Phase4: Stripe

src/lib/stripe.ts

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+/**
+ * Server-side Stripe client + helpers for Phase 4 (card payments).
+ *
+ * Architecture (see Phase 4 notes):
+ *   1. Customer clicks "Pay with card" on /billing/<number>.
+ *   2. Server creates Stripe Checkout Session (mode='payment') with
+ *      the invoice total as a single line item. We pass `customer`
+ *      to reuse an existing Stripe Customer if the org already has
+ *      one, otherwise we create one and persist its id in
+ *      org_billing_config.stripe_customer_id.
+ *   3. Returns session.url; the browser redirects there.
+ *   4. Customer pays; Stripe redirects to success_url with the
+ *      session id appended.
+ *   5. /api/stripe/webhook receives `checkout.session.completed`,
+ *      verifies signature, looks up the invoice id from metadata,
+ *      flips the invoice to 'paid'.
+ *
+ * Env vars:
+ *   STRIPE_SECRET_KEY          (required) - sk_test_... in sandbox, sk_live_... in prod
+ *   STRIPE_WEBHOOK_SECRET      (required for webhook) - whsec_...
+ *   APP_BASE_URL               (required) - e.g. https://app.pieced.ch
+ *
+ * SDK: stripe@22.x (Node SDK v22), pinned API version 2026-03-25.dahlia.
+ * Pinning the API version means a `npm update` of the SDK won't
+ * silently change request/response shapes; we explicitly bump when
+ * we want a new API version.
+ */
+
+import Stripe from "stripe";
+import type { Invoice } from "@/types";
+
+// Pinned API version. Bump deliberately, not via dependency update.
+// Keep this matched to the stripe-node major version in package.json.
+const STRIPE_API_VERSION = "2026-03-25.dahlia" as const;
+
+// Cache the client across hot reloads / serverless invocations.
+// We don't instantiate at module load because some build steps run
+// without runtime env vars set — only fail when actually used.
+let cachedClient: Stripe | null = null;
+
+export function getStripeClient(): Stripe {
+  if (cachedClient) return cachedClient;
+  const key = process.env.STRIPE_SECRET_KEY;
+  if (!key) {
+    throw new Error(
+      "STRIPE_SECRET_KEY is not set. Configure it in your environment."
+    );
+  }
+  cachedClient = new Stripe(key, {
+    apiVersion: STRIPE_API_VERSION,
+    // Identify ourselves in Stripe's request logs so support can
+    // distinguish PieCed traffic from other integrations on the
+    // same account.
+    appInfo: {
+      name: "PieCed Portal",
+      version: "1.0.0",
+      url: "https://app.pieced.ch",
+    },
+  });
+  return cachedClient;
+}
+
+/**
+ * Return the configured webhook secret. Separated so the webhook
+ * handler can fail fast with a clear error message rather than the
+ * generic "STRIPE_SECRET_KEY missing" path above.
+ */
+export function getWebhookSecret(): string {
+  const secret = process.env.STRIPE_WEBHOOK_SECRET;
+  if (!secret) {
+    throw new Error(
+      "STRIPE_WEBHOOK_SECRET is not set. Get it from the webhook endpoint in your Stripe dashboard."
+    );
+  }
+  return secret;
+}
+
+/**
+ * Convert a CHF decimal amount (e.g. 123.45) to integer rappen
+ * (e.g. 12345). Stripe API requires integer amounts in the
+ * currency's smallest unit. Centralised so we don't have rounding
+ * drift between callers.
+ */
+export function chfToRappen(amountChf: number): number {
+  // toFixed(2) avoids floating-point ugliness (0.1 + 0.2 = 0.30000000000000004).
+  return Math.round(parseFloat(amountChf.toFixed(2)) * 100);
+}
+
+/**
+ * Look up or create the Stripe Customer for a PieCed org.
+ *
+ * Lazy creation: orgs that only pay by invoice never get a Stripe
+ * Customer. The first "Pay with card" click triggers creation; the
+ * id is persisted in org_billing_config so subsequent invoices
+ * reuse it.
+ *
+ * Returns the Stripe customer id (`cus_...`).
+ */
+export async function ensureStripeCustomerForOrg(params: {
+  zitadelOrgId: string;
+  // Snapshot taken at click-time, NOT at invoice issuance — the
+  // org's current address goes on the Stripe customer object.
+  // Stripe's address on file is independent of any one invoice.
+  companyName: string;
+  billingEmail: string;
+  address: {
+    line1: string;
+    postalCode: string;
+    city: string;
+    country: string; // ISO 3166-1 alpha-2 (e.g. "CH")
+  };
+}): Promise<string> {
+  // Lazy import to avoid pulling pg into edge-runtime modules that
+  // might import this file. Same pattern used elsewhere in lib/.
+  const { getOrgBillingConfig, updateOrgBillingConfig } = await import("./db");
+  const existing = await getOrgBillingConfig(params.zitadelOrgId);
+  if (existing.stripeCustomerId) {
+    return existing.stripeCustomerId;
+  }
+  const stripe = getStripeClient();
+  const customer = await stripe.customers.create({
+    email: params.billingEmail,
+    name: params.companyName,
+    address: {
+      line1: params.address.line1,
+      postal_code: params.address.postalCode,
+      city: params.address.city,
+      country: params.address.country,
+    },
+    metadata: {
+      zitadel_org_id: params.zitadelOrgId,
+    },
+  });
+  await updateOrgBillingConfig(params.zitadelOrgId, {
+    stripeCustomerId: customer.id,
+  });
+  return customer.id;
+}
+
+/**
+ * Create a Checkout Session for paying a single invoice by card.
+ *
+ * Design notes:
+ *
+ * - Single line item with the invoice total (gross, VAT included).
+ *   Our own invoice PDF already breaks down lines + VAT; the Stripe
+ *   page is the checkout, not a duplicate of the invoice.
+ *
+ * - `automatic_tax` is disabled because the invoice already has
+ *   VAT computed by our pipeline. Letting Stripe re-calculate
+ *   would double-charge or contradict our PDF.
+ *
+ * - `payment_method_types` is NOT set, so Stripe surfaces dynamic
+ *   payment methods configured on the account (cards, TWINT for
+ *   Swiss customers, Apple Pay, Google Pay, etc.) automatically.
+ *
+ * - `metadata` and `payment_intent_data.metadata` BOTH carry the
+ *   invoice id. The session-level copy is enough for the
+ *   `checkout.session.completed` webhook; the intent-level copy
+ *   lets us correlate refunds and disputes which fire on the
+ *   PaymentIntent and don't include session metadata.
+ *
+ * - `client_reference_id` is set to our invoice id as a stable
+ *   reference. Visible in the Stripe dashboard, useful for support.
+ *
+ * - `locale` follows the invoice's locale so the customer sees
+ *   the Stripe page in their language (frozen at invoice issue
+ *   time; consistent with PDF + email).
+ */
+export async function createCheckoutSessionForInvoice(params: {
+  invoice: Invoice;
+  customerId: string;
+  baseUrl: string;
+}): Promise<{ url: string; sessionId: string }> {
+  const stripe = getStripeClient();
+  const { invoice, customerId, baseUrl } = params;
+
+  // Stripe Checkout supports a limited set of locales; map our
+  // four to Stripe's codes and fall back to 'auto' if anything
+  // outside the set ever appears.
+  const stripeLocale: Stripe.Checkout.SessionCreateParams.Locale =
+    invoice.locale === "de"
+      ? "de"
+      : invoice.locale === "fr"
+      ? "fr"
+      : invoice.locale === "it"
+      ? "it"
+      : invoice.locale === "en"
+      ? "en"
+      : "auto";
+
+  const successUrl = `${baseUrl}/billing/${encodeURIComponent(invoice.invoiceNumber)}?paid=1&session_id={CHECKOUT_SESSION_ID}`;
+  const cancelUrl = `${baseUrl}/billing/${encodeURIComponent(invoice.invoiceNumber)}?cancelled=1`;
+
+  const session = await stripe.checkout.sessions.create({
+    mode: "payment",
+    customer: customerId,
+    client_reference_id: invoice.id,
+    locale: stripeLocale,
+    line_items: [
+      {
+        quantity: 1,
+        price_data: {
+          currency: "chf",
+          unit_amount: chfToRappen(invoice.totalChf),
+          product_data: {
+            name: `Invoice ${invoice.invoiceNumber}`,
+            description: `PieCed IT — ${invoice.periodStart.slice(0, 10)} → ${invoice.periodEnd.slice(0, 10)}`,
+          },
+        },
+      },
+    ],
+    metadata: {
+      invoice_id: invoice.id,
+      invoice_number: invoice.invoiceNumber,
+      zitadel_org_id: invoice.zitadelOrgId,
+    },
+    payment_intent_data: {
+      // Mirror invoice id at the PaymentIntent level so refunds &
+      // disputes (which fire on the PI, not the session) can be
+      // correlated to our invoice without an extra lookup.
+      metadata: {
+        invoice_id: invoice.id,
+        invoice_number: invoice.invoiceNumber,
+        zitadel_org_id: invoice.zitadelOrgId,
+      },
+      // Statement descriptor shown on the customer's card
+      // statement. Limited to 22 chars total; we use the prefix
+      // since Stripe will prepend the merchant name from the
+      // account anyway. Keep it short and recognisable.
+      description: `Invoice ${invoice.invoiceNumber}`,
+    },
+    success_url: successUrl,
+    cancel_url: cancelUrl,
+    // VAT is already in invoice.totalChf — don't let Stripe touch tax.
+    automatic_tax: { enabled: false },
+  });
+
+  if (!session.url) {
+    throw new Error(
+      `Stripe returned a session without a redirect URL (id=${session.id})`
+    );
+  }
+  return { url: session.url, sessionId: session.id };
+}