cart and checkout

pkg/promotions/eval.go

@@ -42,6 +42,7 @@ type PromotionEvalContext struct {
 	CustomerLifetimeValue float64
 	OrderCount            int
 	Now                   time.Time
+	CouponCodes           []string
 }
 
 // ContextOption allows customization of fields when building a PromotionEvalContext.
@@ -67,6 +68,11 @@ func WithNow(t time.Time) ContextOption {
 	return func(c *PromotionEvalContext) { c.Now = t }
 }
 
+// WithCouponCodes sets active coupon codes.
+func WithCouponCodes(codes []string) ContextOption {
+	return func(c *PromotionEvalContext) { c.CouponCodes = codes }
+}
+
 // NewContextFromCart builds a PromotionEvalContext from a CartGrain and optional metadata.
 func NewContextFromCart(g *cart.CartGrain, opts ...ContextOption) *PromotionEvalContext {
 	ctx := &PromotionEvalContext{
@@ -74,6 +80,7 @@ func NewContextFromCart(g *cart.CartGrain, opts ...ContextOption) *PromotionEval
 		CartTotalIncVat:   0,
 		TotalItemQuantity: 0,
 		Now:               time.Now(),
+		CouponCodes:       make([]string, 0),
 	}
 	if g.TotalPrice != nil {
 		ctx.CartTotalIncVat = g.TotalPrice.IncVat
@@ -91,6 +98,9 @@ func NewContextFromCart(g *cart.CartGrain, opts ...ContextOption) *PromotionEval
 		})
 		ctx.TotalItemQuantity += uint32(it.Quantity)
 	}
+	for _, v := range g.Vouchers {
+		ctx.CouponCodes = append(ctx.CouponCodes, v.Code)
+	}
 	for _, o := range opts {
 		o(ctx)
 	}
@@ -106,18 +116,29 @@ type PromotionService struct {
 	// even one that has already applied (e.g. a tiered discount at 5% pointing at
 	// the next 9% tier). Register a new Effect to add a new action type.
 	effects map[ActionType]Effect
+	// DefaultTaxProvider provides the VAT rate used when constructing synthetic
+	// carts for stateless evaluation and preview. When nil, falls back to 25 %.
+	DefaultTaxProvider cart.TaxProvider
 }
 
 // NewPromotionService constructs a PromotionService with an optional tracer and
 // the built-in effect handlers.
-func NewPromotionService(t Tracer) *PromotionService {
+// NewPromotionService constructs a PromotionService with an optional tracer.
+// When tp is non-nil, it is used as DefaultTaxProvider for synthetic cart
+// construction (stateless evaluation, preview); otherwise the service falls
+// back to 25 % VAT.
+func NewPromotionService(t Tracer, tp ...cart.TaxProvider) *PromotionService {
 	if t == nil {
 		t = NoopTracer{}
 	}
-	return &PromotionService{
+	s := &PromotionService{
 		tracer:  t,
 		effects: defaultEffects(),
 	}
+	if len(tp) > 0 && tp[0] != nil {
+		s.DefaultTaxProvider = tp[0]
+	}
+	return s
 }
 
 // RegisterEffect adds (or overrides) the handler for an action type, so new
@@ -360,11 +381,22 @@ func evaluateBaseCondition(b BaseCondition, ctx *PromotionEvalContext) bool {
 		return evalDayOfWeek(ctx.Now, b)
 	case CondTimeOfDay:
 		return evalTimeOfDay(ctx.Now, b)
+	case CondCouponCode:
+		return evalAnyCouponMatch(ctx.CouponCodes, b)
 	default:
 		return false
 	}
 }
 
+func evalAnyCouponMatch(codes []string, b BaseCondition) bool {
+	for _, code := range codes {
+		if evalStringCompare(code, b) {
+			return true
+		}
+	}
+	return false
+}
+
 func evalAnyItemMatch(pred func(PromotionItem) bool, b BaseCondition, ctx *PromotionEvalContext) bool {
 	if slices.ContainsFunc(ctx.Items, pred) {
 		return true