link user

pkg/promotions/apply.go

@@ -31,7 +31,7 @@ type Effect interface {
 	// Apply mutates the cart for a qualifying action and returns the discount it
 	// took (nil for non-monetary effects such as free shipping) plus whether
 	// anything took effect worth recording.
-	Apply(g *cart.CartGrain, rule PromotionRule, a Action) (discount *cart.Price, applied bool)
+	Apply(g *cart.CartGrain, rule PromotionRule, a Action) (discount *cart.Price, itemIds []uint32, applied bool)
 	// Progress reports how far the cart is from (further) unlocking this action,
 	// as an open key/value payload. qualified says whether the owning rule
 	// currently applies, letting the effect distinguish "remaining to unlock"
@@ -77,8 +77,9 @@ func (s *PromotionService) ApplyResults(g *cart.CartGrain, results []EvaluationR
 			}
 			recorded := false
 			if res.Applicable {
-				if discount, applied := eff.Apply(g, res.Rule, a); applied {
+				if discount, itemIds, applied := eff.Apply(g, res.Rule, a); applied {
 					entry.Discount = discount
+					entry.ItemIds = itemIds
 					recorded = true
 				}
 			}
@@ -111,9 +112,9 @@ type percentageDiscountEffect struct{}
 
 func (percentageDiscountEffect) Type() ActionType { return ActionPercentageDiscount }
 
-func (percentageDiscountEffect) Apply(g *cart.CartGrain, _ PromotionRule, a Action) (*cart.Price, bool) {
+func (percentageDiscountEffect) Apply(g *cart.CartGrain, _ PromotionRule, a Action) (*cart.Price, []uint32, bool) {
 	d := applyPercentageDiscount(g, percentFromValue(a.Value))
-	return d, d != nil
+	return d, nil, d != nil
 }
 
 func (percentageDiscountEffect) Progress(s *PromotionService, rule PromotionRule, a Action, ctx *PromotionEvalContext, qualified bool) (map[string]any, bool) {
@@ -129,8 +130,8 @@ type freeShippingEffect struct{}
 
 func (freeShippingEffect) Type() ActionType { return ActionFreeShipping }
 
-func (freeShippingEffect) Apply(_ *cart.CartGrain, _ PromotionRule, _ Action) (*cart.Price, bool) {
-	return nil, true
+func (freeShippingEffect) Apply(_ *cart.CartGrain, _ PromotionRule, _ Action) (*cart.Price, []uint32, bool) {
+	return nil, nil, true
 }
 
 func (freeShippingEffect) Progress(s *PromotionService, rule PromotionRule, a Action, ctx *PromotionEvalContext, qualified bool) (map[string]any, bool) {
@@ -148,9 +149,9 @@ type tieredDiscountEffect struct{}
 
 func (tieredDiscountEffect) Type() ActionType { return ActionTieredDiscount }
 
-func (tieredDiscountEffect) Apply(g *cart.CartGrain, _ PromotionRule, a Action) (*cart.Price, bool) {
+func (tieredDiscountEffect) Apply(g *cart.CartGrain, _ PromotionRule, a Action) (*cart.Price, []uint32, bool) {
 	d := applyTieredDiscount(g, a)
-	return d, d != nil
+	return d, nil, d != nil
 }
 
 func (tieredDiscountEffect) Progress(s *PromotionService, rule PromotionRule, a Action, ctx *PromotionEvalContext, qualified bool) (map[string]any, bool) {
@@ -387,7 +388,7 @@ type unitItem struct {
 	price money.Cents
 }
 
-func (buyXGetYEffect) Apply(g *cart.CartGrain, rule PromotionRule, a Action) (*cart.Price, bool) {
+func (buyXGetYEffect) Apply(g *cart.CartGrain, rule PromotionRule, a Action) (*cart.Price, []uint32, bool) {
 	config := a.Config
 	buy := int(firstNum(config, "buy"))
 	if buy <= 0 {
@@ -416,7 +417,7 @@ func (buyXGetYEffect) Apply(g *cart.CartGrain, rule PromotionRule, a Action) (*c
 	n := len(units)
 	numFree := (n / (buy + get)) * get
 	if numFree <= 0 {
-		return nil, false
+		return nil, nil, false
 	}
 
 	// Sort units by price ascending so we discount the cheapest ones
@@ -431,13 +432,15 @@ func (buyXGetYEffect) Apply(g *cart.CartGrain, rule PromotionRule, a Action) (*c
 	})
 
 	totalDiscount := cart.NewPrice()
+	affectedMap := make(map[uint32]bool)
 	for i := 0; i < numFree; i++ {
 		unitDiscount := scalePrice(&units[i].item.Price, discount)
 		totalDiscount.Add(*unitDiscount)
+		affectedMap[units[i].item.Id] = true
 	}
 
 	if totalDiscount.IncVat <= 0 {
-		return nil, false
+		return nil, nil, false
 	}
 	// Never discount below zero.
 	if totalDiscount.IncVat > g.TotalPrice.IncVat {
@@ -445,7 +448,14 @@ func (buyXGetYEffect) Apply(g *cart.CartGrain, rule PromotionRule, a Action) (*c
 	}
 	g.TotalDiscount.Add(*totalDiscount)
 	g.TotalPrice.Subtract(*totalDiscount)
-	return totalDiscount, true
+
+	var itemIds []uint32
+	for id := range affectedMap {
+		itemIds = append(itemIds, id)
+	}
+	slices.Sort(itemIds)
+
+	return totalDiscount, itemIds, true
 }
 
 func (buyXGetYEffect) Progress(s *PromotionService, rule PromotionRule, a Action, ctx *PromotionEvalContext, qualified bool) (map[string]any, bool) {
@@ -460,9 +470,9 @@ type bundleDiscountEffect struct{}
 
 func (bundleDiscountEffect) Type() ActionType { return ActionBundleDiscount }
 
-func (bundleDiscountEffect) Apply(g *cart.CartGrain, _ PromotionRule, a Action) (*cart.Price, bool) {
+func (bundleDiscountEffect) Apply(g *cart.CartGrain, _ PromotionRule, a Action) (*cart.Price, []uint32, bool) {
 	if a.BundleConfig == nil {
-		return nil, false
+		return nil, nil, false
 	}
 
 	// 1. Represent all cart items as individual units
@@ -545,10 +555,11 @@ func (bundleDiscountEffect) Apply(g *cart.CartGrain, _ PromotionRule, a Action)
 	}
 
 	if len(formedBundles) == 0 {
-		return nil, false
+		return nil, nil, false
 	}
 
 	totalDiscount := cart.NewPrice()
+	affectedMap := make(map[uint32]bool)
 	for _, bundle := range formedBundles {
 		// Calculate the original bundle price
 		bundlePrice := cart.NewPrice()
@@ -579,11 +590,14 @@ func (bundleDiscountEffect) Apply(g *cart.CartGrain, _ PromotionRule, a Action)
 
 		if bundleDiscount != nil && bundleDiscount.IncVat > 0 {
 			totalDiscount.Add(*bundleDiscount)
+			for _, item := range bundle {
+				affectedMap[item.Id] = true
+			}
 		}
 	}
 
 	if totalDiscount.IncVat <= 0 {
-		return nil, false
+		return nil, nil, false
 	}
 	// Never discount below zero.
 	if totalDiscount.IncVat > g.TotalPrice.IncVat {
@@ -591,7 +605,14 @@ func (bundleDiscountEffect) Apply(g *cart.CartGrain, _ PromotionRule, a Action)
 	}
 	g.TotalDiscount.Add(*totalDiscount)
 	g.TotalPrice.Subtract(*totalDiscount)
-	return totalDiscount, true
+
+	var itemIds []uint32
+	for id := range affectedMap {
+		itemIds = append(itemIds, id)
+	}
+	slices.Sort(itemIds)
+
+	return totalDiscount, itemIds, true
 }
 
 func (bundleDiscountEffect) Progress(s *PromotionService, rule PromotionRule, a Action, ctx *PromotionEvalContext, qualified bool) (map[string]any, bool) {

pkg/promotions/apply_test.go

@@ -184,6 +184,13 @@ func TestBuyXGetYEffect(t *testing.T) {
 	if got := g.TotalPrice.IncVat; got != 2000 {
 		t.Errorf("total price = %d, want 2000", got)
 	}
+	if len(g.AppliedPromotions) != 1 {
+		t.Fatalf("expected 1 applied promotion, got %d", len(g.AppliedPromotions))
+	}
+	itemIds := g.AppliedPromotions[0].ItemIds
+	if len(itemIds) != 1 || itemIds[0] != 1 {
+		t.Errorf("expected affected itemIds [1], got %v", itemIds)
+	}
 }
 
 func TestBundleDiscountEffect(t *testing.T) {
@@ -247,4 +254,11 @@ func TestBundleDiscountEffect(t *testing.T) {
 	if got := g.TotalPrice.IncVat; got != 4000 {
 		t.Errorf("total price = %d, want 4000", got)
 	}
+	if len(g.AppliedPromotions) != 1 {
+		t.Fatalf("expected 1 applied promotion, got %d", len(g.AppliedPromotions))
+	}
+	itemIds := g.AppliedPromotions[0].ItemIds
+	if len(itemIds) != 2 || itemIds[0] != 1 || itemIds[1] != 2 {
+		t.Errorf("expected affected itemIds [1, 2], got %v", itemIds)
+	}
 }