fix(kilo-pass): prevent duplicate checkout sessions

apps/web/src/lib/kilo-pass/checkout-session.ts

@@ -0,0 +1,111 @@
+import { db } from '@/lib/drizzle';
+import { getKiloPassStateForUser } from '@/lib/kilo-pass/state';
+import { isStripeSubscriptionEnded } from '@/lib/kilo-pass/stripe-subscription-status';
+import { client as stripe } from '@/lib/stripe-client';
+import { TRPCError } from '@trpc/server';
+import { sql } from 'drizzle-orm';
+import type Stripe from 'stripe';
+
+type CreateOrReuseKiloPassCheckoutSessionParams = {
+  userId: string;
+  stripeCustomerId: string;
+  metadata: Stripe.MetadataParam;
+  createSession: () => Promise<Stripe.Checkout.Session>;
+};
+
+const STRIPE_CHECKOUT_TIMEOUT_MS = 10_000;
+const MAX_STRIPE_PAGES = 3;
+const PRODUCT_METADATA_KEYS = [
+  'tier',
+  'cadence',
+  'kiloclawHostingPlan',
+  'kiloclawInstanceId',
+  'kiloclawPriceVersion',
+] as const;
+
+export async function createOrReuseKiloPassCheckoutSession(
+  params: CreateOrReuseKiloPassCheckoutSessionParams
+): Promise<{ url: string | null }> {
+  return db.transaction(async tx => {
+    await tx.execute(
+      sql`SELECT pg_advisory_xact_lock(hashtextextended(${`kilo-pass:checkout:${params.userId}`}, 0))`
+    );
+
+    const existing = await getKiloPassStateForUser(tx, params.userId);
+    if (existing && !isStripeSubscriptionEnded(existing.status)) {
+      throw new TRPCError({
+        code: 'BAD_REQUEST',
+        message: 'You already have an active Kilo Pass subscription.',
+      });
+    }
+
+    const isUserKiloPassSession = (session: Stripe.Checkout.Session) =>
+      session.metadata?.type === 'kilo-pass' && session.metadata.kiloUserId === params.userId;
+    const matchesRequestedProduct = (session: Stripe.Checkout.Session) =>
+      PRODUCT_METADATA_KEYS.every(key => session.metadata?.[key] === params.metadata[key]);
+    let checkoutCursor: string | undefined;
+    let checkoutPageCount = 0;
+    do {
+      const openSessions = await stripe.checkout.sessions.list(
+        {
+          customer: params.stripeCustomerId,
+          status: 'open',
+          limit: 100,
+          ...(checkoutCursor ? { starting_after: checkoutCursor } : {}),
+        },
+        { timeout: STRIPE_CHECKOUT_TIMEOUT_MS }
+      );
+      checkoutPageCount++;
+      for (const session of openSessions.data.filter(isUserKiloPassSession)) {
+        if (matchesRequestedProduct(session) && typeof session.url === 'string') {
+          return { url: session.url };
+        }
+        await stripe.checkout.sessions.expire(session.id, {
+          timeout: STRIPE_CHECKOUT_TIMEOUT_MS,
+        });
+      }
+      checkoutCursor =
+        openSessions.has_more && checkoutPageCount < MAX_STRIPE_PAGES
+          ? openSessions.data.at(-1)?.id
+          : undefined;
+    } while (checkoutCursor);
+
+    let subscriptionCursor: string | undefined;
+    let hasLiveStripeSubscription = false;
+    let subscriptionPageCount = 0;
+    do {
+      const subscriptions = await stripe.subscriptions.list(
+        {
+          customer: params.stripeCustomerId,
+          status: 'all',
+          limit: 100,
+          ...(subscriptionCursor ? { starting_after: subscriptionCursor } : {}),
+        },
+        { timeout: STRIPE_CHECKOUT_TIMEOUT_MS }
+      );
+      subscriptionPageCount++;
+      hasLiveStripeSubscription = subscriptions.data.some(
+        subscription =>
+          subscription.metadata.type === 'kilo-pass' &&
+          subscription.metadata.kiloUserId === params.userId &&
+          !isStripeSubscriptionEnded(subscription.status)
+      );
+      subscriptionCursor =
+        !hasLiveStripeSubscription &&
+        subscriptions.has_more &&
+        subscriptionPageCount < MAX_STRIPE_PAGES
+          ? subscriptions.data.at(-1)?.id
+          : undefined;
+    } while (subscriptionCursor);
+
+    if (hasLiveStripeSubscription) {
+      throw new TRPCError({
+        code: 'BAD_REQUEST',
+        message: 'You already have an active Kilo Pass subscription.',
+      });
+    }
+
+    const session = await params.createSession();
+    return { url: typeof session.url === 'string' ? session.url : null };
+  });
+}