// paystack-webhook.js
// Node >= 14, install dependencies:
// npm install express firebase-admin

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

const app = express();

// -------------------------------------------------
// Environment variables (set these in your env/secrets)
// -------------------------------------------------
// - FIREBASE_CREDENTIALS: stringified JSON service account
// - PAYSTACK_SECRET: your Paystack webhook secret
// - PORT (optional)
// -------------------------------------------------

const {
  FIREBASE_CREDENTIALS,
  PAYSTACK_DEMO_SECRET,
  PAYSTACK_LIVE_SECRET,
  PORT, 
} = process.env;

const PAYSTACK_SECRET = PAYSTACK_DEMO_SECRET; // PAYSTACK_LIVE_SECRET

if (!PAYSTACK_SECRET) {
  console.warn('WARNING: PAYSTACK_SECRET is not set. Webhook signature verification will fail.');
}

// Initialize Firebase Admin using credentials read from env
if (FIREBASE_CREDENTIALS) {
  try {
    const serviceAccount = JSON.parse(FIREBASE_CREDENTIALS);
    admin.initializeApp({
      credential: admin.credential.cert(serviceAccount),
    });
    console.log('Firebase admin initialized from FIREBASE_CREDENTIALS env var.');
  } catch (err) {
    console.error('Failed to parse FIREBASE_CREDENTIALS JSON:', err);
    process.exit(1);
  }
} else {
  console.warn('FIREBASE_CREDENTIALS not provided. Firebase admin not initialized.');
}

// Important: use raw body parser to verify Paystack signature.
// Paystack signs the raw request body (HMAC SHA512) and puts signature in header `x-paystack-signature`
app.use(
  express.raw({
    type: 'application/json',
    limit: '1mb',
  })
);

// Utility: verify x-paystack-signature
function verifyPaystackSignature(rawBodyBuffer, signatureHeader) {
  if (!PAYSTACK_SECRET) return false;
  const hmac = crypto.createHmac('sha512', PAYSTACK_SECRET);
  hmac.update(rawBodyBuffer);
  const expected = hmac.digest('hex');
  // Paystack header is hex string; compare in constant-time
  return crypto.timingSafeEqual(Buffer.from(expected, 'utf8'), Buffer.from(signatureHeader || '', 'utf8'));
}

// Helper: safe JSON parse
function safeParseJSON(raw) {
  try {
    return JSON.parse(raw);
  } catch (err) {
    return null;
  }
}

// Webhook endpoint
app.post('/webhook/paystack', (req, res) => {
  const raw = req.body; // Buffer because we used express.raw
  const signature = req.get('x-paystack-signature') || req.get('X-Paystack-Signature');

  // Verify signature
  if (!signature || !verifyPaystackSignature(raw, signature)) {
    console.warn('Paystack webhook signature verification failed. Signature header:', signature);
    // Respond 400 to indicate invalid signature
    return res.status(400).json({ ok: false, message: 'Invalid signature' });
  }

  // Parse payload
  const bodyStr = raw.toString('utf8');
  const payload = safeParseJSON(bodyStr);

  if (!payload) {
    console.warn('Could not parse webhook JSON payload.');
    return res.status(400).json({ ok: false, message: 'Invalid JSON' });
  }

  // Paystack typically uses an "event" field: e.g. "charge.success", "refund.create", ...
  const event = (payload.event || payload.type || '').toString();

  // Identify refund events and payment events (first-time or recurring)
  const isRefund = /refund/i.test(event); // matches refund.* etc.
  const isChargeSuccess = /charge\.success/i.test(event); // common payment event
  // add some broad matches for invoice/subscription events that might indicate recurring payments
  const isInvoiceOrSubscription = /invoice\.(payment_succeeded|paid)|subscription\./i.test(event);

  const isPayment = isChargeSuccess || isInvoiceOrSubscription;

  // Only interested in refunds and payments
  if (isRefund || isPayment) {
    console.log('--- PAYSTACK WEBHOOK (INTERESTING EVENT) ---');
    console.log('event:', event);
    console.log('payload:', JSON.stringify(payload, null, 2));

    // TODO: add your business logic here:
    // - update Firestore / user subscription state
    // - create refund records, notify user, retry flows, etc.
    // Example (pseudo):
    // const db = admin.firestore();
    // await db.collection('paystack-webhooks').add({ receivedAt: admin.firestore.FieldValue.serverTimestamp(), event, payload });

    // If you want to persist the webhook to Firestore for auditing, uncomment above and ensure Firebase is initialized
  } else {
    // For debugging, you can log minimal info for non-interesting events
    console.log(`Received Paystack webhook for event "${event}" — ignored (not refund/payment).`);
  }

  // Acknowledge the webhook promptly with 200 OK so Paystack stops retrying
  return res.status(200).json({ ok: true });
});

// Simple health check
app.get('/health', (_req, res) => res.json({ ok: true }));

app.listen(PORT, () => {
  console.log(`Paystack webhook server listening on port ${PORT}`);
  console.log('POST /webhook/paystack to receive Paystack callbacks');
});