all the refactor

cmd/checkout/order_create.go

@@ -43,21 +43,29 @@ func buildOrderLinesFromGrain(grain *checkout.CheckoutGrain) []OrderLine {
 		if it == nil {
 			continue
 		}
+		// Carry the per-item store as the inventory commit location; empty when
+		// no store (commit then falls back to the order country / central stock).
+		location := ""
+		if it.StoreId != nil {
+			location = *it.StoreId
+		}
 		lines = append(lines, OrderLine{
 			Reference: it.Sku,
 			Sku:       it.Sku,
 			Name:      it.Meta.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),
+			UnitPrice: it.Price.IncVat.Int64(),
+			// CartItem.Tax and OrderLine.TaxRate share the platform basis-point scale
+			// (2500 = 25%), so the rate passes through unchanged.
+			TaxRate:   int32(it.Tax),
+			Location:  location,
 		})
 	}
 	for _, d := range grain.Deliveries {
 		if d == nil {
 			continue
 		}
-		unitPrice := d.Price.IncVat
+		unitPrice := d.Price.IncVat.Int64()
 		if hasFreeShipping {
 			unitPrice = 0
 		}
@@ -70,7 +78,7 @@ func buildOrderLinesFromGrain(grain *checkout.CheckoutGrain) []OrderLine {
 			Name:      "Delivery",
 			Quantity:  1,
 			UnitPrice: unitPrice,
-			TaxRate:   25,
+			TaxRate:   2500, // 25% in basis points
 		})
 	}
 
@@ -82,7 +90,7 @@ func buildOrderLinesFromGrain(grain *checkout.CheckoutGrain) []OrderLine {
 			}
 			discountVal := int64(0)
 			if ap.Discount != nil {
-				discountVal = ap.Discount.IncVat
+				discountVal = ap.Discount.IncVat.Int64()
 			}
 			if discountVal <= 0 {
 				continue
@@ -93,7 +101,7 @@ func buildOrderLinesFromGrain(grain *checkout.CheckoutGrain) []OrderLine {
 				Name:      "Promotion: " + ap.Name,
 				Quantity:  1,
 				UnitPrice: -discountVal,
-				TaxRate:   25, // default standard tax rate for promotion discount
+				TaxRate:   2500, // default standard tax rate (25%) in basis points
 			})
 		}
 	}