podcastdistributiona/lib/billing/webhooks/stripe.ts

import type Stripe from "stripe";
import { stripe } from "../stripe";
import { upsertSubscription } from "../subscription";
import { planFromStripePrice } from "../catalog";
import { PLAN_ORDER, type PlanKey } from "../plans";

/** Narrow attacker-influenceable metadata to a known PlanKey, else null. */
function planFromMetadata(value?: string | null): PlanKey | null {
  return value && (PLAN_ORDER as string[]).includes(value) ? (value as PlanKey) : null;
}

function normalizeStatus(status: Stripe.Subscription.Status): string {
  switch (status) {
    case "active":
    case "trialing":
    case "past_due":
    case "paused":
      return status;
    default:
      return "canceled"; // canceled | incomplete | incomplete_expired | unpaid
  }
}

async function syncStripeSubscription(
  sub: Stripe.Subscription,
  metadata?: Stripe.Metadata | null
) {
  const item = sub.items.data[0];
  const priceId = item?.price?.id;
  const mapped = priceId ? planFromStripePrice(priceId) : null;
  // metadata.plan is attacker-influenceable; only honour it if it's a known plan.
  // The price-mapping fallback (derived from the real Stripe price) is preferred.
  const plan: PlanKey = planFromMetadata(metadata?.plan) ?? mapped?.plan ?? "free";
  const referenceId = metadata?.subjectId || sub.metadata?.subjectId;
  if (!referenceId || referenceId.trim() === "") {
    console.warn("[stripe] subscription without subjectId metadata, skipping", sub.id);
    return;
  }

  const interval =
    mapped?.interval ?? (item?.price?.recurring?.interval === "year" ? "year" : "month");

  await upsertSubscription({
    provider: "stripe",
    referenceId,
    plan,
    status: normalizeStatus(sub.status),
    billingInterval: interval,
    stripeCustomerId: typeof sub.customer === "string" ? sub.customer : sub.customer.id,
    stripeSubscriptionId: sub.id,
    periodStart: sub.current_period_start ? new Date(sub.current_period_start * 1000) : null,
    periodEnd: sub.current_period_end ? new Date(sub.current_period_end * 1000) : null,
    cancelAtPeriodEnd: sub.cancel_at_period_end,
  });
}

export async function handleStripeEvent(event: Stripe.Event): Promise<void> {
  switch (event.type) {
    case "checkout.session.completed": {
      const session = event.data.object as Stripe.Checkout.Session;
      if (session.mode !== "subscription" || !session.subscription) break;
      const subId =
        typeof session.subscription === "string" ? session.subscription : session.subscription.id;
      const sub = await stripe().subscriptions.retrieve(subId);
      await syncStripeSubscription(sub, session.metadata);
      break;
    }
    case "customer.subscription.created":
    case "customer.subscription.updated":
    case "customer.subscription.deleted": {
      const sub = event.data.object as Stripe.Subscription;
      await syncStripeSubscription(sub, sub.metadata);
      break;
    }
    default:
      break;
  }
}