Stripe Custom Connect Split-Payout Engine

import Stripe from 'stripe';
import { Request, Response } from 'express';
import Redis from 'ioredis';

const stripe = new Stripe(process.env.STRIPE_SECRET_KEY!, { apiVersion: '2024-06-20' });
const redis = new Redis(process.env.REDIS_URL!);

export async function handleStripeWebhook(req: Request, res: Response) {
  const sig = req.headers['stripe-signature'] as string;
  let event: Stripe.Event;

  try {
    // 1. MUST use raw buffer body for signature check
    event = stripe.webhooks.constructEvent(req.body, sig, process.env.STRIPE_WEBHOOK_SECRET!);
  } catch (err: any) {
    console.error(`[Stripe Signature Error] ${err.message}`);
    return res.status(400).send(`Webhook Signature Verification Failed`);
  }

  // 2. Distributed Idempotency Lock (60-second TTL prevents concurrent execution)
  const lockKey = `stripe:lock:${event.id}`;
  const acquired = await redis.set(lockKey, 'locked', 'EX', 60, 'NX');
  if (!acquired) {
    console.warn(`[Stripe Duplicate Event] ${event.id} currently processing or processed.`);
    return res.status(200).json({ received: true, deduplicated: true });
  }

  try {
    switch (event.type) {
      case 'invoice.payment_succeeded':
        const invoice = event.data.object as Stripe.Invoice;
        await fulfillSubscription(invoice.subscription as string, invoice.customer as string);
        break;
      case 'customer.subscription.deleted':
        await revokeEntitlements(event.data.object.id);
        break;
    }

    // Mark permanently processed (24-hour expiration)
    await redis.set(`stripe:processed:${event.id}`, 'done', 'EX', 86400);
    return res.status(200).json({ success: true });
  } catch (procErr) {
    console.error(`[Stripe Fulfillment Failed] Event ${event.id}:`, procErr);
    // Release lock on error so safe Stripe retries can re-attempt
    await redis.del(lockKey);
    return res.status(500).send('Internal Processing Failure');
  }
}