const express = require('express');
const webpush = require('web-push');
const cors = require('cors');
const fs = require('fs');
const path = require('path');
const dns = require('dns'); // Add DNS module

// Load environment variables from .env file
require('dotenv').config();

// --- Configuration ---
const port = process.env.PORT || 3000;
const vapidPublicKey = process.env.VAPID_PUBLIC_KEY;
const vapidPrivateKey = process.env.VAPID_PRIVATE_KEY;
const vapidSubject = process.env.VAPID_SUBJECT; // mailto: or https:
const subscriptionsFilePath = process.env.SUBSCRIPTIONS_FILE || path.join(__dirname, 'subscriptions.json');
// Basic Authentication Credentials
const basicAuthUsername = process.env.BASIC_AUTH_USERNAME;
const basicAuthPassword = process.env.BASIC_AUTH_PASSWORD;
// Note: We are NOT adding specific authentication for the /subscribe endpoint in this version.
// Consider adding API key or other auth if exposing this publicly.
const allowedOrigins = (process.env.ALLOWED_ORIGINS || "").split(',').map(origin => origin.trim()).filter(origin => origin);
const allowedMethods = (process.env.ALLOWED_METHODS || "POST,OPTIONS,GET").split(',').map(method => method.trim()).filter(method => method);
const allowedHeaders = (process.env.ALLOWED_HEADERS || "Content-Type,Authorization").split(',').map(header => header.trim()).filter(header => header);
// Retry configuration for DNS resolution issues
const maxRetries = parseInt(process.env.MAX_NOTIFICATION_RETRIES || 3, 10);
const initialRetryDelay = parseInt(process.env.INITIAL_RETRY_DELAY_MS || 1000, 10); // 1 second
// HTTP request timeout configuration
const httpTimeout = parseInt(process.env.HTTP_TIMEOUT_MS || 10000, 10); // 10 seconds
// Logging level configuration
const LOG_LEVEL = (process.env.LOG_LEVEL || 'info').toLowerCase();

// --- Logging Utility ---
const LogLevels = {
  error: 0,
  warn: 1,
  info: 2,
  debug: 3
};

const logger = {
  error: (...args) => {
    console.error(...args);
  },
  warn: (...args) => {
    if (LogLevels[LOG_LEVEL] >= LogLevels.warn) {
      console.warn(...args);
    }
  },
  info: (...args) => {
    if (LogLevels[LOG_LEVEL] >= LogLevels.info) {
      console.log(...args);
    }
  },
  debug: (...args) => {
    if (LogLevels[LOG_LEVEL] >= LogLevels.debug) {
      console.log('DEBUG -', ...args);
    }
  }
};

// Configure global HTTP agent with timeouts to prevent hanging requests
const https = require('https');
const http = require('http');

// Custom HTTPS agent with timeout
const httpsAgent = new https.Agent({
  keepAlive: true,
  timeout: httpTimeout,
  maxSockets: 50, // Limit concurrent connections
});

// Apply the agent to the webpush module if possible
// Note: The web-push library might use its own agent, but this is a precaution
https.globalAgent = httpsAgent;

// --- Validation ---
if (!vapidPublicKey || !vapidPrivateKey || !vapidSubject) {
  logger.error('Error: VAPID_PUBLIC_KEY, VAPID_PRIVATE_KEY, and VAPID_SUBJECT must be set in the environment variables.');
  process.exit(1);
}

// --- Web Push Setup ---
webpush.setVapidDetails(
  vapidSubject,
  vapidPublicKey,
  vapidPrivateKey
);

// Configure DNS settings for more reliable resolution in containerized environments
// These settings can help with temporary DNS resolution failures
dns.setDefaultResultOrder('ipv4first'); // Prefer IPv4 to avoid some IPv6 issues in containers
const dnsTimeout = parseInt(process.env.DNS_TIMEOUT_MS || 5000, 10);
dns.setServers(dns.getServers()); // Reset DNS servers (can help in some Docker environments)

// You can optionally configure a specific DNS server if needed:
// Example: dns.setServers(['8.8.8.8', '1.1.1.1']);

// --- Utility function for retrying web push notifications with exponential backoff ---
async function sendWebPushWithRetry(subscription, payload, retryCount = 0, delay = initialRetryDelay) {
  try {
    return await webpush.sendNotification(subscription, payload);
  } catch (error) {
    // Check if the error is a DNS resolution error that might be temporary
    const isDnsError = error.code === 'EAI_AGAIN' || 
                       error.code === 'ENOTFOUND' || 
                       error.code === 'ETIMEDOUT';
    
    if (isDnsError && retryCount < maxRetries) {
      console.log(`DNS resolution failed (${error.code}). Retrying notification in ${delay}ms (attempt ${retryCount + 1}/${maxRetries})...`);
      
      // Wait for the delay
      await new Promise(resolve => setTimeout(resolve, delay));
      
      // Exponential backoff with jitter
      const nextDelay = delay * (1.5 + Math.random() * 0.5);
      
      // Retry recursively with increased count and delay
      return sendWebPushWithRetry(subscription, payload, retryCount + 1, nextDelay);
    }
    
    // If we've exhausted retries or it's not a DNS error, rethrow
    throw error;
  }
}

// --- Subscription Loading and Management ---
let subscriptions = {}; // In-memory cache of subscriptions

function loadSubscriptions() {
    if (!fs.existsSync(subscriptionsFilePath)) {
        logger.warn(`Warning: Subscriptions file not found at ${subscriptionsFilePath}. Creating an empty file.`);
        try {
            fs.writeFileSync(subscriptionsFilePath, '{}', 'utf8');
            subscriptions = {};
        } catch (err) {
            logger.error(`Error: Could not create subscriptions file at ${subscriptionsFilePath}.`, err);
            // Exit or continue with empty object depending on desired robustness
             process.exit(1); // Exit if we can't even create the file
        }
    } else {
        try {
            const data = fs.readFileSync(subscriptionsFilePath, 'utf8');
            subscriptions = JSON.parse(data || '{}'); // Handle empty file case
            logger.info(`Loaded ${Object.keys(subscriptions).length} subscriptions from ${subscriptionsFilePath}`);
        } catch (err) {
            logger.error(`Error reading or parsing subscriptions file at ${subscriptionsFilePath}. Please ensure it's valid JSON. Using empty cache.`, err);
            // Continue with empty subscriptions, but log the error
            subscriptions = {};
        }
    }
}

function saveSubscriptions() {
    try {
        fs.writeFileSync(subscriptionsFilePath, JSON.stringify(subscriptions, null, 2), 'utf8'); // Pretty print JSON
        logger.info(`Subscriptions successfully saved to ${subscriptionsFilePath}`);
    } catch (err) {
        logger.error(`Error writing subscriptions file: ${subscriptionsFilePath}`, err);
        // Note: The in-memory object is updated, but persistence failed.
    }
}

// Initial load
loadSubscriptions();


// --- Express App Setup ---
const app = express();

// --- CORS Middleware ---
const corsOptions = {
  origin: (origin, callback) => {
    if (!origin || allowedOrigins.length === 0 || allowedOrigins.includes(origin)) {
      callback(null, true);
    } else {
      console.warn(`CORS: Blocked origin: ${origin}`);
      callback(new Error('Not allowed by CORS'));
    }
  },
  methods: allowedMethods,
  allowedHeaders: allowedHeaders,
  optionsSuccessStatus: 204 // For pre-flight requests
};
app.use(cors(corsOptions));
// Enable pre-flight requests for all relevant routes
app.options('/webhook', cors(corsOptions));
app.options('/subscribe', cors(corsOptions));


// --- Body Parsing Middleware ---
app.use(express.json());

// --- Basic Authentication Middleware ---
const authenticateBasic = (req, res, next) => {
  // Skip authentication for OPTIONS requests (CORS preflight)
  if (req.method === 'OPTIONS') {
    return next();
  }

  // Skip authentication if username or password are not set in environment
  if (!basicAuthUsername || !basicAuthPassword) {
    logger.warn('Auth: Basic Auth username or password not configured. Skipping authentication.');
    return next();
  }

  const authHeader = req.headers.authorization;

  if (!authHeader || !authHeader.startsWith('Basic ')) {
    logger.warn('Auth: Missing or malformed Basic Authorization header');
    res.setHeader('WWW-Authenticate', 'Basic realm="Restricted Area"');
    return res.status(401).json({ message: 'Unauthorized: Basic Authentication required' });
  }

  const credentials = authHeader.split(' ')[1];
  const decodedCredentials = Buffer.from(credentials, 'base64').toString('utf8');
  const [username, password] = decodedCredentials.split(':');

  // Note: Use constant-time comparison for production environments if possible,
  // but for this scope, direct comparison is acceptable.
  if (username === basicAuthUsername && password === basicAuthPassword) {
    logger.debug('Auth: Basic Authentication successful.');
    return next();
  } else {
    logger.warn('Auth: Invalid Basic Authentication credentials received.');
    res.setHeader('WWW-Authenticate', 'Basic realm="Restricted Area"');
    return res.status(401).json({ message: 'Unauthorized: Invalid credentials' });
  }
};

// --- Routes ---

// Subscribe endpoint: Add a new button->subscription mapping
// Apply Basic Authentication
app.post('/subscribe', authenticateBasic, async (req, res) => {
    const { button_id, subscription } = req.body;
    
    logger.debug('All headers received:');
    Object.keys(req.headers).forEach(headerName => {
      logger.debug(`  ${headerName}: ${req.headers[headerName]}`);
    });

    logger.info(`Received subscription request for button: ${button_id}`);

    // Basic Validation
    if (!button_id || typeof button_id !== 'string' || button_id.trim() === '') {
        logger.warn('Subscription Error: Missing or invalid button_id');
        return res.status(400).json({ message: 'Bad Request: Missing or invalid button_id' });
    }
    if (!subscription || typeof subscription !== 'object' || !subscription.endpoint || !subscription.keys || !subscription.keys.p256dh || !subscription.keys.auth) {
        logger.warn('Subscription Error: Missing or invalid subscription object structure');
        return res.status(400).json({ message: 'Bad Request: Missing or invalid subscription object' });
    }

    const normalizedButtonId = button_id.toLowerCase(); // Use lowercase for consistency

    // Update in-memory store
    subscriptions[normalizedButtonId] = subscription;
    logger.info(`Subscription for button ${normalizedButtonId} added/updated in memory.`);

    // Persist to file
    try {
        saveSubscriptions(); // Call the save function
        res.status(201).json({ message: `Subscription saved successfully for button ${normalizedButtonId}` });
    } catch (err) // Catch potential synchronous errors from saveSubscriptions (though unlikely with writeFileSync)
    {
        // saveSubscriptions already logs the error, but we send a 500 response
        res.status(500).json({ message: 'Internal Server Error: Failed to save subscription to file' });
    }
});

// --- Flic Webhook Endpoint (GET only) ---
// Apply Basic Authentication
app.get('/webhook/:click_type', authenticateBasic, async (req, res) => {
  // Get buttonName from Header 'Button-Name' and timestamp from Header 'Timestamp'
  const buttonName = req.headers['button-name'];
  const timestamp = req.headers['timestamp'];
  // Get click_type from URL path
  const click_type = req.params.click_type;
  // Get battery level from Header 'Button-Battery-Level'
  const batteryLevelHeader = req.headers['button-battery-level'];
  // Use 'N/A' if header is missing or empty, otherwise parse as integer (or keep as string if parsing fails)
  const batteryLevel = batteryLevelHeader ? parseInt(batteryLevelHeader, 10) || batteryLevelHeader : 'N/A';

  // Log all headers received from Flic
  logger.debug('All headers received:');
  Object.keys(req.headers).forEach(headerName => {
    logger.debug(`  ${headerName}: ${req.headers[headerName]}`);
  });

  logger.info(`Received GET webhook: Button=${buttonName}, Type=${click_type}, Timestamp=${timestamp || 'N/A'}`);

  // Basic validation
  if (!buttonName || !click_type) {
    logger.warn(`Webhook Error: Missing Button-Name header or click_type query parameter`);
    return res.status(400).json({ message: 'Bad Request: Missing Button-Name header or click_type query parameter' });
  }

  const normalizedButtonName = buttonName.toLowerCase(); // Use lowercase for lookup consistency

  // Find the subscription associated with this normalized button name
  const subscription = subscriptions[normalizedButtonName];

  if (!subscription) {
    logger.warn(`Webhook: No subscription found for button ID: ${normalizedButtonName} (original: ${buttonName})`);
    return res.status(404).json({ message: `Not Found: No subscription configured for button ${normalizedButtonName}` });
  }

  // --- Send Web Push Notification ---
  const payload = JSON.stringify({
    title: 'Flic Button Action',
    body: `Button ${normalizedButtonName}: ${click_type}`, // Simplified body
    data: {
        action: click_type,
        button: normalizedButtonName, // Send normalized button name
        timestamp: timestamp || new Date().toISOString(),
        batteryLevel: batteryLevel // Use the extracted value
    }
    // icon: '/path/to/icon.png'
  });

  try {
    logger.debug(`Subscription endpoint: ${subscription.endpoint}`);
    logger.info(`Sending push notification for ${normalizedButtonName} to endpoint: ${subscription.endpoint.substring(0, 40)}...`);
    await sendWebPushWithRetry(subscription, payload);
    logger.info(`Push notification sent successfully for button ${normalizedButtonName}.`);
    res.status(200).json({ message: 'Push notification sent successfully' });
  } catch (error) {
    logger.error(`Error sending push notification for button ${normalizedButtonName}:`, error.body || error.message || error);

    if (error.statusCode === 404 || error.statusCode === 410) {
      logger.warn(`Subscription for button ${normalizedButtonName} is invalid or expired (404/410). Removing it.`);
      // Optionally remove the stale subscription
      delete subscriptions[normalizedButtonName];
      saveSubscriptions(); // Attempt to save the updated list
      res.status(410).json({ message: 'Subscription Gone' });
    } else {
      res.status(500).json({ message: 'Internal Server Error: Failed to send push notification' });
    }
  }
});

// --- Start Server ---
// Use http.createServer to allow graceful shutdown
const server = http.createServer(app);

server.listen(port, () => {
  logger.info(`Flic Webhook to WebPush server listening on port ${port}`);
  logger.info(`Allowed Origins: ${allowedOrigins.length > 0 ? allowedOrigins.join(', ') : '(Any)'}`);
  logger.info(`Allowed Methods: ${allowedMethods.join(', ')}`);
  logger.info(`Allowed Headers: ${allowedHeaders.join(', ')}`);
  // Log Basic Auth status instead of Flic Secret
  if (basicAuthUsername && basicAuthPassword) {
    logger.info('Authentication: Basic Auth Enabled');
  } else {
    logger.info('Authentication: Basic Auth Disabled (username/password not set)');
  }
  logger.info(`Subscription Endpoint Auth: ${basicAuthUsername && basicAuthPassword ? 'Enabled (Basic)' : 'Disabled'}`);
  logger.info(`Subscriptions File: ${subscriptionsFilePath}`);
  logger.info(`Push Notification Retry Config: ${maxRetries} retries, ${initialRetryDelay}ms initial delay`);
  logger.info(`DNS Config: IPv4 first, timeout ${dnsTimeout}ms`);
  logger.info(`HTTP Timeout: ${httpTimeout}ms`);
  logger.info(`Log Level: ${LOG_LEVEL.toUpperCase()}`);
});

// --- Graceful Shutdown ---
const closeGracefully = (signal) => {
    logger.info(`${signal} signal received: closing HTTP server`);
    server.close(() => {
        logger.info('HTTP server closed');
        // Perform any other cleanup here if needed
        process.exit(0);
    });

    // Force close server after 10 seconds
    setTimeout(() => {
        logger.error('Could not close connections in time, forcefully shutting down');
        process.exit(1);
    }, 10000); // 10 seconds timeout - This is a literal so no need to parse
}

process.on('SIGTERM', () => closeGracefully('SIGTERM'));
process.on('SIGINT', () => closeGracefully('SIGINT')); // Handle Ctrl+C