B2B-88: add starter kit structure and elements

packages/billing/lemon-squeezy/src/services/create-lemon-squeezy-checkout.ts

@@ -0,0 +1,76 @@
+import {
+  NewCheckout,
+  createCheckout,
+  getCustomer,
+} from '@lemonsqueezy/lemonsqueezy.js';
+import { z } from 'zod';
+
+import type { CreateBillingCheckoutSchema } from '@kit/billing/schema';
+
+import { getLemonSqueezyEnv } from '../schema/lemon-squeezy-server-env.schema';
+import { initializeLemonSqueezyClient } from './lemon-squeezy-sdk';
+
+/**
+ * Creates a checkout for a Lemon Squeezy product.
+ */
+export async function createLemonSqueezyCheckout(
+  params: z.infer<typeof CreateBillingCheckoutSchema>,
+) {
+  await initializeLemonSqueezyClient();
+
+  const lineItem = params.plan.lineItems[0];
+
+  if (!lineItem) {
+    throw new Error('No line items found in subscription');
+  }
+
+  const env = getLemonSqueezyEnv();
+
+  const storeId = Number(env.storeId);
+  const variantId = Number(lineItem.id);
+
+  const customer = params.customerId
+    ? await getCustomer(params.customerId)
+    : null;
+
+  let customerEmail = params.customerEmail;
+
+  // if we can find an existing customer using the ID,
+  // we use the email from the customer object so that we can
+  // link the previous subscription to this one
+  // otherwise it will create a new customer if another email is provided (ex. a different team member)
+  if (customer?.data) {
+    customerEmail = customer.data.data.attributes.email;
+  }
+
+  const newCheckout: NewCheckout = {
+    checkoutOptions: {
+      embed: true,
+      media: true,
+      logo: true,
+      discount: params.enableDiscountField ?? false,
+    },
+    checkoutData: {
+      email: customerEmail,
+      variantQuantities: params.variantQuantities.map((item) => {
+        return {
+          quantity: item.quantity,
+          variantId: Number(item.variantId),
+        };
+      }),
+      custom: {
+        account_id: params.accountId,
+      },
+    },
+    productOptions: {
+      redirectUrl: params.returnUrl,
+      // only show the selected variant ID
+      enabledVariants: [variantId],
+    },
+    expiresAt: null,
+    preview: true,
+    testMode: process.env.NODE_ENV !== 'production',
+  };
+
+  return createCheckout(storeId, variantId, newCheckout);
+}