fix(medusa): totals calculation with gift card (#5075)

**What**
Resolve potential discrepency between what is calculated in the `createFromCart` and the cart/order totals calculation.
When the giftCard is taxable then the following calculation is applied 
```ts
cart.subtotal + cart.shipping_total - cart.discount_total
```
otherwise
```ts
 cart.subtotal +
          cart.shipping_total +
          cart.tax_total -
          cart.discount_total
```

Co-authored-by: Oli Juhl <59018053+olivermrbl@users.noreply.github.com>

.changeset/fifty-cooks-occur.md

@@ -0,0 +1,5 @@
+---
+"@medusajs/medusa": patch
+---
+
+fix(medusa): totals calculation with gift card

packages/medusa/src/services/__mocks__/new-totals.js

@@ -1,3 +1,5 @@
+const NewTotalsService = require("../new-totals")
+
 export const newTotalsServiceMock = {
   withTransaction: function () {
     return this
@@ -16,6 +18,23 @@ export const newTotalsServiceMock = {
   getShippingMethodTotals: jest.fn().mockImplementation((order, lineItems) => {
     return Promise.resolve({})
   }),
+  getGiftCardableAmount: jest
+    .fn()
+    .mockImplementation(
+      ({
+        gift_cards_taxable,
+        subtotal,
+        shipping_total,
+        discount_total,
+        tax_total,
+      }) => {
+        return Promise.resolve(
+          (gift_cards_taxable
+            ? subtotal + shipping_total - discount_total
+            : subtotal + shipping_total + tax_total - discount_total) || 0
+        )
+      }
+    ),
 }
 
 const mock = jest.fn().mockImplementation(() => {

packages/medusa/src/services/__tests__/order.js

@@ -364,6 +364,7 @@ describe("OrderService", () => {
         subtotal: 100,
         total: 100,
         discount_total: 0,
+        gift_card_total: 100,
       }
 
       orderService.cartService_.retrieveWithTotals = () => {

packages/medusa/src/services/cart.ts

@@ -1,8 +1,11 @@
+import { FlagRouter, isDefined, MedusaError } from "@medusajs/utils"
+import { isEmpty, isEqual } from "lodash"
+import { DeepPartial, EntityManager, In, IsNull, Not } from "typeorm"
 import {
   Address,
   Cart,
-  CustomShippingOption,
   Customer,
+  CustomShippingOption,
   Discount,
   DiscountRule,
   DiscountRuleType,
@@ -22,13 +25,13 @@ import {
   CartCreateProps,
   CartUpdateProps,
   FilterableCartProps,
+  isCart,
   LineItemUpdate,
   LineItemValidateData,
-  isCart,
 } from "../types/cart"
 import {
-  CustomShippingOptionService,
   CustomerService,
+  CustomShippingOptionService,
   DiscountService,
   EventBusService,
   GiftCardService,
@@ -48,21 +51,16 @@ import {
   TaxProviderService,
   TotalsService,
 } from "."
-import { DeepPartial, EntityManager, In, IsNull, Not } from "typeorm"
 import { IPriceSelectionStrategy, TransactionBaseService } from "../interfaces"
-import { MedusaError, isDefined } from "medusa-core-utils"
+import IsolateProductDomainFeatureFlag from "../loaders/feature-flags/isolate-product-domain"
+import SalesChannelFeatureFlag from "../loaders/feature-flags/sales-channels"
 import { buildQuery, isString, setMetadata } from "../utils"
-import { isEmpty, isEqual } from "lodash"
 
 import { AddressRepository } from "../repositories/address"
 import { CartRepository } from "../repositories/cart"
-import { FlagRouter } from "@medusajs/utils"
-import { IsNumber } from "class-validator"
-import IsolateProductDomainFeatureFlag from "../loaders/feature-flags/isolate-product-domain"
 import { LineItemRepository } from "../repositories/line-item"
 import { PaymentSessionInput } from "../types/payment"
 import { PaymentSessionRepository } from "../repositories/payment-session"
-import SalesChannelFeatureFlag from "../loaders/feature-flags/sales-channels"
 import { ShippingMethodRepository } from "../repositories/shipping-method"
 import { validateEmail } from "../utils/is-email"
 
@@ -2753,8 +2751,21 @@ class CartService extends TransactionBaseService {
       }
     )
 
+    cart.tax_total = cart.item_tax_total + cart.shipping_tax_total
+
+    cart.raw_discount_total = cart.discount_total
+    cart.discount_total = Math.round(cart.discount_total)
+
+    const giftCardableAmount = this.newTotalsService_.getGiftCardableAmount({
+      gift_cards_taxable: cart.region?.gift_cards_taxable,
+      subtotal: cart.subtotal,
+      discount_total: cart.discount_total,
+      shipping_total: cart.shipping_total,
+      tax_total: cart.tax_total,
+    })
+
     const giftCardTotal = await this.newTotalsService_.getGiftCardTotals(
-      cart.subtotal - cart.discount_total,
+      giftCardableAmount,
       {
         region: cart.region,
         giftCards: cart.gift_cards,
@@ -2764,11 +2775,6 @@ class CartService extends TransactionBaseService {
     cart.gift_card_total = giftCardTotal.total || 0
     cart.gift_card_tax_total = giftCardTotal.tax_total || 0
 
-    cart.tax_total = cart.item_tax_total + cart.shipping_tax_total
-
-    cart.raw_discount_total = cart.discount_total
-    cart.discount_total = Math.round(cart.discount_total)
-
     cart.total =
       cart.subtotal +
       cart.shipping_total +

packages/medusa/src/services/new-totals.ts

@@ -1,5 +1,5 @@
 import { FlagRouter } from "@medusajs/utils"
-import { MedusaError, isDefined } from "medusa-core-utils"
+import { isDefined, MedusaError } from "medusa-core-utils"
 import { EntityManager } from "typeorm"
 import {
   ITaxCalculationStrategy,
@@ -635,6 +635,26 @@ export default class NewTotalsService extends TransactionBaseService {
     return shippingMethodsTotals
   }
 
+  getGiftCardableAmount({
+    gift_cards_taxable,
+    subtotal,
+    shipping_total,
+    discount_total,
+    tax_total,
+  }: {
+    gift_cards_taxable?: boolean
+    subtotal: number
+    shipping_total: number
+    discount_total: number
+    tax_total: number
+  }): number {
+    return (
+      (gift_cards_taxable
+        ? subtotal + shipping_total - discount_total
+        : subtotal + shipping_total + tax_total - discount_total) || 0
+    )
+  }
+
   /**
    * Calculate and return the shipping method totals
    * @param shippingMethod

packages/medusa/src/services/order.ts

@@ -725,12 +725,8 @@ class OrderService extends TransactionBaseService {
         )
       }
 
-      const giftCardableAmount =
+      let giftCardableAmountBalance = cart.gift_card_total ?? 0
-        (cart.region?.gift_cards_taxable
-          ? cart.subtotal! - cart.discount_total!
-          : cart.total! + cart.gift_card_total!) || 0 // we re add the gift card total to compensate the fact that the decorate total already removed this amount from the total
 
-      let giftCardableAmountBalance = giftCardableAmount
       const giftCardService = this.giftCardService_.withTransaction(manager)
 
       // Order the gift cards by first ends_at date, then remaining amount. To ensure largest possible amount left, for longest possible time.
@@ -739,6 +735,7 @@ class OrderService extends TransactionBaseService {
         const bEnd = b.ends_at ?? new Date(2100, 1, 1)
         return aEnd.getTime() - bEnd.getTime() || a.balance - b.balance
       })
+
       for (const giftCard of orderedGiftCards) {
         const newGiftCardBalance = Math.max(
           0,
@@ -1898,8 +1895,20 @@ class OrderService extends TransactionBaseService {
       }
     )
 
+    order.item_tax_total = item_tax_total
+    order.shipping_tax_total = shipping_tax_total
+    order.tax_total = item_tax_total + shipping_tax_total
+
+    const giftCardableAmount = this.newTotalsService_.getGiftCardableAmount({
+      gift_cards_taxable: order.region?.gift_cards_taxable,
+      subtotal: order.subtotal,
+      discount_total: order.discount_total,
+      shipping_total: order.shipping_total,
+      tax_total: order.tax_total,
+    })
+
     const giftCardTotal = await this.newTotalsService_.getGiftCardTotals(
-      order.subtotal - order.discount_total,
+      giftCardableAmount,
       {
         region: order.region,
         giftCards: order.gift_cards,
@@ -1909,12 +1918,7 @@ class OrderService extends TransactionBaseService {
     order.gift_card_total = giftCardTotal.total || 0
     order.gift_card_tax_total = giftCardTotal.tax_total || 0
 
-    order.item_tax_total = item_tax_total
+    order.tax_total -= order.gift_card_tax_total
-    order.shipping_tax_total = shipping_tax_total
-    order.tax_total =
-      order.item_tax_total +
-      order.shipping_tax_total -
-      order.gift_card_tax_total
 
     for (const swap of order.swaps ?? []) {
       swap.additional_items = swap.additional_items.map((item) => {