const express = require('express');
const cors = require('cors');
const admin = require('firebase-admin');

const app = express();
const PORT = process.env.PORT || 7860;

app.use(cors());
app.use(express.json());

// ==========================================
// ০. ফায়ারবেস এডমিন এসডিকে (Hugging Face Secrets থেকে)
// ==========================================
try {
  // Hugging Face Secrets থেকে স্ট্রিংটি নেওয়া হচ্ছে
  const secretKeyString = process.env.FIREBASE_SERVICE_ACCOUNT;

  if (!secretKeyString) {
    throw new Error("FIREBASE_SERVICE_ACCOUNT secret is missing in Hugging Face Spaces settings!");
  }

  // স্ট্রিংটিকে JSON অবজেক্টে রূপান্তর করা
  const serviceAccount = JSON.parse(secretKeyString);

  admin.initializeApp({
    credential: admin.credential.cert(serviceAccount)
  });
  
  console.log("Firebase Admin SDK initialized successfully using Hugging Face Secrets!");
} catch (error) {
  console.error("Firebase Initialization Failed:", error.message);
  process.exit(1); // সিক্রেট না থাকলে সার্ভার রান করবে না
}

// ==========================================
// ১. হেলথ চেক রাউট (/health এবং /check)
// ==========================================
const healthCheckHandler = (req, res) => {
  res.status(200).send('ok');
};

app.all('/health', healthCheckHandler);
app.all('/check', healthCheckHandler);

// ==========================================
// ২. সিকিউরিটি মিডলওয়্যার (Middleware)
// ==========================================
const enforcePostOnly = (req, res, next) => {
  if (req.method !== 'POST') {
    return res.status(405).json({ 
      success: false, 
      message: `Method ${req.method} Not Allowed. Only POST requests are accepted on this endpoint.` 
    });
  }
  next();
};

// ==========================================
// ৩. মূল কার্যকারী রাউট (/subscribe এবং /unsubscribe)
// ==========================================

// --- সাবস্ক্রাইব সেকশন ---
app.post('/subscribe', enforcePostOnly, async (req, res) => {
  const { fcm_token, selected_category, action } = req.body;

  if (!fcm_token || !selected_category || action !== 'subscribe') {
    return res.status(400).json({ success: false, message: "Invalid payload or wrong action for subscription." });
  }

  try {
    await admin.messaging().subscribeToTopic(fcm_token, selected_category);
    console.log(`Successfully subscribed token to topic: ${selected_category}`);
    
    res.status(200).json({ 
      success: true, 
      message: `Successfully registered to ${selected_category} category.` 
    });
  } catch (error) {
    console.error("Firebase subscription error:", error);
    res.status(500).json({ success: false, error: error.message });
  }
});

// --- আন-সাবস্ক্রাইব সেকশন ---
app.post('/unsubscribe', enforcePostOnly, async (req, res) => {
  const { fcm_token, selected_category, action } = req.body;

  if (!fcm_token || !selected_category || action !== 'unsubscribe') {
    return res.status(400).json({ success: false, message: "Invalid payload or wrong action for unsubscription." });
  }

  try {
    await admin.messaging().unsubscribeFromTopic(fcm_token, selected_category);
    console.log(`Successfully unsubscribed token from topic: ${selected_category}`);

    res.status(200).json({ 
      success: true, 
      message: `Successfully removed from ${selected_category} category.` 
    });
  } catch (error) {
    console.error("Firebase unsubscription error:", error);
    res.status(500).json({ success: false, error: error.message });
  }
});

// ==========================================
// ৪. গ্লোবাল ক্যাচ-অল রাউট
// ==========================================
app.use((req, res) => {
  res.status(404).json({ success: false, message: "Endpoint not found." });
});

app.listen(PORT, '0.0.0.0', () => {
  console.log(`Server is running on port ${PORT}`);
});