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fix(promotion): handle fixed discount type in buy-get promotions (#14939)
## What Fix buy-get promotions ignoring the fixed discount type. ## Why A merchant setting up "Buy 2, get $5 off the 3rd item" gets a $5 discount treated as 5,000% off instead. The engine ignores `application_method.type` and always runs the percentage formula, despite the promotion model and API supporting the `fixed` type for buy-get promotions. ## How Branch on `ApplicationMethodType.FIXED` in `applyPromotionToTargetItems` to apply the correct calculation per type, consistent with how `shipping-methods.ts` handles the same logic. Rename `applicablePercentage` to `promotionValue` to match sibling file naming (`shipping-methods.ts`, `line-items.ts`). Default fallback for missing `value` changed from `100` to `0` to align with sibling conventions. ## Testing Added 3 integration tests: basic fixed discount, cap at item price, multi-quantity application. All 89 existing compute-actions tests pass. ## Note The JSDoc examples in `service.ts` for `createPromotions` show buyget with `type: "fixed"` and no `value` field. These examples should be updated separately. Fixes #14934
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‎.changeset/fix-buyget-fixed-discount.md‎

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---
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"@medusajs/promotion": patch
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---
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fix(promotion): support fixed amount discount type in buy-get promotions

‎packages/modules/promotion/integration-tests/__tests__/services/promotion-module/compute-actions.spec.ts‎

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@@ -6003,6 +6003,269 @@ moduleIntegrationTestRunner({
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expect(JSON.parse(JSON.stringify(result))).toEqual([])
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})
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it("should compute fixed amount discount for buyget promotion", async () => {
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const context = {
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currency_code: "usd",
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customer: {
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customer_group: {
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id: "VIP",
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},
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},
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items: [
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{
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id: "item_cotton_tshirt",
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quantity: 1,
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subtotal: 500,
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original_total: 500,
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is_discountable: true,
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product_category: {
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id: "catg_tshirt",
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},
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product: {
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id: "prod_tshirt_1",
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},
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},
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{
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id: "item_cotton_sweater",
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quantity: 2,
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subtotal: 1000,
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original_total: 1000,
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is_discountable: true,
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product_category: {
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id: "catg_sweater",
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},
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product: {
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id: "prod_sweater_1",
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},
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},
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],
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}
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await createDefaultPromotion(service, {
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type: PromotionType.BUYGET,
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rules: [
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{
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attribute: "customer.customer_group.id",
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operator: "in",
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values: ["VIP", "top100"],
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},
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],
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application_method: {
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type: "fixed",
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target_type: "items",
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value: 200,
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allocation: "each",
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max_quantity: 1,
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apply_to_quantity: 1,
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buy_rules_min_quantity: 1,
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target_rules: [
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{
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attribute: "items.product_category.id",
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operator: "eq",
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values: ["catg_tshirt"],
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},
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],
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buy_rules: [
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{
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attribute: "items.product_category.id",
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operator: "eq",
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values: ["catg_sweater"],
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},
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],
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} as any,
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})
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const result = await service.computeActions(
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["PROMOTION_TEST"],
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context
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)
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expect(JSON.parse(JSON.stringify(result))).toEqual([
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{
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action: "addItemAdjustment",
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item_id: "item_cotton_tshirt",
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amount: 200,
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code: "PROMOTION_TEST",
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},
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])
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})
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it("should cap fixed discount at item price when value exceeds item price", async () => {
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const context = {
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currency_code: "usd",
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customer: {
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customer_group: {
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id: "VIP",
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},
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},
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items: [
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{
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id: "item_cotton_tshirt",
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quantity: 1,
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subtotal: 500,
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original_total: 500,
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is_discountable: true,
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product_category: {
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id: "catg_tshirt",
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},
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product: {
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id: "prod_tshirt_1",
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},
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},
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{
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id: "item_cotton_sweater",
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quantity: 2,
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subtotal: 1000,
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original_total: 1000,
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is_discountable: true,
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product_category: {
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id: "catg_sweater",
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},
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product: {
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id: "prod_sweater_1",
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},
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},
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],
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}
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await createDefaultPromotion(service, {
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type: PromotionType.BUYGET,
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rules: [
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{
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attribute: "customer.customer_group.id",
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operator: "in",
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values: ["VIP", "top100"],
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},
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],
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application_method: {
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type: "fixed",
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target_type: "items",
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value: 1000,
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allocation: "each",
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max_quantity: 1,
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apply_to_quantity: 1,
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buy_rules_min_quantity: 1,
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target_rules: [
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{
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attribute: "items.product_category.id",
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operator: "eq",
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values: ["catg_tshirt"],
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},
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],
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buy_rules: [
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{
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attribute: "items.product_category.id",
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operator: "eq",
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values: ["catg_sweater"],
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},
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],
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} as any,
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})
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const result = await service.computeActions(
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["PROMOTION_TEST"],
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context
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)
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// Fixed value 1000 exceeds item price 500, should be capped at 500
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expect(JSON.parse(JSON.stringify(result))).toEqual([
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{
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action: "addItemAdjustment",
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item_id: "item_cotton_tshirt",
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amount: 500,
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code: "PROMOTION_TEST",
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},
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])
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})
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it("should apply fixed discount per unit when apply_to_quantity > 1", async () => {
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const context = {
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currency_code: "usd",
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customer: {
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customer_group: {
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id: "VIP",
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},
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},
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items: [
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{
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id: "item_cotton_tshirt",
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quantity: 3,
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subtotal: 3000,
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original_total: 3000,
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is_discountable: true,
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product_category: {
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id: "catg_tshirt",
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},
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product: {
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id: "prod_tshirt_1",
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},
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},
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{
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id: "item_cotton_sweater",
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quantity: 2,
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subtotal: 1000,
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original_total: 1000,
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is_discountable: true,
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product_category: {
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id: "catg_sweater",
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},
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product: {
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id: "prod_sweater_1",
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},
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},
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],
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}
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await createDefaultPromotion(service, {
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type: PromotionType.BUYGET,
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rules: [
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{
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attribute: "customer.customer_group.id",
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operator: "in",
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values: ["VIP", "top100"],
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},
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],
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application_method: {
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type: "fixed",
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target_type: "items",
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value: 200,
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allocation: "each",
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max_quantity: 2,
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apply_to_quantity: 2,
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buy_rules_min_quantity: 1,
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target_rules: [
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{
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attribute: "items.product_category.id",
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operator: "eq",
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values: ["catg_tshirt"],
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},
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],
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buy_rules: [
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{
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attribute: "items.product_category.id",
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operator: "eq",
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values: ["catg_sweater"],
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},
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],
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} as any,
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})
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const result = await service.computeActions(
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["PROMOTION_TEST"],
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context
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)
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// Fixed value 200 per unit * 2 units = 400 total
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expect(JSON.parse(JSON.stringify(result))).toEqual([
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{
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action: "addItemAdjustment",
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item_id: "item_cotton_tshirt",
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amount: 400,
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code: "PROMOTION_TEST",
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},
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])
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})
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it("should compute actions for multiple items when conditions for target qty exceed one item", async () => {
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const context = {
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currency_code: "usd",

‎packages/modules/promotion/src/utils/compute-actions/buy-get.ts‎

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@@ -6,6 +6,7 @@ import {
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} from "@medusajs/framework/types"
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import {
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ApplicationMethodTargetType,
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ApplicationMethodType,
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ComputedActions,
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MathBN,
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MedusaError,
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const maximumApplyQuantity = MathBN.convert(
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promotion.application_method?.max_quantity ?? 1
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)
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const applicablePercentage = promotion.application_method?.value ?? 100
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const promotionValue = promotion.application_method?.value ?? 0
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return {
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minimumBuyQuantity,
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targetApplyQuantity,
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maximumApplyQuantity,
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applicablePercentage,
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promotionValue,
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}
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}
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minimumBuyQuantity: BigNumberInput
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targetApplyQuantity: BigNumberInput
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maximumApplyQuantity: BigNumberInput
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applicablePercentage: number
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promotionValue: number
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}
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type PromotionApplication = {
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Applies promotion to the target items selected by preparePromotionApplicationState.
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This function performs the application by:
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1. Calculating promotion amounts based on item prices and promotion percentage
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1. Calculating promotion amounts based on item prices and promotion value (percentage or fixed)
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2. Checking promotion budget limits to prevent overspending
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3. Updating promotional value tracking maps for cross-promotion coordination
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4. Accumulating total promotion amounts per item across all applications
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const multiplier = MathBN.min(targetItem.quantity, remainingQtyToApply)
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const pricePerUnit = MathBN.div(item.subtotal, item.quantity)
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const applicableAmount = MathBN.mult(pricePerUnit, multiplier)
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const amount = MathBN.mult(
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applicableAmount,
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applicationConfig.applicablePercentage
307-
).div(100)
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let amount
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if (promotion.application_method?.type === ApplicationMethodType.FIXED) {
308+
// Fixed: apply value per unit, capped at item price
309+
amount = MathBN.min(
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MathBN.mult(applicationConfig.promotionValue, multiplier),
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applicableAmount
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)
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} else {
314+
amount = MathBN.mult(
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applicableAmount,
316+
applicationConfig.promotionValue
317+
).div(100)
318+
}
308319

309320
if (MathBN.lte(amount, 0)) {
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continue

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