const express = require('express');
const webpush = require('web-push');
const cors = require('cors');
const fs = require('fs');
const path = require('path');

// 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');
const flicSecret = process.env.FLIC_SECRET; // Optional Bearer token secret for Flic webhook
// 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);


// --- Validation ---
if (!vapidPublicKey || !vapidPrivateKey || !vapidSubject) {
  console.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
);

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

function loadSubscriptions() {
    if (!fs.existsSync(subscriptionsFilePath)) {
        console.warn(`Warning: Subscriptions file not found at ${subscriptionsFilePath}. Creating an empty file.`);
        try {
            fs.writeFileSync(subscriptionsFilePath, '{}', 'utf8');
            subscriptions = {};
        } catch (err) {
            console.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
            console.log(`Loaded ${Object.keys(subscriptions).length} subscriptions from ${subscriptionsFilePath}`);
        } catch (err) {
            console.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
        console.log(`Subscriptions successfully saved to ${subscriptionsFilePath}`);
    } catch (err) {
        console.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('/flic-webhook', cors(corsOptions));
app.options('/subscribe', cors(corsOptions));


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

// --- Authentication Middleware (For Flic Webhook Only) ---
const authenticateFlicRequest = (req, res, next) => {
  // Only apply auth if flicSecret is configured
  if (!flicSecret) {
    return next();
  }

  const authHeader = req.headers.authorization;
  if (!authHeader || !authHeader.startsWith('Bearer ')) {
    console.warn('Auth (Flic): Missing or malformed Authorization header');
    return res.status(401).json({ message: 'Unauthorized: Missing or malformed Bearer token' });
  }

  const token = authHeader.split(' ')[1];
  if (token !== flicSecret) {
    console.warn('Auth (Flic): Invalid Bearer token received');
    return res.status(401).json({ message: 'Unauthorized: Invalid token' });
  }

  console.log('Auth (Flic): Request authenticated successfully.');
  next();
};

app.post('/subscribe', async (req, res) => {
    const { button_id, subscription } = req.body;

    console.log(`Received subscription request for button: ${button_id}`);

    // Basic Validation
    if (!button_id || typeof button_id !== 'string' || button_id.trim() === '') {
        console.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) {
        console.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;
    console.log(`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 ---
// Apply Flic-specific authentication ONLY to this route
app.post('/flic-webhook', authenticateFlicRequest, async (req, res) => {
  // Assuming Flic sends 'button_id' which is the serial number
  const { button_id, click_type, timestamp } = req.body;

  console.log(`Received webhook: Button=${button_id}, Type=${click_type}, Timestamp=${timestamp || 'N/A'}`);

  // Basic validation
  if (!button_id || !click_type) {
    console.warn(`Webhook Error: Missing button_id or click_type`);
    return res.status(400).json({ message: 'Bad Request: Missing button_id or click_type' });
  }

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

  // Find the subscription associated with this button ID
  const subscription = subscriptions[normalizedButtonId];

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

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

  try {
    console.log(`Sending push notification for ${normalizedButtonId} to endpoint: ${subscription.endpoint.substring(0, 40)}...`);
    await webpush.sendNotification(subscription, payload);
    console.log(`Push notification sent successfully for button ${normalizedButtonId}.`);
    res.status(200).json({ message: 'Push notification sent successfully' });
  } catch (error) {
    console.error(`Error sending push notification for button ${normalizedButtonId}:`, error.body || error.message || error);

    if (error.statusCode === 404 || error.statusCode === 410) {
      console.warn(`Subscription for button ${normalizedButtonId} is invalid or expired (404/410). Removing it.`);
      // Optionally remove the stale subscription
      delete subscriptions[normalizedButtonId];
      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' });
    }
  }
});

// --- Health Check Endpoint ---
app.get('/health', (req, res) => {
  res.status(200).json({
      status: 'UP',
      timestamp: new Date().toISOString(),
      subscription_count: Object.keys(subscriptions).length
    });
});

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

server.listen(port, () => {
  console.log(`Flic Webhook to WebPush server listening on port ${port}`);
  console.log(`Allowed Origins: ${allowedOrigins.length > 0 ? allowedOrigins.join(', ') : '(Any)'}`);
  console.log(`Allowed Methods: ${allowedMethods.join(', ')}`);
  console.log(`Allowed Headers: ${allowedHeaders.join(', ')}`);
  console.log(`Flic Webhook Auth: ${flicSecret ? 'Enabled (Bearer Token)' : 'Disabled'}`);
  console.log(`Subscription Endpoint Auth: Disabled`);
  console.log(`Subscriptions File: ${subscriptionsFilePath}`);
});

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

    // Force close server after 10 seconds
    setTimeout(() => {
        console.error('Could not close connections in time, forcefully shutting down');
        process.exit(1);
    }, 10000); // 10 seconds timeout
}

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