voucher saftey

cmd/cart/cart-grain.go

@@ -260,6 +260,10 @@ func (c *CartGrain) UpdateTotals() {
 	for _, voucher := range c.Vouchers {
 		if _, ok := voucher.AppliesTo(c); ok {
 			value := NewPriceFromIncVat(voucher.Value, 25)
+			if c.TotalPrice.IncVat <= value.IncVat {
+				// don't apply discounts to more than the total price
+				continue
+			}
 
 			c.TotalDiscount.Add(*value)
 			c.TotalPrice.Subtract(*value)

pkg/voucher/service.go

@@ -21,7 +21,6 @@ type Voucher struct {
 
 type Service struct {
 	// Add fields here
-
 }
 
 var ErrInvalidCode = errors.New("invalid vouchercode")