Adjust Tips Correctly for Partial Fills

src/utils/fulfill.ts

@@ -44,6 +44,7 @@ import {
   areAllCurrenciesSame,
   mapOrderAmountsFromFilledStatus,
   mapOrderAmountsFromUnitsToFill,
+  adjustTipsForPartialFills,
   totalItemsAmount,
 } from "./order";
 import {
@@ -377,11 +378,17 @@ export function fulfillStandardOrder(
         totalSize,
       });
 
+  let adjustedTips: ConsiderationItem[] = [];
+
+  if (tips.length > 0) {
+    adjustedTips = adjustTipsForPartialFills(tips, unitsToFill, totalSize);
+  }
+
   const {
     parameters: { offer, consideration },
   } = orderWithAdjustedFills;
 
-  const considerationIncludingTips = [...consideration, ...tips];
+  const considerationIncludingTips = [...consideration, ...adjustedTips];
 
   const offerCriteriaItems = offer.filter(({ itemType }) =>
     isCriteriaItem(itemType),

src/utils/order.ts

@@ -273,6 +273,32 @@ export const mapOrderAmountsFromUnitsToFill = (
   };
 };
 
+export function adjustTipsForPartialFills(
+  tips: ConsiderationItem[],
+  unitsToFill: BigNumberish,
+  totalSize: bigint,
+): ConsiderationItem[] {
+  const unitsToFillBn = BigInt(unitsToFill);
+
+  if (unitsToFillBn <= 0n) {
+    throw new Error("Units to fill must be greater than 0");
+  }
+
+  return tips.map((tip) => ({
+    ...tip,
+    startAmount: multiplyDivision(
+      tip.startAmount,
+      unitsToFillBn,
+      totalSize,
+    ).toString(),
+    endAmount: multiplyDivision(
+      tip.endAmount,
+      unitsToFillBn,
+      totalSize,
+    ).toString(),
+  }));
+}
+
 export const generateRandomSalt = (domain?: string) => {
   if (domain) {
     return toBeHex(