2 discount bug fixes (multiple discounts + shipping discounts)

.changeset/cool-swans-wonder.md

@@ -0,0 +1,5 @@
+---
+"shopify-buy": patch
+---
+
+Fix bug where a shipping discount could appear as if it was a line item discount

.changeset/tough-phones-sip.md

@@ -0,0 +1,5 @@
+---
+"shopify-buy": patch
+---
+
+Fix bug where adding multiple discount codes to the cart could inadvertently remove some discounts

README.md

@@ -70,6 +70,7 @@ If you migrate to Storefront API Client, there is virtually no use case that can
 | shippingLine     | ⚠️            | Not supported. Defaults to `null`  | Same as above                                                                                                                                                                                                           |
 | taxExempt        | ⚠️            | Not supported. Defaults to `false` | The [Cart API](https://shopify.dev/docs/api/storefront/2025-01/objects/cart) is not tax aware, as taxes are currently handled in the Checkout flow. Remove any existing code depending on this field.               |
 | taxesIncluded    | ⚠️            | Not supported. Defaults to `false` | Same as above                                                                                                                                                                                                           |
+| discountApplications | ✅⚠️          | If a buyer's shipping address is unknown and a shipping discount is applied, shipping discount information is **no longer** returned | In this situation, the [Cart API](https://shopify.dev/docs/api/storefront/2025-01/objects/cart) does not return any information about the value of the shipping discount (eg: whether it's a 100% discount or a $5 off discount)
 
 #### Updated `.checkout` methods
 

src/checkout-resource.js

@@ -201,20 +201,41 @@ class CheckoutResource extends Resource {
    * @return {Promise|GraphModel} A promise resolving with the updated checkout.
    */
   addDiscount(checkoutId, discountCode) {
-    return this.fetch(checkoutId).then((checkout) => {
-      const existingRootCodes = checkout.discountApplications.map(
-        (discountApplication) => discountApplication.code
-      );
+    // We want access to Cart's `discountCodes` field, so we can't just use the
+    // existing `fetch` method since that also maps and removes the `discountCodes` field.
+    // We must therefore look at the raw Cart data to be able to see ALL existing discount codes,
+    // whether they are `applied` or not.
+
+    // The query below is identical to the `fetch` method's query EXCEPT we don't call `mapCartPayload` here
+    return this.graphQLClient.send(cartNodeQuery, {id: checkoutId}).then(({model, data}) => {
+      return new Promise((resolve, reject) => {
+        try {
+          const cart = data.cart || data.node;
+
+          if (!cart) {
+            return resolve(null);
+          }
 
-      const existingLineCodes = checkout.lineItems.map((lineItem) => {
-        return lineItem.discountAllocations.map(
-          ({discountApplication}) => discountApplication.code
-        );
-      });
+          return this.graphQLClient
+            .fetchAllPages(model.cart.lines, {pageSize: 250})
+            .then((lines) => {
+              model.cart.attrs.lines = lines;
+
+              return resolve(model.cart);
+            });
+        } catch (error) {
+          if (error) {
+            reject(error);
+          } else {
+            reject([{message: 'an unknown error has occurred.'}]);
+          }
+        }
 
-      // get unique applied codes
-      const existingCodes = Array.from(
-        new Set([...existingRootCodes, ...existingLineCodes.flat()])
+        return resolve(null);
+      });
+    }).then((checkout) => {
+      const existingCodes = checkout.discountCodes.map(
+        (code) => code.code
       );
 
       const variables = this.inputMapper.addDiscount(

src/utilities/cart-discount-mapping.js

@@ -152,44 +152,84 @@ export function discountMapper({cartLineItems, cartDiscountAllocations, cartDisc
     };
   }
 
+  // For each discount allocation, move the code/title field to be inside the discountApplication.
+  // This is because the code/title field is part of the discount allocation for a Cart, but part of
+  // the discount application for a Checkout
+  //
+  // CART EXAMPLE:                                  | CHECKOUT EXAMPLE:
+  // "cart": {                                      | "checkout": {
+  //   "discountAllocations": [                     |   "discountApplications": {
+  //     {                                          |     "nodes": [
+  //       "discountedAmount": {                    |       {
+  //         "amount": "18.0",                      |         "targetSelection": "ALL",
+  //         "currencyCode": "CAD"                  |         "allocationMethod": "EACH",
+  //       },                                       |         "targetType": "SHIPPING_LINE",
+  //       "discountApplication": {                 |         "value": {
+  //         "targetType": "SHIPPING_LINE",         |           "percentage": 100.0
+  //         "allocationMethod": "EACH",            |         },
+  //         "targetSelection": "ALL",              |         "code": "FREESHIPPINGALLCOUNTRIES",
+  //         "value": {                             |         "applicable": true
+  //           "percentage": 100.0                  |       }
+  //         }                                      |     ]
+  //       },                                       |   },
+  //       "code": "FREESHIPPINGALLCOUNTRIES"       | }
+  //     }                                          |
+  //   ]                                            |
+  //   "discountCodes": [                           |
+  //     {                                          |
+  //       "code": "FREESHIPPINGALLCOUNTRIES",      |
+  //       "applicable": true                       |
+  //     }                                          |
+  //   ],                                           |
+  // }                                              |
   convertToCheckoutDiscountApplicationType(cartLineItems, cartDiscountAllocations);
 
+  // While both the Cart and Checkout API return discount allocations for line items and therefore appear similar, they are
+  // substantially different in how they handle order-level discounts.
+  //
+  // The Checkout API ONLY returns discount allocations as a field on line items (for both product-level and order-level discounts).
+  // Shipping discounts are only returned as part of `checkout.discountApplications` (and do NOT have any discount allocations).
+  //
+  // Unlike the Checkout API, the Cart API returns different types of discount allocations in 2 different places:
+  // 1. Discount allocations as a field on line items (for product-level discounts)
+  // 2. Discount allocations as a field on the Cart itself (for order-level discounts and shipping discounts)
+  //
+  // Therefore, to map the Cart API payload to the equivalent Checkout API payload, we need to go through all of the order-level discount
+  // allocations on the *Cart*, and determine which line item the discount is allocated to. But first, we must go through the cart-level
+  // discount allocations to split them into order-level and shipping-level discount allocations.
+  //     - ONLY the order-level discount allocations go onto line items.
+  const [shippingDiscountAllocations, orderLevelDiscountAllocations] = cartDiscountAllocations.reduce((acc, discountAllocation) => {
+    if (discountAllocation.discountApplication.targetType === 'SHIPPING_LINE') {
+      acc[0].push(discountAllocation);
+    } else {
+      acc[1].push(discountAllocation);
+    }
+
+    return acc;
+  }, [[], []]);
   const cartLinesWithAllDiscountAllocations =
     mergeCartOrderLevelDiscountAllocationsToCartLineDiscountAllocations({
       lineItems: cartLineItems,
       orderLevelDiscountAllocationsForLines: findLineIdForEachOrderLevelDiscountAllocation(
         cartLineItems,
-        cartDiscountAllocations
+        orderLevelDiscountAllocations
       )
     });
 
+  // The Cart API and Checkout API have almost identical fields for discount applications, but the `value` field's behaviour (for fixed-amount discounts)
+  // is different.
+  //
+  // With the Checkout API, the `value` field of a discount application is equal to the SUM of all of the `allocatedAmount`s of all of the discount allocations
+  // for that discount.
+  // With the Cart API, the `value` field of a discount application is always equal to the `allocatedAmount` of the discount allocation that the discount
+  // application is inside of. Therefore, to map this to the equivalent Checkout API payload, we need to find all of the discount allocations for the same
+  // discount, and sum up all of the allocated amounts to determine the TOTAL value of the discount.
   const discountIdToDiscountApplicationMap = generateDiscountApplications(
     cartLinesWithAllDiscountAllocations,
+    shippingDiscountAllocations,
     cartDiscountCodes
   );
 
-  cartDiscountCodes.forEach(({code, codeIsApplied}) => {
-    if (!codeIsApplied) { return; }
-
-    // Check if the code exists in the map (case-insensitive)
-    let found = false;
-
-    for (const [key] of discountIdToDiscountApplicationMap) {
-      if (key.toLowerCase() === code.toLowerCase()) {
-        found = true;
-        break;
-      }
-    }
-    if (!found) {
-      throw new Error(
-        `Discount code ${code} not found in discount application map. 
-        Discount application map: ${JSON.stringify(
-          discountIdToDiscountApplicationMap
-        )}`
-      );
-    }
-  });
-
   return {
     discountApplications: Array.from(
       discountIdToDiscountApplicationMap.values()
@@ -222,7 +262,7 @@ function mergeCartOrderLevelDiscountAllocationsToCartLineDiscountAllocations({
   });
 }
 
-function generateDiscountApplications(cartLinesWithAllDiscountAllocations, discountCodes) {
+function generateDiscountApplications(cartLinesWithAllDiscountAllocations, shippingDiscountAllocations, discountCodes) {
   const discountIdToDiscountApplicationMap = new Map();
 
   if (!cartLinesWithAllDiscountAllocations) { return discountIdToDiscountApplicationMap; }
@@ -231,86 +271,94 @@ function generateDiscountApplications(cartLinesWithAllDiscountAllocations, disco
     if (!discountAllocations) { return; }
 
     discountAllocations.forEach((discountAllocation) => {
-      const discountApp = discountAllocation.discountApplication;
-      const discountId = getDiscountAllocationId(discountAllocation);
+      createCheckoutDiscountApplicationFromCartDiscountAllocation(discountAllocation, discountIdToDiscountApplicationMap, discountCodes);
+    });
+  });
+
+  shippingDiscountAllocations.forEach((discountAllocation) => {
+    createCheckoutDiscountApplicationFromCartDiscountAllocation(discountAllocation, discountIdToDiscountApplicationMap, discountCodes);
+  });
+
+  return discountIdToDiscountApplicationMap;
+}
+
+function createCheckoutDiscountApplicationFromCartDiscountAllocation(discountAllocation, discountIdToDiscountApplicationMap, discountCodes) {
+  const discountApp = discountAllocation.discountApplication;
+  const discountId = getDiscountAllocationId(discountAllocation);
 
-      if (!discountId) {
+  if (!discountId) {
+    throw new Error(
+      `Discount allocation must have either code or title in discountApplication: ${JSON.stringify(
+        discountAllocation
+      )}`
+    );
+  }
+
+  if (discountIdToDiscountApplicationMap.has(discountId.toLowerCase())) {
+    const existingDiscountApplication =
+      discountIdToDiscountApplicationMap.get(discountId.toLowerCase());
+
+    // if existingDiscountApplication.value is an amount rather than a percentage discount
+    if (existingDiscountApplication.value && 'amount' in existingDiscountApplication.value) {
+      existingDiscountApplication.value = {
+        amount: (Number(existingDiscountApplication.value.amount) + Number(discountAllocation.discountedAmount.amount)).toFixed(2),
+        currencyCode: existingDiscountApplication.value.currencyCode,
+        type: existingDiscountApplication.value.type
+      };
+    }
+  } else {
+    let discountApplication = {
+      __typename: 'DiscountApplication',
+      targetSelection: discountApp.targetSelection,
+      allocationMethod: discountApp.allocationMethod,
+      targetType: discountApp.targetType,
+      value: discountApp.value,
+      hasNextPage: false,
+      hasPreviousPage: false
+    };
+
+    if ('code' in discountAllocation.discountApplication) {
+      const discountCode = discountCodes.find(
+        ({code}) => code.toLowerCase() === discountId.toLowerCase()
+      );
+
+      if (!discountCode) {
         throw new Error(
-          `Discount allocation must have either code or title in discountApplication: ${JSON.stringify(
-            discountAllocation
+          `Discount code ${discountId} not found in cart discount codes. Discount codes: ${JSON.stringify(
+            discountCodes
           )}`
         );
       }
-
-      if (discountIdToDiscountApplicationMap.has(discountId.toLowerCase())) {
-        const existingDiscountApplication =
-          discountIdToDiscountApplicationMap.get(discountId.toLowerCase());
-
-        // if existingDiscountApplication.value is an amount rather than a percentage discount
-        if (existingDiscountApplication.value && 'amount' in existingDiscountApplication.value) {
-          existingDiscountApplication.value = {
-            amount: (Number(existingDiscountApplication.value.amount) + Number(discountAllocation.discountedAmount.amount)).toFixed(2),
-            currencyCode: existingDiscountApplication.value.currencyCode,
-            type: existingDiscountApplication.value.type
-          };
+      discountApplication = Object.assign({}, discountApplication, {
+        code: discountAllocation.discountApplication.code,
+        applicable: discountCode.applicable,
+        type: {
+          fieldBaseTypes: {
+            applicable: 'Boolean',
+            code: 'String'
+          },
+          implementsNode: false,
+          kind: 'OBJECT',
+          name: 'DiscountApplication'
         }
-      } else {
-        let discountApplication = {
-          __typename: 'DiscountApplication',
-          targetSelection: discountApp.targetSelection,
-          allocationMethod: discountApp.allocationMethod,
-          targetType: discountApp.targetType,
-          value: discountApp.value,
-          hasNextPage: false,
-          hasPreviousPage: false
-        };
-
-        if ('code' in discountAllocation.discountApplication) {
-          const discountCode = discountCodes.find(
-            ({code}) => code.toLowerCase() === discountId.toLowerCase()
-          );
-
-          if (!discountCode) {
-            throw new Error(
-              `Discount code ${discountId} not found in cart discount codes. Discount codes: ${JSON.stringify(
-                discountCodes
-              )}`
-            );
-          }
-          discountApplication = Object.assign({}, discountApplication, {
-            code: discountAllocation.discountApplication.code,
-            applicable: discountCode.applicable,
-            type: {
-              fieldBaseTypes: {
-                applicable: 'Boolean',
-                code: 'String'
-              },
-              implementsNode: false,
-              kind: 'OBJECT',
-              name: 'DiscountApplication'
-            }
-          });
-        } else {
-          discountApplication = Object.assign({}, discountApplication, {
-            title: discountAllocation.discountApplication.title,
-            type: {
-              fieldBaseTypes: {
-                applicable: 'Boolean',
-                title: 'String'
-              },
-              implementsNode: false,
-              kind: 'OBJECT',
-              name: 'DiscountApplication'
-            }
-          });
+      });
+    } else {
+      discountApplication = Object.assign({}, discountApplication, {
+        title: discountAllocation.discountApplication.title,
+        type: {
+          fieldBaseTypes: {
+            applicable: 'Boolean',
+            title: 'String'
+          },
+          implementsNode: false,
+          kind: 'OBJECT',
+          name: 'DiscountApplication'
         }
+      });
+    }
 
-        discountIdToDiscountApplicationMap.set(discountId.toLowerCase(), discountApplication);
-      }
-    });
-  });
-
-  return discountIdToDiscountApplicationMap;
+    discountIdToDiscountApplicationMap.set(discountId.toLowerCase(), discountApplication);
+  }
 }
 
 export function deepSortLines(lineItems) {