apps/backend/src/app/api/latest/internal/payments/transactions/refund/route.tsx (3)

141-162: Duplicated refund validation logic between subscription and one-time-purchase branches.

The validation and conversion logic (lines 141-162 for subscriptions and 189-209 for one-time purchases) is nearly identical. Consider extracting this into a shared helper function to reduce duplication and improve maintainability.

♻️ Suggested refactor

+function computeAndValidateRefundAmount(options: {
+  refundAmountUsd: MoneyAmount,
+  product: InferType<typeof productSchema>,
+  priceId: string | null,
+  quantity: number,
+}): number {
+  const totalStripeUnits = getTotalUsdStripeUnits({
+    product: options.product,
+    priceId: options.priceId,
+    quantity: options.quantity,
+  });
+  const refundAmountStripeUnits = moneyAmountToStripeUnits(options.refundAmountUsd, USD_CURRENCY);
+  if (refundAmountStripeUnits <= 0) {
+    throw new KnownErrors.SchemaError("Refund amount must be greater than zero.");
+  }
+  if (refundAmountStripeUnits > totalStripeUnits) {
+    throw new KnownErrors.SchemaError("Refund amount cannot exceed the charged amount.");
+  }
+  return refundAmountStripeUnits;
+}

Then use this helper in both branches.

Also applies to: 189-209

---

148-151: Unsafe type casting of database JSON field.

The subscription.product is cast directly to InferType<typeof productSchema> without validation. If the stored JSON doesn't match the expected schema (due to schema evolution or data corruption), this could cause runtime errors downstream.

Consider validating the product data before use:

♻️ Suggested validation

-      const totalStripeUnits = getTotalUsdStripeUnits({
-        product: subscription.product as InferType<typeof productSchema>,
-        priceId: subscription.priceId ?? null,
-        quantity: subscription.quantity,
-      });
+      const validatedProduct = productSchema.validateSync(subscription.product);
+      const totalStripeUnits = getTotalUsdStripeUnits({
+        product: validatedProduct,
+        priceId: subscription.priceId ?? null,
+        quantity: subscription.quantity,
+      });

Based on learnings, code defensively with good error messages.

---

141-141: Unnecessary let declaration with unused null initialization.

refundAmountStripeUnits is declared as let ... | null = null but is immediately assigned without the null ever being read. Consider using const at the point of assignment:

♻️ Suggested fix

-      let refundAmountStripeUnits: number | null = null;
       // ... validation code ...
-      refundAmountStripeUnits = moneyAmountToStripeUnits(refundAmountUsd as MoneyAmount, USD_CURRENCY);
+      const refundAmountStripeUnits = moneyAmountToStripeUnits(refundAmountUsd as MoneyAmount, USD_CURRENCY);

Also applies to: 189-189

apps/e2e/tests/backend/endpoints/api/v1/internal/transactions-refund.test.ts (2)

134-135: Avoid any type for transaction filtering.

The any type here bypasses type checking. Per coding guidelines, avoid any and leave a comment if unavoidable.

♻️ Suggested fix

-  const purchaseTransaction = transactionsRes.body.transactions.find((tx: any) => tx.type === "purchase");
+  // Transaction type from API response - typed loosely since this is test code
+  const purchaseTransaction = transactionsRes.body.transactions.find(
+    (tx: { type: string }) => tx.type === "purchase"
+  );

---

326-390: Consider adding negative test cases for refund validation.

The tests cover successful partial and quantity-based refunds, but there are no tests verifying the validation errors for:

• Refund amount exceeding the charged amount
• Refund quantity exceeding the purchased quantity
• Invalid entry_index values

These would help ensure the backend validation logic is working correctly.

apps/dashboard/src/components/data-table/transaction-table.tsx (1)

43-43: USD_CURRENCY could be undefined without a fallback.

Unlike the backend which uses ?? throwErr(...), the frontend USD_CURRENCY could be undefined if USD is not found in SUPPORTED_CURRENCIES. While this is unlikely, defensive coding would catch configuration errors early.

♻️ Suggested fix

-const USD_CURRENCY = SUPPORTED_CURRENCIES.find((currency) => currency.code === 'USD');
+const USD_CURRENCY = SUPPORTED_CURRENCIES.find((currency) => currency.code === 'USD')
+  ?? throwErr("USD currency configuration missing in SUPPORTED_CURRENCIES");

Based on learnings, prefer ?? throwErr(...) over potentially undefined values.

apps/dashboard/src/components/data-table/transaction-table.tsx (1)

42-42: Prefer interface for RefundEntrySelection.

This is an object shape and should use interface to match the project’s TypeScript style. As per coding guidelines, please prefer interfaces for object shapes.

♻️ Suggested refactor

-type RefundEntrySelection = { entryIndex: number, quantity: number };
+interface RefundEntrySelection {
+  entryIndex: number;
+  quantity: number;
+}

apps/backend/src/app/api/latest/internal/payments/transactions/refund/route.tsx (1)

29-32: Prefer interface for RefundEntrySelection.

This is an object shape and should use interface to align with the TypeScript style rules. As per coding guidelines, please prefer interfaces for object shapes.

♻️ Suggested refactor

-type RefundEntrySelection = {
-  entry_index: number,
-  quantity: number,
-};
+interface RefundEntrySelection {
+  entry_index: number;
+  quantity: number;
+}

apps/backend/src/app/api/latest/internal/payments/transactions/refund/route.tsx (3)

17-27: Type assertion bypasses MoneyAmount format validation.

The usdPrice is checked to be a string, but the as MoneyAmount cast at line 26 assumes it's in a valid money format (e.g., "10.00"). If the product's price data is malformed, this could produce unexpected results from moneyAmountToStripeUnits.

Consider validating the format or using a parsing function that throws on invalid input.

---

29-32: Prefer interface over type for object shapes.

Per coding guidelines, use interface for defining object shapes in TypeScript.

Suggested change

-type RefundEntrySelection = {
-  entry_index: number,
-  quantity: number,
-};
+interface RefundEntrySelection {
+  entry_index: number;
+  quantity: number;
+}

---

146-146: Unnecessary null initialization.

refundAmountStripeUnits is initialized to null but immediately assigned a value on the next few lines. The null initialization is unnecessary.

Suggested change (example for line 146)

-      let refundAmountStripeUnits: number | null = null;
       const transaction = buildSubscriptionTransaction({ subscription });
       validateRefundEntries({
         entries: transaction.entries,
         refundEntries,
       });
       const refundedQuantity = getRefundedQuantity(refundEntries);
       const totalStripeUnits = getTotalUsdStripeUnits({
         product: subscription.product as InferType<typeof productSchema>,
         priceId: subscription.priceId ?? null,
         quantity: subscription.quantity,
       });
-      refundAmountStripeUnits = moneyAmountToStripeUnits(refundAmountUsd as MoneyAmount, USD_CURRENCY);
+      const refundAmountStripeUnits = moneyAmountToStripeUnits(refundAmountUsd as MoneyAmount, USD_CURRENCY);

Also applies to: 230-230