const axios = require('axios');
const os = require('os');
const fs = require('fs').promises;
const path = require('path');
const nodemailer = require('nodemailer');
const logger = require('./logger');

/**
 * Health check utility for monitoring all system dependencies
 */
class HealthCheck {
  constructor() {
    this.services = {
      nocodb: { name: 'NocoDB', healthy: false, lastCheck: null, details: {} },
      smtp: { name: 'SMTP Server', healthy: false, lastCheck: null, details: {} },
      representAPI: { name: 'Represent API', healthy: false, lastCheck: null, details: {} },
      disk: { name: 'Disk Space', healthy: false, lastCheck: null, details: {} },
      memory: { name: 'Memory', healthy: false, lastCheck: null, details: {} },
    };
  }

  /**
   * Check NocoDB connectivity and API health
   */
  async checkNocoDB() {
    const start = Date.now();
    try {
      const response = await axios.get(`${process.env.NOCODB_API_URL}/db/meta/projects`, {
        headers: {
          'xc-token': process.env.NOCODB_API_TOKEN
        },
        timeout: 5000
      });

      const duration = Date.now() - start;
      this.services.nocodb = {
        name: 'NocoDB',
        healthy: response.status === 200,
        lastCheck: new Date().toISOString(),
        details: {
          status: response.status,
          responseTime: `${duration}ms`,
          url: process.env.NOCODB_API_URL
        }
      };

      logger.logHealthCheck('nocodb', 'healthy', { responseTime: duration });
      return this.services.nocodb;
    } catch (error) {
      this.services.nocodb = {
        name: 'NocoDB',
        healthy: false,
        lastCheck: new Date().toISOString(),
        details: {
          error: error.message,
          url: process.env.NOCODB_API_URL
        }
      };

      logger.logHealthCheck('nocodb', 'unhealthy', { error: error.message });
      return this.services.nocodb;
    }
  }

  /**
   * Check SMTP server connectivity
   */
  async checkSMTP() {
    const start = Date.now();
    
    // Skip SMTP check if in test mode
    if (process.env.EMAIL_TEST_MODE === 'true') {
      this.services.smtp = {
        name: 'SMTP Server',
        healthy: true,
        lastCheck: new Date().toISOString(),
        details: {
          mode: 'test',
          message: 'SMTP test mode enabled - emails logged only'
        }
      };
      return this.services.smtp;
    }

    try {
      const transporter = nodemailer.createTransport({
        host: process.env.SMTP_HOST,
        port: parseInt(process.env.SMTP_PORT || '587'),
        secure: process.env.SMTP_SECURE === 'true',
        auth: {
          user: process.env.SMTP_USER,
          pass: process.env.SMTP_PASS
        },
        connectionTimeout: 5000
      });

      await transporter.verify();
      const duration = Date.now() - start;

      this.services.smtp = {
        name: 'SMTP Server',
        healthy: true,
        lastCheck: new Date().toISOString(),
        details: {
          host: process.env.SMTP_HOST,
          port: process.env.SMTP_PORT,
          responseTime: `${duration}ms`
        }
      };

      logger.logHealthCheck('smtp', 'healthy', { responseTime: duration });
      return this.services.smtp;
    } catch (error) {
      this.services.smtp = {
        name: 'SMTP Server',
        healthy: false,
        lastCheck: new Date().toISOString(),
        details: {
          error: error.message,
          host: process.env.SMTP_HOST
        }
      };

      logger.logHealthCheck('smtp', 'unhealthy', { error: error.message });
      return this.services.smtp;
    }
  }

  /**
   * Check Represent API availability
   */
  async checkRepresentAPI() {
    const start = Date.now();
    const testUrl = `${process.env.REPRESENT_API_BASE || 'https://represent.opennorth.ca'}/representatives/house-of-commons/`;
    
    try {
      const response = await axios.get(testUrl, {
        timeout: 5000
      });

      const duration = Date.now() - start;
      this.services.representAPI = {
        name: 'Represent API',
        healthy: response.status === 200,
        lastCheck: new Date().toISOString(),
        details: {
          status: response.status,
          responseTime: `${duration}ms`,
          url: testUrl
        }
      };

      logger.logHealthCheck('represent-api', 'healthy', { responseTime: duration });
      return this.services.representAPI;
    } catch (error) {
      this.services.representAPI = {
        name: 'Represent API',
        healthy: false,
        lastCheck: new Date().toISOString(),
        details: {
          error: error.message,
          url: testUrl
        }
      };

      logger.logHealthCheck('represent-api', 'unhealthy', { error: error.message });
      return this.services.representAPI;
    }
  }

  /**
   * Check disk space for uploads directory
   */
  async checkDiskSpace() {
    try {
      const uploadsDir = path.join(__dirname, '../public/uploads');
      
      // Ensure directory exists
      try {
        await fs.access(uploadsDir);
      } catch {
        await fs.mkdir(uploadsDir, { recursive: true });
      }

      // Get directory size
      const directorySize = await this.getDirectorySize(uploadsDir);
      
      // Get system disk usage (platform-specific approximation)
      const freeSpace = os.freemem();
      const totalSpace = os.totalmem();
      const usedPercentage = ((totalSpace - freeSpace) / totalSpace) * 100;

      // Consider healthy if less than 90% full
      const healthy = usedPercentage < 90;

      this.services.disk = {
        name: 'Disk Space',
        healthy,
        lastCheck: new Date().toISOString(),
        details: {
          uploadsSize: this.formatBytes(directorySize),
          systemUsedPercentage: `${usedPercentage.toFixed(2)}%`,
          freeSpace: this.formatBytes(freeSpace),
          totalSpace: this.formatBytes(totalSpace),
          path: uploadsDir
        }
      };

      logger.logHealthCheck('disk', healthy ? 'healthy' : 'unhealthy', this.services.disk.details);
      return this.services.disk;
    } catch (error) {
      this.services.disk = {
        name: 'Disk Space',
        healthy: false,
        lastCheck: new Date().toISOString(),
        details: {
          error: error.message
        }
      };

      logger.logHealthCheck('disk', 'unhealthy', { error: error.message });
      return this.services.disk;
    }
  }

  /**
   * Check memory usage
   */
  async checkMemory() {
    try {
      const totalMemory = os.totalmem();
      const freeMemory = os.freemem();
      const usedMemory = totalMemory - freeMemory;
      const usedPercentage = (usedMemory / totalMemory) * 100;

      // Get Node.js process memory
      const processMemory = process.memoryUsage();

      // Consider healthy if less than 85% used
      const healthy = usedPercentage < 85;

      this.services.memory = {
        name: 'Memory',
        healthy,
        lastCheck: new Date().toISOString(),
        details: {
          system: {
            total: this.formatBytes(totalMemory),
            used: this.formatBytes(usedMemory),
            free: this.formatBytes(freeMemory),
            usedPercentage: `${usedPercentage.toFixed(2)}%`
          },
          process: {
            rss: this.formatBytes(processMemory.rss),
            heapTotal: this.formatBytes(processMemory.heapTotal),
            heapUsed: this.formatBytes(processMemory.heapUsed),
            external: this.formatBytes(processMemory.external)
          }
        }
      };

      logger.logHealthCheck('memory', healthy ? 'healthy' : 'unhealthy', this.services.memory.details);
      return this.services.memory;
    } catch (error) {
      this.services.memory = {
        name: 'Memory',
        healthy: false,
        lastCheck: new Date().toISOString(),
        details: {
          error: error.message
        }
      };

      logger.logHealthCheck('memory', 'unhealthy', { error: error.message });
      return this.services.memory;
    }
  }

  /**
   * Run all health checks
   */
  async checkAll() {
    const results = await Promise.allSettled([
      this.checkNocoDB(),
      this.checkSMTP(),
      this.checkRepresentAPI(),
      this.checkDiskSpace(),
      this.checkMemory()
    ]);

    const overall = {
      status: Object.values(this.services).every(s => s.healthy) ? 'healthy' : 'degraded',
      timestamp: new Date().toISOString(),
      services: this.services,
      uptime: process.uptime(),
      version: process.env.npm_package_version || '1.0.0',
      environment: process.env.NODE_ENV || 'development'
    };

    // Check if any critical services are down
    // Note: In development, NocoDB might not be available yet
    // Only mark as unhealthy if multiple critical services fail
    const criticalServices = ['nocodb'];
    const criticalDown = criticalServices.filter(name => !this.services[name].healthy);
    
    // Allow degraded state if only external services (NocoDB, Represent API) are down
    // Only fail health check if core services (disk, memory) are unhealthy
    const coreServicesHealthy = this.services.disk.healthy && this.services.memory.healthy;
    
    if (!coreServicesHealthy) {
      overall.status = 'unhealthy';
    } else if (criticalDown.length > 0) {
      // Mark as degraded (not unhealthy) if external services are down
      // This allows the container to start even if NocoDB isn't ready
      overall.status = 'degraded';
    }

    return overall;
  }

  /**
   * Get health check for a specific service
   */
  async checkService(serviceName) {
    const checkMethods = {
      nocodb: () => this.checkNocoDB(),
      smtp: () => this.checkSMTP(),
      representAPI: () => this.checkRepresentAPI(),
      disk: () => this.checkDiskSpace(),
      memory: () => this.checkMemory()
    };

    if (checkMethods[serviceName]) {
      return await checkMethods[serviceName]();
    }

    throw new Error(`Unknown service: ${serviceName}`);
  }

  /**
   * Helper: Get directory size recursively
   */
  async getDirectorySize(directory) {
    let size = 0;
    
    try {
      const files = await fs.readdir(directory);
      
      for (const file of files) {
        const filePath = path.join(directory, file);
        const stats = await fs.stat(filePath);
        
        if (stats.isDirectory()) {
          size += await this.getDirectorySize(filePath);
        } else {
          size += stats.size;
        }
      }
    } catch (error) {
      logger.warn(`Error calculating directory size: ${error.message}`);
    }
    
    return size;
  }

  /**
   * Helper: Format bytes to human readable
   */
  formatBytes(bytes) {
    if (bytes === 0) return '0 Bytes';
    
    const k = 1024;
    const sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB'];
    const i = Math.floor(Math.log(bytes) / Math.log(k));
    
    return parseFloat((bytes / Math.pow(k, i)).toFixed(2)) + ' ' + sizes[i];
  }
}

module.exports = new HealthCheck();