Payment Provider Router

Payment Provider Router

Concept of the skill

What it is: The typed dispatch layer that sends verified payment events to the correct business handler. Mental model: Verification proves the event is authentic; the router decides what business operation the event represents. Why it exists: Payment events are high-impact and retried by providers, so ambiguous routing can duplicate work or miss fulfillment. What it is NOT: It is not webhook signature verification, subscription database writes, or provider SDK setup. Adjacent concepts: Event type maps, handler isolation, provider abstraction, idempotency. One-line analogy: It is the switchboard that sends a verified payment event to the right desk. Common misconception: Unknown events should return an HTTP error; for Stripe, acknowledging and logging unknown-but-valid events prevents retry storms.

Coverage

• The routing table — a typed dispatch map from Stripe.Event["type"] to handler functions, with a structured "unknown event" fallback that returns 200 (to prevent Stripe retry storms) and logs the unhandled type
• Handler isolation — each handler receives only the specific event subtype it needs (e.g. Stripe.CheckoutSessionCompletedEvent), not the generic Stripe.Event, to avoid casts inside handlers
• Provider abstraction — how to wrap the Stripe-specific router behind a PaymentEvent canonical type so a future provider can be added without changing handler code
• Error surface — handlers must catch their own errors and return a structured result; an uncaught exception must not produce a 500 that triggers Stripe's retry mechanism with an exponential backoff cascade
• Event type coverage audit — which event types are handled, which are known-ignored (acknowledged with a comment), and which are genuinely unknown

Philosophy of the skill

A payment event router has the same discipline requirement as a content source router: prefer an explicit handler over an implicit fallback, surface unhandled events loudly (in logs, not in HTTP status codes — a 400 triggers a retry, a 200 with a log entry does not), and never let one handler own two semantically distinct events. The event type is the authoritative signal for which business operation to perform; ambiguity at this layer produces double-charges, missed provisioning, and unfired dunning emails.

Routing Rules

// lib/payments/router.ts
import Stripe from "stripe";
import { handleCheckoutComplete } from "./handlers/checkout-complete";
import { handlePaymentFailed } from "./handlers/payment-failed";
import { handleSubscriptionDeleted } from "./handlers/subscription-deleted";

type HandlerResult = { ok: boolean; message?: string };

const EVENT_HANDLERS: Partial<
  Record<Stripe.Event["type"], (event: Stripe.Event) => Promise<HandlerResult>>
> = {
  "checkout.session.completed": (e) =>
    handleCheckoutComplete(e as Stripe.CheckoutSessionCompletedEvent),
  "invoice.payment_failed": (e) =>
    handlePaymentFailed(e as Stripe.InvoicePaymentFailedEvent),
  "customer.subscription.deleted": (e) =>
    handleSubscriptionDeleted(e as Stripe.CustomerSubscriptionDeletedEvent),
  // Acknowledged non-actionable events — log and return OK
  "invoice.paid": async () => ({ ok: true, message: "acknowledged" }),
};

export async function routePaymentEvent(event: Stripe.Event): Promise<HandlerResult> {
  const handler = EVENT_HANDLERS[event.type];

  if (!handler) {
    console.warn("[payment-router] unhandled event type", { type: event.type, id: event.id });
    // Return 200 — a 4xx or 5xx would trigger Stripe retry with backoff
    return { ok: true, message: "unhandled_event_type" };
  }

  return handler(event);
}

Routing Decision Rules

Adding a New Event Type

1. Add the Stripe event type string to EVENT_HANDLERS with a typed cast.
2. Write the handler in lib/payments/handlers/<name>.ts — it receives the specific subtype.
3. Add a row to the routing table above documenting what the handler does.
4. If the event should be intentionally ignored, add it to the "acknowledged" row rather than leaving it in the unknown bucket.

Verification

• Every routable event type is in EVENT_HANDLERS with an explicit handler or acknowledgement
• Unknown events return 200 (not 400 or 500) to prevent Stripe retry cascades
• Each handler receives a typed subtype, not the generic Stripe.Event
• Handler errors are caught inside the handler and returned as { ok: false } — they do not propagate to the router
• routePaymentEvent is only called after signature verification (grep for routePaymentEvent — every call site should be downstream of constructEvent)

Do NOT Use When