all the refactor

internal/ucp/checkout.go

@@ -15,6 +15,7 @@ import (
 	"git.k6n.net/mats/go-cart-actor/pkg/cart"
 	profilePkg "git.k6n.net/mats/go-cart-actor/pkg/profile"
 	checkoutMessages "git.k6n.net/mats/go-cart-actor/proto/checkout"
+	"git.k6n.net/mats/platform/money"
 	"google.golang.org/protobuf/types/known/anypb"
 	"google.golang.org/protobuf/types/known/timestamppb"
 )
@@ -447,15 +448,15 @@ type orderLine struct {
 	Reference string `json:"reference"`
 	Sku       string `json:"sku"`
 	Name      string `json:"name"`
-	Quantity  int32  `json:"quantity"`
-	UnitPrice int64  `json:"unitPrice"`
-	TaxRate   int32  `json:"taxRate"`
+	Quantity  int32       `json:"quantity"`
+	UnitPrice money.Cents `json:"unitPrice"`
+	TaxRate   int32       `json:"taxRate"`
 }
 
 type orderPayment struct {
-	Provider  string `json:"provider"`
-	Reference string `json:"reference"`
-	Amount    int64  `json:"amount"`
+	Provider  string      `json:"provider"`
+	Reference string      `json:"reference"`
+	Amount    money.Cents `json:"amount"`
 }
 
 // CreateOrder implements OrderApplier. It builds a from-checkout request from
@@ -476,10 +477,10 @@ func (c *OrderHTTPClient) CreateOrder(ctx context.Context, checkoutID uint64, g
 	}
 
 	// Compute total from cart items + deliveries.
-	var totalAmount int64
+	var totalAmount money.Cents
 	lines := buildOrderLines(g)
 	for _, l := range lines {
-		totalAmount += l.UnitPrice * int64(l.Quantity)
+		totalAmount += l.UnitPrice.Mul(int64(l.Quantity))
 	}
 
 	req := fromCheckoutReq{
@@ -554,8 +555,9 @@ func buildOrderLines(g *checkout.CheckoutGrain) []orderLine {
 			Name:      name,
 			Quantity:  int32(it.Quantity),
 			UnitPrice: it.Price.IncVat,
-			// CartItem.Tax is percentage x 100 (e.g. 2500 = 25.00%). Convert to raw percent (25).
-			TaxRate:   int32(it.Tax / 100),
+			// CartItem.Tax and OrderLine.TaxRate share the platform basis-point scale
+			// (2500 = 25%), so the rate passes through unchanged.
+			TaxRate:   int32(it.Tax),
 		})
 	}
 	for _, d := range g.Deliveries {
@@ -568,7 +570,7 @@ func buildOrderLines(g *checkout.CheckoutGrain) []orderLine {
 			Name:      "Delivery",
 			Quantity:  1,
 			UnitPrice: d.Price.IncVat,
-			TaxRate:   25,
+			TaxRate:   2500, // 25% in basis points
 		})
 	}
 	return lines
@@ -672,7 +674,7 @@ func checkoutGrainToResponse(id string, g *checkout.CheckoutGrain) CheckoutRespo
 		resp.Payments = append(resp.Payments, PaymentResponse{
 			Id:       p.PaymentId,
 			Provider: p.Provider,
-			Amount:   p.Amount,
+			Amount:   money.Cents(p.Amount),
 			Currency: p.Currency,
 			Status:   string(p.Status),
 		})