Building WhatsApp AI Sales & FAQ Bots: Meta Cloud API, Webhooks & Automated Product Catalogs

import express from 'express';
import crypto from 'crypto';

const router = express.Router();

// 1. Meta Webhook Verification Challenge
router.get('/webhook', (req, res) => {
  const mode = req.query['hub.mode'];
  const token = req.query['hub.verify_token'];
  const challenge = req.query['hub.challenge'];

  if (mode === 'subscribe' && token === process.env.META_VERIFY_TOKEN) {
    return res.status(200).send(challenge);
  }
  return res.sendStatus(403);
});

// 2. Incoming Messages Webhook
router.post('/webhook', express.raw({ type: 'application/json' }), async (req, res) => {
  const signature = req.headers['x-hub-signature-256'] as string;
  const hmac = crypto.createHmac('sha256', process.env.META_APP_SECRET!);
  const digest = 'sha256=' + hmac.update(req.body).digest('hex');

  if (signature !== digest) {
    return res.status(401).send('Invalid signature');
  }

  // Acknowledge Meta immediately within 500ms
  res.sendStatus(200);

  const payload = JSON.parse(req.body.toString());
  // Offload to BullMQ worker for LLM inference & catalog lookup
  await messageQueue.add('process_whatsapp_msg', payload);
});