fix(types,utils,promotion): Move from total to original_total to resolve edge case for adjustments calculation (#13106)

* Move from total to original_total to resolve edge case in adjustment calculation

* Added changeset

* Added test case for correction

---------

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

.changeset/sour-horses-beam.md

@@ -0,0 +1,7 @@
+---
+"@medusajs/promotion": patch
+"@medusajs/types": patch
+"@medusajs/utils": patch
+---
+
+Moved calculation logic from total to original_total to ensure consistent base values

integration-tests/http/__tests__/cart/store/cart.spec.ts

@@ -3463,6 +3463,143 @@ medusaIntegrationTestRunner({
             })
           )
         })
+
+        it("should verify that reapplying the same promotion code after the cart total has been reduced to zero does not incorrectly remove existing adjustments", async () => {
+          const taxInclPromotion = (
+            await api.post(
+              `/admin/promotions`,
+              {
+                code: "PROMOTION_TAX_INCLUSIVE",
+                type: PromotionType.STANDARD,
+                status: PromotionStatus.ACTIVE,
+                is_tax_inclusive: true,
+                application_method: {
+                  type: "fixed",
+                  target_type: "items",
+                  allocation: "across",
+                  currency_code: "usd",
+                  value: 50,
+                },
+              },
+              adminHeaders
+            )
+          ).data.promotion
+
+          const product = (
+            await api.post(
+              `/admin/products`,
+              {
+                title: "Product for free",
+                description: "test",
+                options: [
+                  {
+                    title: "Size",
+                    values: ["S", "M", "L", "XL"],
+                  },
+                ],
+                variants: [
+                  {
+                    title: "S / Black",
+                    sku: "special-shirt",
+                    options: {
+                      Size: "S",
+                    },
+                    manage_inventory: false,
+                    prices: [
+                      {
+                        amount: 50,
+                        currency_code: "usd",
+                      },
+                    ],
+                  },
+                ],
+              },
+              adminHeaders
+            )
+          ).data.product
+
+          cart = (
+            await api.post(
+              `/store/carts`,
+              {
+                currency_code: "usd",
+                sales_channel_id: salesChannel.id,
+                region_id: region.id,
+                shipping_address: shippingAddressData,
+              },
+              storeHeadersWithCustomer
+            )
+          ).data.cart
+
+          cart = (
+            await api.post(
+              `/store/carts/${cart.id}/line-items`,
+              {
+                variant_id: product.variants[0].id,
+                quantity: 1,
+              },
+              storeHeaders
+            )
+          ).data.cart
+
+          let updated = await api.post(
+            `/store/carts/${cart.id}`,
+            {
+              promo_codes: [taxInclPromotion.code],
+            },
+            storeHeaders
+          )
+
+          expect(updated.status).toEqual(200)
+          expect(updated.data.cart).toEqual(
+            expect.objectContaining({
+              discount_total: 50,
+              original_total: 50,
+              total: 0,
+              items: expect.arrayContaining([
+                expect.objectContaining({
+                  is_tax_inclusive: true,
+                  adjustments: expect.arrayContaining([
+                    expect.objectContaining({
+                      code: taxInclPromotion.code,
+                      amount: 50,
+                      is_tax_inclusive: true,
+                    }),
+                  ]),
+                }),
+              ]),
+            })
+          )
+
+          let updatedAgain = await api.post(
+            `/store/carts/${cart.id}`,
+            {
+              promo_codes: [taxInclPromotion.code],
+            },
+            storeHeaders
+          )
+
+          expect(updatedAgain.status).toEqual(200)
+          expect(updatedAgain.data.cart).toEqual(
+            expect.objectContaining({
+              discount_total: 50,
+              original_total: 50,
+              total: 0,
+              items: expect.arrayContaining([
+                expect.objectContaining({
+                  is_tax_inclusive: true,
+                  adjustments: expect.arrayContaining([
+                    expect.objectContaining({
+                      code: taxInclPromotion.code,
+                      amount: 50,
+                      is_tax_inclusive: true,
+                    }),
+                  ]),
+                }),
+              ]),
+            })
+          )
+        })
       })
 
       describe("POST /store/carts/:id/customer", () => {

packages/core/types/src/promotion/common/compute-actions.ts

@@ -188,7 +188,7 @@ export interface ComputeActionItemLine extends Record<string, unknown> {
   /**
    * The total of the line item.
    */
-  total: BigNumberInput
+  original_total: BigNumberInput
 
   /**
    * Whether the line item is discountable.
@@ -218,7 +218,7 @@ export interface ComputeActionShippingLine extends Record<string, unknown> {
   /**
    * The total of the shipping method.
    */
-  total: BigNumberInput
+  original_total: BigNumberInput
 
   /**
    * The adjustments applied before on the shipping method.

packages/core/utils/src/totals/promotion/index.ts

@@ -53,8 +53,8 @@ function getLineItemSubtotal(lineItem) {
   return MathBN.div(lineItem.subtotal, lineItem.quantity)
 }
 
-function getLineItemTotal(lineItem) {
+function getLineItemOriginalTotal(lineItem) {
-  return MathBN.div(lineItem.total, lineItem.quantity)
+  return MathBN.div(lineItem.original_total, lineItem.quantity)
 }
 
 export function calculateAdjustmentAmountFromPromotion(
@@ -95,7 +95,7 @@ export function calculateAdjustmentAmountFromPromotion(
 
     const lineItemAmount = MathBN.mult(
       promotion.is_tax_inclusive
-        ? getLineItemTotal(lineItem)
+        ? getLineItemOriginalTotal(lineItem)
         : getLineItemSubtotal(lineItem),
       quantity
     )
@@ -134,11 +134,11 @@ export function calculateAdjustmentAmountFromPromotion(
   */
 
   const remainingItemAmount = MathBN.sub(
-    promotion.is_tax_inclusive ? lineItem.total : lineItem.subtotal,
+    promotion.is_tax_inclusive ? lineItem.original_total : lineItem.subtotal,
     promotion.applied_value
   )
   const itemAmount = MathBN.div(
-    promotion.is_tax_inclusive ? lineItem.total : lineItem.subtotal,
+    promotion.is_tax_inclusive ? lineItem.original_total : lineItem.subtotal,
     lineItem.quantity
   )
   const maximumPromotionAmount = MathBN.mult(

packages/modules/promotion/src/utils/compute-actions/line-items.ts

@@ -110,7 +110,7 @@ function applyPromotionToItems(
         MathBN.sub(
           MathBN.add(
             acc,
-            promotion.is_tax_inclusive ? item.total : item.subtotal
+            promotion.is_tax_inclusive ? item.original_total : item.subtotal
           ),
           appliedPromotionsMap.get(item.id) ?? 0
         ),
@@ -124,7 +124,10 @@ function applyPromotionToItems(
 
   for (const item of applicableItems) {
     if (
-      MathBN.lte(promotion.is_tax_inclusive ? item.total : item.subtotal, 0)
+      MathBN.lte(
+        promotion.is_tax_inclusive ? item.original_total : item.subtotal,
+        0
+      )
     ) {
       continue
     }