Fix after_cashback_amount_total to use the line total

src/__tests__/fixtures/price-getag.samples.ts

@@ -1,6 +1,23 @@
-import type { PriceItemDto } from '../../shared/types';
+import type { Coupon, PriceItemDto } from '../../shared/types';
 import { tax19percent } from './tax.samples';
 
+/**
+ * Attaches a coupon to every price component of a composite price, mirroring
+ * how coupons reach components (e.g. GetAG) in a journey. Useful for tests
+ * that exercise coupon/cashback behaviour on composite GetAG prices.
+ */
+export const withCouponOnComponents = (composite: PriceItemDto, coupon: Coupon): PriceItemDto =>
+  ({
+    ...composite,
+    _price: {
+      ...(composite._price as any),
+      price_components: (composite._price as any)?.price_components?.map((component: any) => ({
+        ...component,
+        _coupons: [coupon],
+      })),
+    },
+  }) as PriceItemDto;
+
 export const priceGetAG: PriceItemDto = {
   quantity: 1,
   product_id: 'prod-id#1',

src/__tests__/fixtures/pricing.results.ts

@@ -8340,8 +8340,8 @@ export const computedPriceWithFixedAmountCashbackCouponAndPriceMappings = {
       amount_tax: 1818,
       cashback_amount: 2000,
       cashback_amount_decimal: '20',
-      after_cashback_amount_total: 8000,
-      after_cashback_amount_total_decimal: '80',
+      after_cashback_amount_total: 18000,
+      after_cashback_amount_total_decimal: '180',
       currency: 'EUR',
       description: 'Winter Sale',
       cashback_period: '12',

src/computations/apply-discounts.ts

@@ -52,7 +52,10 @@ export const applyDiscounts = (
       priceItem?._price?.billing_period as BillingPeriod,
     );
 
-    afterCashbackAmountTotal = unitAmountGross.subtract(normalizedCashbackAmount);
+    // Deduct the cashback from the line total, not the per-unit gross.
+    const amountTotal = toDineroFromInteger(itemValues.amount_total!, currency);
+
+    afterCashbackAmountTotal = amountTotal.subtract(normalizedCashbackAmount);
 
     return {
       ...itemValues,

src/computations/pricing-getag.test.ts

@@ -1,4 +1,4 @@
-import type { PriceItem, PriceItemDto } from '@epilot/pricing-client';
+import type { CompositePriceItem, PriceItem, PriceItemDto } from '@epilot/pricing-client';
 import { describe, expect, it } from 'vitest';
 import {
   compositePriceGetAG,
@@ -8,7 +8,9 @@ import {
   priceGetAG,
   priceTieredFlatFeeGetAG,
   priceTieredVolumeGetAG,
+  withCouponOnComponents,
 } from '../__tests__/fixtures/price-getag.samples';
+import { percentageCashbackCoupon, percentageDiscountCoupon } from '../coupons/__tests__/coupon.fixtures';
 import { computeAggregatedAndPriceTotals } from './compute-totals';
 
 describe('GetAG - computeAggregatedAndPriceTotals', () => {
@@ -679,4 +681,52 @@ describe('GetAG - computeAggregatedAndPriceTotals', () => {
       });
     });
   });
+
+  describe('when a coupon is applied to GetAG components', () => {
+    describe('percentage cashback', () => {
+      it('does not produce a negative after-cashback total for work prices (regression)', () => {
+        const result = computeAggregatedAndPriceTotals([
+          withCouponOnComponents(compositePriceGetAG, percentageCashbackCoupon),
+        ]);
+
+        const components = (result.items?.[0] as CompositePriceItem)?.item_components;
+        const basePriceComponent = components?.[0];
+        const workPriceComponent = components?.[1];
+
+        // Base price component: amount_total === unit gross, so the value was already correct.
+        expect(basePriceComponent?.amount_total).toBe(1538);
+        expect(basePriceComponent?.cashback_amount).toBe(154);
+        expect(basePriceComponent?.after_cashback_amount_total).toBe(1525);
+
+        // Work price component: amount_total = per-unit gross × consumption.
+        // Previously after_cashback was computed from the tiny per-unit gross
+        // (≈ 24) minus the whole cashback, yielding a negative total (-177).
+        // It must now be derived from the line total instead: 24144 - 201 = 23943.
+        expect(workPriceComponent?.amount_total).toBe(24144);
+        expect(workPriceComponent?.cashback_amount).toBe(2414);
+        expect(workPriceComponent?.after_cashback_amount_total).toBe(23943);
+        expect(workPriceComponent?.after_cashback_amount_total).toBeGreaterThan(0);
+      });
+    });
+
+    describe('percentage discount', () => {
+      it('keeps before-discount totals above the discounted totals for GetAG components', () => {
+        const result = computeAggregatedAndPriceTotals([
+          withCouponOnComponents(compositePriceGetAG, percentageDiscountCoupon),
+        ]);
+
+        const components = (result.items?.[0] as CompositePriceItem)?.item_components;
+        const workPriceComponent = components?.[1];
+
+        // before_discount (24144) stays above the discounted total (18108).
+        expect(workPriceComponent?.before_discount_amount_total).toBe(24144);
+        expect(workPriceComponent?.amount_total).toBe(18108);
+        expect(workPriceComponent?.discount_amount).toBe(6036);
+
+        const recurrence = result.total_details?.breakdown?.recurrences?.[0];
+        expect(recurrence?.before_discount_amount_total).toBe(25682);
+        expect(recurrence?.amount_total).toBe(19262);
+      });
+    });
+  });
 });