NestJS SaaS
starter

// billing.service.ts — verify the webhook is authentic
try {
  event = this.dodo.webhooks.unwrap(payload, { headers });
} catch (err) {
  const message = err instanceof Error ? err.message : "Unknown error";
  this.logger.error(`Webhook signature verification failed: ${message}`);
  throw new BadRequestException("Invalid webhook signature");
}

// Duplicate webhook? Skip silently — no double charges
const existing = await this.prisma.webhookEvent.findUnique({
  where: { eventId: webhookId },
});

if (existing) {
  this.logger.log(`Webhook event ${webhookId} already processed, skipping`);
  return { received: true };
}

await this.prisma.purchase.create({
  data: {
    userId,
    paymentId,
    amount,
    currency,
    status: "completed",
  },
});

// Non-blocking — payment is already recorded
this.emailService
  .sendPurchaseConfirmation(
    user.email, user.name ?? user.email, amountFormatted
  )
  .catch((err: unknown) =>
    this.logger.error("Failed to send purchase confirmation", err)
  );

// Mark processed — future duplicates will hit the idempotency guard
await this.prisma.webhookEvent.create({
  data: {
    eventId: webhookId,
    type: eventType,
  },
});

return { received: true };

it("should skip if webhook already processed (idempotency)", async () => {
  prisma.webhookEvent.findUnique.mockResolvedValue({
    id: "wh-1", eventId: "wh_test_123",
    type: "payment.succeeded", processedAt: new Date(),
  });

  const result = await service.handleWebhookEvent("payload", headers);

  expect(result).toEqual({ received: true });
  expect(prisma.purchase.create).not.toHaveBeenCalled();
});