const express = require('express');
const http = require('http');
const socketIo = require('socket.io');
const cors = require('cors');
const helmet = require('helmet');
const morgan = require('morgan');
const rateLimit = require('express-rate-limit');
const { createProxyMiddleware } = require('http-proxy-middleware');
const jwt = require('jsonwebtoken');
const axios = require('axios');
require('dotenv').config();

// Import middleware
const authMiddleware = require('./middleware/authentication');
const serviceHealthMiddleware = require('./middleware/serviceHealth');
const requestLogger = require('./middleware/requestLogger');
const websocketAuth = require('./middleware/webSocket');

// Import route handlers
const serviceRouter = require('./routes/serviceRouter');
const healthRouter = require('./routes/healthRouter');
const websocketRouter = require('./routes/websocketRouter');

const app = express();
const server = http.createServer(app);
const PORT = process.env.PORT || 8000;

// Initialize Socket.IO with CORS
const io = socketIo(server, {
  cors: {
    origin: process.env.FRONTEND_URL || "*",
    credentials: true,
    methods: ['GET', 'POST']
  },
  transports: ['websocket', 'polling']
});

// Make io available globally for other modules
global.io = io;

// Service targets configuration
const serviceTargets = {
  USER_AUTH_URL: process.env.USER_AUTH_URL || 'http://localhost:8011',
  TEMPLATE_MANAGER_URL: process.env.TEMPLATE_MANAGER_URL || 'http://localhost:8009',
  REQUIREMENT_PROCESSOR_URL: process.env.REQUIREMENT_PROCESSOR_URL || 'http://localhost:8001',
  TECH_STACK_SELECTOR_URL: process.env.TECH_STACK_SELECTOR_URL || 'http://localhost:8002',
  ARCHITECTURE_DESIGNER_URL: process.env.ARCHITECTURE_DESIGNER_URL || 'http://localhost:8003',
  CODE_GENERATOR_URL: process.env.CODE_GENERATOR_URL || 'http://localhost:8004',
  TEST_GENERATOR_URL: process.env.TEST_GENERATOR_URL || 'http://localhost:8005',
  DEPLOYMENT_MANAGER_URL: process.env.DEPLOYMENT_MANAGER_URL || 'http://localhost:8006',
  DASHBOARD_URL: process.env.DASHBOARD_URL || 'http://localhost:8008',
  SELF_IMPROVING_GENERATOR_URL: process.env.SELF_IMPROVING_GENERATOR_URL || 'http://localhost:8007',
};

// ========================================
// MIDDLEWARE SETUP
// ========================================

// Security middleware
app.use(helmet({
  contentSecurityPolicy: {
    directives: {
      defaultSrc: ["'self'"],
      styleSrc: ["'self'", "'unsafe-inline'"],
      scriptSrc: ["'self'"],
      imgSrc: ["'self'", "data:", "https:"],
      connectSrc: ["'self'", "ws:", "wss:"]
    }
  }
}));

// CORS configuration
app.use(cors({
  origin: process.env.FRONTEND_URL || "*",
  credentials: true,
  optionsSuccessStatus: 200,
  methods: ['GET', 'POST', 'PUT', 'DELETE', 'OPTIONS'],
  allowedHeaders: [
    'Origin', 'X-Requested-With', 'Content-Type', 'Accept', 'Authorization',
    'X-Gateway-Request-ID', 'X-Gateway-Timestamp', 'X-Forwarded-By', 
    'X-Forwarded-For', 'X-Forwarded-Proto', 'X-Forwarded-Host',
    'X-Session-Token', 'X-Platform', 'X-App-Version'
  ],
  exposedHeaders: [
    'X-Gateway-Request-ID', 'X-Gateway-Timestamp', 'X-Forwarded-By', 
    'X-Forwarded-For', 'X-Forwarded-Proto', 'X-Forwarded-Host'
  ]
}));

// Request parsing middleware - only for non-proxy routes
app.use('/api/websocket', express.json({ limit: '10mb' }));
app.use('/api/gateway', express.json({ limit: '10mb' }));
app.use('/api/auth', express.json({ limit: '10mb' }));
app.use('/api/templates', express.json({ limit: '10mb' }));
app.use('/api/features', express.json({ limit: '10mb' }));
app.use('/health', express.json({ limit: '10mb' }));

// Trust proxy for accurate IP addresses
app.set('trust proxy', 1);

// Request ID middleware for tracing
app.use((req, res, next) => {
  req.requestId = `gw-${Date.now()}-${Math.random().toString(36).substr(2, 9)}`;
  res.setHeader('X-Request-ID', req.requestId);
  next();
});

app.use(morgan(process.env.NODE_ENV === 'production' ? 'combined' : 'dev'));

// Custom request logger for service tracking
app.use(requestLogger.logRequest);

// Rate limiting configuration
const createServiceLimiter = (maxRequests = 1000) => rateLimit({
  windowMs: parseInt(process.env.RATE_LIMIT_WINDOW_MS) || 15 * 60 * 1000,
  max: maxRequests,
  message: {
    success: false,
    message: 'Too many requests, please try again later.',
    retry_after: 900
  },
  standardHeaders: true,
  legacyHeaders: false
});

// Health check endpoint (before rate limiting and authentication)
app.get('/health', (req, res) => {
  res.json({
    success: true,
    service: 'api-gateway',
    status: 'healthy',
    timestamp: new Date().toISOString(),
    version: process.env.npm_package_version || '1.0.0',
    environment: process.env.NODE_ENV || 'development',
    uptime: process.uptime(),
    services: {
      user_auth: process.env.USER_AUTH_URL ? 'configured' : 'not configured',
      template_manager: process.env.TEMPLATE_MANAGER_URL ? 'configured' : 'not configured',
      requirement_processor: process.env.REQUIREMENT_PROCESSOR_URL ? 'configured' : 'not configured',
      tech_stack_selector: process.env.TECH_STACK_SELECTOR_URL ? 'configured' : 'not configured',
      architecture_designer: process.env.ARCHITECTURE_DESIGNER_URL ? 'configured' : 'not configured',
      code_generator: process.env.CODE_GENERATOR_URL ? 'configured' : 'not configured',
      test_generator: process.env.TEST_GENERATOR_URL ? 'configured' : 'not configured',
      deployment_manager: process.env.DEPLOYMENT_MANAGER_URL ? 'configured' : 'not configured',
      dashboard: process.env.DASHBOARD_URL ? 'configured' : 'not configured',
      self_improving_generator: process.env.SELF_IMPROVING_GENERATOR_URL ? 'configured' : 'not configured'
    },
    websocket: 'enabled'
  });
});

// Service health monitoring routes
app.use('/health', healthRouter.router);

// WebSocket connection handling
const websocketHandlers = websocketAuth(io);

// Auth Service - Fixed proxy with proper connection handling
console.log('🔧 Registering /api/auth proxy route...');
app.use('/api/auth', (req, res, next) => {
  const authServiceUrl = serviceTargets.USER_AUTH_URL;
  console.log(`🔥 [AUTH PROXY] ${req.method} ${req.originalUrl} → ${authServiceUrl}${req.originalUrl}`);
  
  // Set response timeout to prevent hanging
  res.setTimeout(15000, () => {
    console.error('❌ [AUTH PROXY] Response timeout');
    if (!res.headersSent) {
      res.status(504).json({ error: 'Gateway timeout', service: 'user-auth' });
    }
  });

  const options = {
    method: req.method,
    url: `${authServiceUrl}${req.originalUrl}`,
    headers: {
      'Content-Type': 'application/json',
      'User-Agent': 'API-Gateway/1.0',
      'Connection': 'keep-alive'
    },
    timeout: 8000,
    validateStatus: () => true,
    maxRedirects: 0
  };

  // Always include request body for POST/PUT/PATCH requests
  if (req.method === 'POST' || req.method === 'PUT' || req.method === 'PATCH') {
    options.data = req.body || {};
    console.log(`📦 [AUTH PROXY] Request body:`, JSON.stringify(req.body));
  }

  axios(options)
    .then(response => {
      console.log(`✅ [AUTH PROXY] Response: ${response.status} for ${req.method} ${req.originalUrl}`);
      if (!res.headersSent) {
        res.status(response.status).json(response.data);
      }
    })
    .catch(error => {
      console.error(`❌ [AUTH PROXY ERROR]:`, error.message);
      if (!res.headersSent) {
        if (error.response) {
          res.status(error.response.status).json(error.response.data);
        } else {
          res.status(502).json({ 
            error: 'Auth service unavailable', 
            message: error.code || error.message,
            service: 'user-auth'
          });
        }
      }
    });
});

// WebSocket API routes for managing connections
app.use('/api/websocket', websocketRouter);

// Apply rate limiting to other API routes
app.use('/api', createServiceLimiter(1000));

// Template Manager Service - Direct HTTP forwarding
console.log('🔧 Registering /api/templates proxy route...');
app.use('/api/templates', 
  createServiceLimiter(200),
  // Conditionally require auth: allow public GETs, require token for write ops
  (req, res, next) => {
    if (req.method === 'GET') {
      return next();
    }
    return authMiddleware.verifyToken(req, res, () => authMiddleware.forwardUserContext(req, res, next));
  },
  (req, res, next) => {
    const templateServiceUrl = serviceTargets.TEMPLATE_MANAGER_URL;
    console.log(`🔥 [TEMPLATE PROXY] ${req.method} ${req.originalUrl} → ${templateServiceUrl}${req.originalUrl}`);
    
    // Set response timeout to prevent hanging
    res.setTimeout(15000, () => {
      console.error('❌ [TEMPLATE PROXY] Response timeout');
      if (!res.headersSent) {
        res.status(504).json({ error: 'Gateway timeout', service: 'template-manager' });
      }
    });

    const options = {
      method: req.method,
      url: `${templateServiceUrl}${req.originalUrl}`,
      headers: {
        'Content-Type': 'application/json',
        'User-Agent': 'API-Gateway/1.0',
        'Connection': 'keep-alive',
        // Forward user context from auth middleware
        'X-User-ID': req.user?.id || req.user?.userId,
        'X-User-Role': req.user?.role,
        'Authorization': req.headers.authorization
      },
      timeout: 8000,
      validateStatus: () => true,
      maxRedirects: 0
    };

    // Always include request body for POST/PUT/PATCH requests
    if (req.method === 'POST' || req.method === 'PUT' || req.method === 'PATCH') {
      options.data = req.body || {};
      console.log(`📦 [TEMPLATE PROXY] Request body:`, JSON.stringify(req.body));
    }

    axios(options)
      .then(response => {
        console.log(`✅ [TEMPLATE PROXY] Response: ${response.status} for ${req.method} ${req.originalUrl}`);
        if (!res.headersSent) {
          res.status(response.status).json(response.data);
        }
      })
      .catch(error => {
        console.error(`❌ [TEMPLATE PROXY ERROR]:`, error.message);
        if (!res.headersSent) {
          if (error.response) {
            res.status(error.response.status).json(error.response.data);
          } else {
            res.status(502).json({ 
              error: 'Template service unavailable', 
              message: error.code || error.message,
              service: 'template-manager'
            });
          }
        }
      });
  }
);

// Requirement Processor Service
app.use('/api/requirements', 
  createServiceLimiter(300),
  authMiddleware.verifyToken,
  authMiddleware.forwardUserContext,
  serviceRouter.createServiceProxy(serviceTargets.REQUIREMENT_PROCESSOR_URL, 'requirement-processor')
);

// Tech Stack Selector Service
app.use('/api/tech-stack', 
  createServiceLimiter(200),
  authMiddleware.verifyToken,
  authMiddleware.forwardUserContext,
  serviceRouter.createServiceProxy(serviceTargets.TECH_STACK_SELECTOR_URL, 'tech-stack-selector')
);

// Architecture Designer Service
app.use('/api/architecture', 
  createServiceLimiter(150),
  authMiddleware.verifyToken,
  authMiddleware.forwardUserContext,
  serviceRouter.createServiceProxy(serviceTargets.ARCHITECTURE_DESIGNER_URL, 'architecture-designer')
);

// Code Generator Service
app.use('/api/codegen', 
  createServiceLimiter(100),
  authMiddleware.verifyToken,
  authMiddleware.forwardUserContext,
  serviceRouter.createServiceProxy(serviceTargets.CODE_GENERATOR_URL, 'code-generator')
);

// Test Generator Service
app.use('/api/tests', 
  createServiceLimiter(150),
  authMiddleware.verifyToken,
  authMiddleware.forwardUserContext,
  serviceRouter.createServiceProxy(serviceTargets.TEST_GENERATOR_URL, 'test-generator')
);

// Deployment Manager Service
app.use('/api/deploy', 
  createServiceLimiter(100),
  authMiddleware.verifyToken,
  authMiddleware.forwardUserContext,
  serviceRouter.createServiceProxy(serviceTargets.DEPLOYMENT_MANAGER_URL, 'deployment-manager')
);

// Dashboard Service
app.use('/api/dashboard', 
  createServiceLimiter(300),
  authMiddleware.verifyToken,
  authMiddleware.forwardUserContext,
  serviceRouter.createServiceProxy(serviceTargets.DASHBOARD_URL, 'dashboard')
);

// Self-Improving Generator Service
app.use('/api/self-improving', 
  createServiceLimiter(50),
  authMiddleware.verifyToken,
  authMiddleware.forwardUserContext,
  serviceRouter.createServiceProxy(serviceTargets.SELF_IMPROVING_GENERATOR_URL, 'self-improving-generator')
);

// Features (Template Manager) - expose /api/features via gateway
console.log('🔧 Registering /api/features proxy route...');
app.use('/api/features',
  createServiceLimiter(300),
  (req, res, next) => {
    if (req.method === 'GET') {
      return next();
    }
    return authMiddleware.verifyToken(req, res, () => authMiddleware.forwardUserContext(req, res, next));
  },
  (req, res, next) => {
    const templateServiceUrl = serviceTargets.TEMPLATE_MANAGER_URL;
    console.log(`🔥 [FEATURES PROXY] ${req.method} ${req.originalUrl} → ${templateServiceUrl}${req.originalUrl}`);

    res.setTimeout(15000, () => {
      console.error('❌ [FEATURES PROXY] Response timeout');
      if (!res.headersSent) {
        res.status(504).json({ error: 'Gateway timeout', service: 'template-manager' });
      }
    });

    const options = {
      method: req.method,
      url: `${templateServiceUrl}${req.originalUrl}`,
      headers: {
        'Content-Type': 'application/json',
        'User-Agent': 'API-Gateway/1.0',
        'Connection': 'keep-alive',
        'Authorization': req.headers.authorization,
        'X-User-ID': req.user?.id || req.user?.userId,
        'X-User-Role': req.user?.role,
      },
      timeout: 8000,
      validateStatus: () => true,
      maxRedirects: 0
    };

    if (req.method === 'POST' || req.method === 'PUT' || req.method === 'PATCH') {
      options.data = req.body || {};
      console.log(`📦 [FEATURES PROXY] Request body:`, JSON.stringify(req.body));
    }

    axios(options)
      .then(response => {
        console.log(`✅ [FEATURES PROXY] Response: ${response.status} for ${req.method} ${req.originalUrl}`);
        if (!res.headersSent) {
          res.status(response.status).json(response.data);
        }
      })
      .catch(error => {
        console.error(`❌ [FEATURES PROXY ERROR]:`, error.message);
        if (!res.headersSent) {
          if (error.response) {
            res.status(error.response.status).json(error.response.data);
          } else {
            res.status(502).json({
              error: 'Template feature service unavailable',
              message: error.code || error.message,
              service: 'template-manager'
            });
          }
        }
      });
  }
);

// Gateway management endpoints
app.get('/api/gateway/info', authMiddleware.verifyToken, (req, res) => {
  res.json({
    success: true,
    gateway: {
      name: 'CodeNuk API Gateway',
      version: process.env.npm_package_version || '1.0.0',
      environment: process.env.NODE_ENV || 'development',
      uptime: process.uptime()
    },
    services: {
      total_services: Object.keys(serviceTargets).length,
      operational_services: Object.keys(serviceTargets).length,
      service_urls: serviceTargets
    },
    features: {
      websocket_enabled: true,
      authentication: true,
      rate_limiting: true,
      health_monitoring: true,
      request_logging: true,
      cors_enabled: true
    },
    websocket: {
      connected_clients: io.engine.clientsCount,
      transport_types: ['websocket', 'polling']
    }
  });
});

// Service status endpoint
app.get('/api/gateway/services', authMiddleware.verifyToken, serviceHealthMiddleware.getServiceStatus);

// Root endpoint
app.get('/', (req, res) => {
  res.json({
    success: true,
    message: 'CodeNuk API Gateway',
    version: process.env.npm_package_version || '1.0.0',
    description: 'Central gateway for all CodeNuk microservices',
    documentation: {
      health: '/health',
      gateway_info: '/api/gateway/info',
      service_status: '/api/gateway/services'
    },
    services: {
      auth: '/api/auth',
      templates: '/api/templates',
      requirements: '/api/requirements',
      tech_stack: '/api/tech-stack',
      architecture: '/api/architecture',
      codegen: '/api/codegen',
      tests: '/api/tests',
      deploy: '/api/deploy',
      dashboard: '/api/dashboard',
      self_improving: '/api/self-improving'
    },
    websocket: {
      endpoint: '/socket.io/',
      authentication_required: true
    }
  });
});

// 404 handler
app.use('*', (req, res) => {
  res.status(404).json({
    success: false,
    message: 'Endpoint not found',
    available_services: {
      auth: '/api/auth',
      templates: '/api/templates',
      requirements: '/api/requirements',
      tech_stack: '/api/tech-stack',
      architecture: '/api/architecture',
      codegen: '/api/codegen',
      tests: '/api/tests',
      deploy: '/api/deploy',
      dashboard: '/api/dashboard',
      self_improving: '/api/self-improving'
    },
    documentation: '/api/gateway/info'
  });
});

// Global error handler
app.use((error, req, res, next) => {
  console.error(`[${req.requestId}] Gateway Error:`, error);
  
  // Handle proxy errors
  if (error.code === 'ECONNREFUSED' || error.code === 'ENOTFOUND') {
    return res.status(503).json({
      success: false,
      message: 'Service temporarily unavailable',
      error: 'The requested service is currently unavailable',
      request_id: req.requestId
    });
  }

  // Handle timeout errors
  if (error.code === 'ETIMEDOUT' || error.message.includes('timeout')) {
    return res.status(504).json({
      success: false,
      message: 'Service timeout',
      error: 'The service took too long to respond',
      request_id: req.requestId
    });
  }

  // Handle authentication errors
  if (error.name === 'JsonWebTokenError' || error.name === 'TokenExpiredError') {
    return res.status(401).json({
      success: false,
      message: 'Authentication failed',
      error: error.message
    });
  }

  // Generic error handler
  res.status(error.status || 500).json({
    success: false,
    message: error.message || 'Internal gateway error',
    error: process.env.NODE_ENV === 'development' ? {
      stack: error.stack,
      name: error.name
    } : undefined,
    request_id: req.requestId
  });
});

// Start server and initialize health monitoring
const startServer = async () => {
  try {
    console.log('🚀 Starting CodeNuk API Gateway...');
    
    // Initialize service health monitoring
    await serviceHealthMiddleware.initializeHealthMonitoring();
    
    server.listen(PORT, '0.0.0.0', () => {
      console.log(`✅ API Gateway running on port ${PORT}`);
      console.log(`🌍 Environment: ${process.env.NODE_ENV || 'development'}`);
      console.log(`📋 Health check: http://localhost:${PORT}/health`);
      console.log(`📖 Gateway info: http://localhost:${PORT}/api/gateway/info`);
      console.log(`🔗 WebSocket enabled on: ws://localhost:${PORT}`);
      
      // Log service configuration
      console.log('⚙️  Configured Services:');
      Object.entries(serviceTargets).forEach(([name, url]) => {
        console.log(`   - ${name}: ${url}`);
      });
      
      console.log('🔧 Features:');
      console.log(`   - Rate Limiting: Enabled`);
      console.log(`   - Authentication: JWT with Auth Service`);
      console.log(`   - WebSocket: Real-time notifications`);
      console.log(`   - Health Monitoring: All services`);
      console.log(`   - Request Logging: Enabled`);
    });

  } catch (error) {
    console.error('❌ Failed to start API Gateway:', error);
    process.exit(1);
  }
};

// Graceful shutdown
process.on('SIGTERM', () => {
  console.log('📴 SIGTERM received, shutting down gracefully...');
  server.close(() => {
    console.log('✅ API Gateway shut down successfully');
    process.exit(0);
  });
});

process.on('SIGINT', () => {
  console.log('📴 SIGINT received, shutting down gracefully...');
  server.close(() => {
    console.log('✅ API Gateway shut down successfully');
    process.exit(0);
  });
});

// Start the server
startServer();

module.exports = app;