feat(utils): consolidate promotion utils + refactor + fixes (#6531)

packages/utils/src/totals/index.ts

@@ -7,6 +7,8 @@ import { BigNumber as BigNumberJs } from "bignumber.js"
 import { BigNumber } from "./big-number"
 import { toBigNumberJs } from "./to-big-number-js"
 
+export * from "./promotion"
+
 type GetLineItemTotalsContext = {
   includeTax?: boolean
   taxRate?: number | null

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

@@ -0,0 +1 @@
+export * from "./totals"

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

@@ -0,0 +1,58 @@
+import {
+  ApplicationMethodAllocation,
+  ApplicationMethodType,
+} from "../../promotion"
+
+function getPromotionValueForPercentage(promotion, lineItemTotal) {
+  return (promotion.value / 100) * lineItemTotal
+}
+
+function getPromotionValueForFixed(promotion, lineItemTotal, lineItemsTotal) {
+  if (promotion.allocation === ApplicationMethodAllocation.ACROSS) {
+    return (lineItemTotal / lineItemsTotal) * promotion.value
+  }
+
+  return promotion.value
+}
+
+export function getPromotionValue(promotion, lineItemTotal, lineItemsTotal) {
+  if (promotion.type === ApplicationMethodType.PERCENTAGE) {
+    return getPromotionValueForPercentage(promotion, lineItemTotal)
+  }
+
+  return getPromotionValueForFixed(promotion, lineItemTotal, lineItemsTotal)
+}
+
+export function getApplicableQuantity(lineItem, maxQuantity) {
+  if (maxQuantity && lineItem.quantity) {
+    return Math.min(lineItem.quantity, maxQuantity)
+  }
+
+  return lineItem.quantity
+}
+
+function getLineItemUnitPrice(lineItem) {
+  return lineItem.subtotal / lineItem.quantity
+}
+
+export function calculateAdjustmentAmountFromPromotion(
+  lineItem,
+  promotion,
+  lineItemsTotal = 0
+) {
+  const quantity = getApplicableQuantity(lineItem, promotion.max_quantity)
+  const lineItemTotal = getLineItemUnitPrice(lineItem) * quantity
+  const applicableTotal = lineItemTotal - promotion.applied_value
+
+  if (applicableTotal <= 0) {
+    return applicableTotal
+  }
+
+  const promotionValue = getPromotionValue(
+    promotion,
+    applicableTotal,
+    lineItemsTotal
+  )
+
+  return Math.min(promotionValue, applicableTotal)
+}