all the refactor

pkg/cart/mutation_add_item.go

@@ -98,12 +98,14 @@ func (c *CartMutationContext) AddItem(g *CartGrain, m *cart_messages.AddItem) er
 	defer g.mu.Unlock()
 
 	g.lastItemId++
-	taxRate := float32(25.0)
+	// m.Tax is the rate in basis points (2500 = 25%, 1250 = 12.5%) — the single
+	// platform scale; flows straight through, no conversion.
+	rateBp := 2500
 	if m.Tax > 0 {
-		taxRate = float32(int(m.Tax) / 100)
+		rateBp = int(m.Tax)
 	}
 
-	pricePerItem := NewPriceFromIncVat(m.Price, taxRate)
+	pricePerItem := NewPriceFromIncVat(m.Price, rateBp)
 
 	needsReservation := true
 	if m.ReservationEndTime != nil {
@@ -115,7 +117,7 @@ func (c *CartMutationContext) AddItem(g *CartGrain, m *cart_messages.AddItem) er
 		ItemId:   uint32(m.ItemId),
 		Quantity: uint16(m.Quantity),
 		Sku:      m.Sku,
-		Tax:      int(taxRate * 100),
+		Tax:      rateBp,
 		Meta: &ItemMeta{
 			Name:       m.Name,
 			Image:      m.Image,
@@ -139,7 +141,7 @@ func (c *CartMutationContext) AddItem(g *CartGrain, m *cart_messages.AddItem) er
 		Stock:      uint16(m.Stock),
 		Disclaimer: m.Disclaimer,
 
-		OrgPrice:    getOrgPrice(m.OrgPrice, taxRate),
+		OrgPrice:    getOrgPrice(m.OrgPrice, rateBp),
 		ArticleType: m.ArticleType,
 
 		StoreId: m.StoreId,
@@ -167,9 +169,9 @@ func (c *CartMutationContext) AddItem(g *CartGrain, m *cart_messages.AddItem) er
 	return nil
 }
 
-func getOrgPrice(orgPrice int64, taxRate float32) *Price {
+func getOrgPrice(orgPrice int64, rateBp int) *Price {
 	if orgPrice <= 0 {
 		return nil
 	}
-	return NewPriceFromIncVat(orgPrice, taxRate)
+	return NewPriceFromIncVat(orgPrice, rateBp)
 }