) {
      if (!body.includes(config.expectedBodyContains)) {
        return false;
      }
    }

    return true;
  }

  /**
   * Record service status
   */
  recordStatus(serviceId, status) {
    // Update current status
    this.currentStatus.set(serviceId, status);

    // Add to history
    if (!this.history[serviceId]) {
      this.history[serviceId] = [];
    }

    this.history[serviceId].push(status);

    // Emit status event
    this.emit('status-check', status);

    // Save history periodically
    if (Math.random() < 0.05) { // 5% chance (every ~20 checks)
      this.saveHistory();
    }
  }

  /**
   * Check for incidents (downtime, slow response, etc.)
   */
  checkForIncidents(serviceId, status, config) {
    const previous = this.currentStatus.get(serviceId);
    
    // Check for status change (up -> down or down -> up)
    if (previous && previous.status !== status.status) {
      if (status.status === 'down') {
        this.createIncident(serviceId, 'outage', 'Service is down', status);
      } else if (status.status === 'up') {
        this.resolveIncident(serviceId, 'outage', status);
      }
    }

    // Check for slow response time
    const slowThreshold = config.slowResponseThreshold || 5000; // 5 seconds
    if (status.responseTime > slowThreshold) {
      this.createIncident(serviceId, 'slow-response', 
        `Response time ${status.responseTime}ms exceeds threshold ${slowThreshold}ms`, 
        status);
    }

    // Check SLA violations
    const sla = config.sla;
    if (sla) {
      const uptime = this.calculateUptime(serviceId, sla.period || 24);
      if (uptime < sla.target) {
        this.createIncident(serviceId, 'sla-violation',
          `Uptime ${uptime.toFixed(2)}% below SLA target ${sla.target}%`,
          status);
      }
    }
  }

  /**
   * Create a new incident
   */
  createIncident(serviceId, type, message, status) {
    // Check if similar incident already exists
    const existing = this.incidents.find(i => 
      i.serviceId === serviceId && 
      i.type === type && 
      i.status === 'open'
    );

    if (existing) {
      // Update existing incident
      existing.lastOccurrence = status.timestamp;
      existing.occurrences++;
      return;
    }

    // Create new incident
    const incident = {
      id: `incident-${Date.now()}-${Math.random().toString(36).substr(2, 9)}`,
      serviceId,
      type,
      message,
      status: 'open',
      severity: this.calculateSeverity(type),
      createdAt: status.timestamp,
      lastOccurrence: status.timestamp,
      occurrences: 1,
      details: status
    };

    this.incidents.push(incident);
    this.emit('incident-created', incident);
    
    this.emit('log', 'info', `Incident created: ${incident.id} - ${message}`);
  }

  /**
   * Resolve an incident
   */
  resolveIncident(serviceId, type, status) {
    const incident = this.incidents.find(i => 
      i.serviceId === serviceId && 
      i.type === type && 
      i.status === 'open'
    );

    if (incident) {
      incident.status = 'resolved';
      incident.resolvedAt = status.timestamp;
      incident.duration = new Date(incident.resolvedAt) - new Date(incident.createdAt);
      
      this.emit('incident-resolved', incident);
      this.emit('log', 'info', `Incident resolved: ${incident.id}`);
    }
  }

  /**
   * Calculate incident severity
   */
  calculateSeverity(type) {
    switch (type) {
      case 'outage':
        return 'critical';
      case 'sla-violation':
        return 'high';
      case 'slow-response':
        return 'medium';
      default:
        return 'low';
    }
  }

  /**
   * Calculate uptime percentage for a service
   */
  calculateUptime(serviceId, hours = 24) {
    const history = this.getServiceHistory(serviceId, hours);
    if (history.length === 0) return 100;

    const upChecks = history.filter(h => h.status === 'up').length;
    return (upChecks / history.length) * 100;
  }

  /**
   * Calculate average response time
   */
  calculateAverageResponseTime(serviceId, hours = 24) {
    const history = this.getServiceHistory(serviceId, hours);
    if (history.length === 0) return 0;

    const total = history.reduce((sum, h) => sum + (h.responseTime || 0), 0);
    return total / history.length;
  }

  /**
   * Get service history for specified time period
   */
  getServiceHistory(serviceId, hours = 24) {
    const cutoffTime = Date.now() - (hours * 60 * 60 * 1000);
    const history = this.history[serviceId] || [];
    
    return history.filter(h => 
      new Date(h.timestamp).getTime() > cutoffTime
    );
  }

  /**
   * Get current status for all services
   */
  getCurrentStatus() {
    const result = {};
    
    for (const [serviceId, status] of this.currentStatus.entries()) {
      const config = this.config.services[serviceId];
      const uptime24h = this.calculateUptime(serviceId, 24);
      const uptime7d = this.calculateUptime(serviceId, 168);
      const avgResponseTime = this.calculateAverageResponseTime(serviceId, 24);
      
      result[serviceId] = {
        ...status,
        name: config?.name || serviceId,
        uptime: {
          '24h': uptime24h,
          '7d': uptime7d
        },
        avgResponseTime,
        sla: config?.sla
      };
    }
    
    return result;
  }

  /**
   * Get service statistics
   */
  getServiceStats(serviceId, hours = 24) {
    const history = this.getServiceHistory(serviceId, hours);
    if (history.length === 0) return null;

    const upChecks = history.filter(h => h.status === 'up').length;
    const downChecks = history.length - upChecks;
    const responseTimes = history.map(h => h.responseTime || 0);
    
    return {
      serviceId,
      period: `${hours}h`,
      totalChecks: history.length,
      upChecks,
      downChecks,
      uptime: (upChecks / history.length) * 100,
      responseTime: {
        avg: responseTimes.reduce((a, b) => a + b, 0) / responseTimes.length,
        min: Math.min(...responseTimes),
        max: Math.max(...responseTimes),
        p95: this.calculatePercentile(responseTimes, 95),
        p99: this.calculatePercentile(responseTimes, 99)
      }
    };
  }

  /**
   * Calculate percentile
   */
  calculatePercentile(values, percentile) {
    const sorted = values.slice().sort((a, b) => a - b);
    const index = Math.ceil((percentile / 100) * sorted.length) - 1;
    return sorted[index] || 0;
  }

  /**
   * Get open incidents
   */
  getOpenIncidents() {
    return this.incidents.filter(i => i.status === 'open');
  }

  /**
   * Get incident history
   */
  getIncidentHistory(limit = 50) {
    return this.incidents.slice(-limit).reverse();
  }

  /**
   * Configure health check for a service
   */
  configureService(serviceId, config) {
    if (!this.config.services) {
      this.config.services = {};
    }

    this.config.services[serviceId] = {
      enabled: config.enabled !== false,
      name: config.name || serviceId,
      url: config.url,
      method: config.method || 'GET',
      timeout: config.timeout || 20000,
      expectedStatusCodes: config.expectedStatusCodes || [200],
      expectedBodyPattern: config.expectedBodyPattern,
      expectedBodyContains: config.expectedBodyContains,
      slowResponseThreshold: config.slowResponseThreshold || 5000,
      sla: config.sla,
      headers: config.headers || {},
      body: config.body
    };

    this.saveConfig();
  }

  /**
   * Remove service configuration
   */
  removeService(serviceId) {
    if (this.config.services) {
      delete this.config.services[serviceId];
      this.saveConfig();
    }

    this.currentStatus.delete(serviceId);
    delete this.history[serviceId];
  }

  /**
   * Cleanup old history
   */
  cleanupHistory() {
    const cutoffTime = Date.now() - (HISTORY_RETENTION_DAYS * 24 * 60 * 60 * 1000);
    
    for (const serviceId in this.history) {
      this.history[serviceId] = this.history[serviceId].filter(h =>
        new Date(h.timestamp).getTime() > cutoffTime
      );
    }
  }

  /**
   * Load configuration
   */
  loadConfig() {
    try {
      if (fs.existsSync(HEALTH_CONFIG_FILE)) {
        return JSON.parse(fs.readFileSync(HEALTH_CONFIG_FILE, 'utf8'));
      }
    } catch (error) {
      this.emit('log', 'error', `Error loading config: ${error.message}`);
    }
    return { services: {} };
  }

  /**
   * Save configuration
   */
  saveConfig() {
    try {
      fs.writeFileSync(HEALTH_CONFIG_FILE, JSON.stringify(this.config, null, 2));
    } catch (error) {
      this.emit('log', 'error', `Error saving config: ${error.message}`);
    }
  }

  /**
   * Load history
   */
  loadHistory() {
    try {
      if (fs.existsSync(HEALTH_HISTORY_FILE)) {
        return JSON.parse(fs.readFileSync(HEALTH_HISTORY_FILE, 'utf8'));
      }
    } catch (error) {
      this.emit('log', 'error', `Error loading history: ${error.message}`);
    }
    return {};
  }

  /**
   * Save history
   */
  saveHistory() {
    try {
      fs.writeFileSync(HEALTH_HISTORY_FILE, JSON.stringify(this.history, null, 2));
    } catch (error) {
      this.emit('log', 'error', `Error saving history: ${error.message}`);
    }
  }
}

// Export singleton instance
module.exports = new HealthChecker();