Fix discount code Stripe/DB drift on creation failure (#3985)

Author: pepeladeira

apps/web/app/(ee)/api/discount-codes/route.ts

@@ -96,7 +96,7 @@ export const POST = withWorkspace(
       const duplicateByCode = await prisma.discountCode.findUnique({
         where: {
           programId_code: {
-            programId,
+            programId: discount.programId,
             code,
           },
         },

apps/web/lib/discounts/create-discount-code.ts

@@ -1,6 +1,7 @@
 import { createId } from "@/lib/api/create-id";
+import { DubApiError } from "@/lib/api/errors";
 import { prisma } from "@dub/prisma";
-import { Discount, Link, Partner, Project } from "@dub/prisma/client";
+import { Discount, Link, Partner, Prisma, Project } from "@dub/prisma/client";
 import { constructDiscountCode } from "./construct-discount-code";
 import { getDiscountProvider } from "./discount-provider";
 
@@ -19,33 +20,90 @@ export async function createDiscountCode({
   discount,
   code,
 }: CreateDiscountCodeArgs) {
-  let finalCode = code;
-
-  // Construct the discount code if no code is provided
-  if (!finalCode) {
-    finalCode = constructDiscountCode({
+  const finalCode =
+    code ||
+    constructDiscountCode({
       partner,
       discount,
     });
+
+  const linkWithCode = await prisma.link.findUnique({
+    where: { id: link.id },
+    select: { discountCode: { select: { code: true } } },
+  });
+
+  if (linkWithCode?.discountCode) {
+    throw new DubApiError({
+      code: "bad_request",
+      message: `This link already has a discount code (${linkWithCode.discountCode.code}) assigned.`,
+    });
   }
 
   const discountProvider = getDiscountProvider(discount.provider);
 
-  const discountCode = await discountProvider.createDiscountCode({
-    workspace,
-    discount,
-    code: finalCode,
-    shouldRetry: code ? false : true,
-  });
+  let externalDiscountCode: Awaited<
+    ReturnType<typeof discountProvider.createDiscountCode>
+  >;
 
-  return await prisma.discountCode.create({
-    data: {
-      id: createId({ prefix: "dcode_" }),
-      code: discountCode.code,
-      programId: discount.programId,
-      partnerId: partner.id,
-      linkId: link.id,
-      discountId: discount.id,
-    },
-  });
+  try {
+    externalDiscountCode = await discountProvider.createDiscountCode({
+      workspace,
+      discount,
+      code: finalCode,
+      shouldRetry: code ? false : true,
+    });
+  } catch (error) {
+    const message = error?.raw?.message || error?.message || "";
+    const isDuplicateCode =
+      message.includes("already exists") ||
+      error?.code === "TAKEN" ||
+      error?.code === "DUPLICATE";
+
+    if (isDuplicateCode) {
+      throw new DubApiError({
+        code: "conflict",
+        message: `The discount code ${finalCode} is already in use. Please choose a different code.`,
+      });
+    }
+
+    throw error;
+  }
+
+  try {
+    return await prisma.discountCode.create({
+      data: {
+        id: createId({ prefix: "dcode_" }),
+        code: externalDiscountCode.code,
+        programId: discount.programId,
+        partnerId: partner.id,
+        linkId: link.id,
+        discountId: discount.id,
+      },
+    });
+  } catch (error) {
+    try {
+      await discountProvider.disableDiscountCode({
+        workspace,
+        code: externalDiscountCode.code,
+      });
+    } catch (rollbackError) {
+      console.error("Failed to rollback external discount code", {
+        code: externalDiscountCode.code,
+        rollbackError,
+      });
+    }
+
+    if (
+      error instanceof Prisma.PrismaClientKnownRequestError &&
+      error.code === "P2002"
+    ) {
+      throw new DubApiError({
+        code: "conflict",
+        message:
+          "This discount code is already in use, or this link already has a code. Please refresh and try again.",
+      });
+    }
+
+    throw error;
+  }
 }