Initial OSS scaffold from Songs2VID (pre-strip)

lib/stripe-checkout.ts

@@ -0,0 +1,71 @@
+import type Stripe from "stripe";
+import { STRIPE_PRODUCT_TAX_CODE } from "@/lib/credits";
+import { prisma } from "@/lib/db";
+import { getStripe } from "@/lib/stripe";
+
+/** Enable Stripe Tax only when Dashboard registrations are active (STRIPE_AUTOMATIC_TAX=true). */
+export function isStripeAutomaticTaxEnabled(): boolean {
+  return process.env.STRIPE_AUTOMATIC_TAX === "true";
+}
+
+/**
+ * Shared Checkout Session options required/recommended by Stripe for SaaS:
+ * - client_reference_id for linking
+ * - automatic_tax (opt-in) + customer_update.address when tax is on
+ * - tax_code already set on product_data by callers
+ */
+export function checkoutTaxAndReferenceOptions(userId: string): Partial<Stripe.Checkout.SessionCreateParams> {
+  const opts: Partial<Stripe.Checkout.SessionCreateParams> = {
+    client_reference_id: userId,
+  };
+
+  if (isStripeAutomaticTaxEnabled()) {
+    opts.automatic_tax = { enabled: true };
+    opts.customer_update = { address: "auto", name: "auto" };
+    // Collect billing address so tax can be calculated for new/returning customers
+    opts.billing_address_collection = "required";
+  }
+
+  return opts;
+}
+
+/** tax_behavior required on Prices when automatic tax is enabled. */
+export function priceDataTaxFields(): { tax_behavior?: Stripe.Checkout.SessionCreateParams.LineItem.PriceData["tax_behavior"] } {
+  if (!isStripeAutomaticTaxEnabled()) return {};
+  // Exclusive: listed prices are pre-tax; VAT/GST added at checkout
+  return { tax_behavior: "exclusive" };
+}
+
+export function productDataWithTaxCode(
+  name: string,
+  description: string,
+): Stripe.Checkout.SessionCreateParams.LineItem.PriceData.ProductData {
+  return {
+    name,
+    description,
+    tax_code: STRIPE_PRODUCT_TAX_CODE,
+  };
+}
+
+/** Ensure the app user has a Stripe Customer and return its id. */
+export async function ensureStripeCustomer(userId: string, email: string): Promise<string> {
+  const dbUser = await prisma.user.findUniqueOrThrow({
+    where: { id: userId },
+    select: { stripeCustomerId: true },
+  });
+
+  if (dbUser.stripeCustomerId) return dbUser.stripeCustomerId;
+
+  const stripe = getStripe();
+  const customer = await stripe.customers.create({
+    email,
+    metadata: { userId },
+  });
+
+  await prisma.user.update({
+    where: { id: userId },
+    data: { stripeCustomerId: customer.id },
+  });
+
+  return customer.id;
+}