refactor/checkout (#8)

Co-authored-by: matst80 <mats.tornberg@gmail.com>
Reviewed-on: #8
Co-authored-by: Mats Törnberg <mats@tornberg.me>
Co-committed-by: Mats Törnberg <mats@tornberg.me>

pkg/cart/mutation_clear_cart.go

@@ -0,0 +1,26 @@
+package cart
+
+import (
+	"fmt"
+
+	messages "git.k6n.net/go-cart-actor/proto/cart"
+)
+
+func ClearCart(g *CartGrain, m *messages.ClearCartRequest) error {
+	if m == nil {
+		return fmt.Errorf("ClearCart: nil payload")
+	}
+	if g.CheckoutStatus != nil {
+		return fmt.Errorf("ClearCart: cart is in checkout")
+	}
+	// Clear items, vouchers, etc., but keep userId, etc.
+	g.Items = g.Items[:0]
+	g.Vouchers = g.Vouchers[:0]
+	g.Notifications = g.Notifications[:0]
+	g.OrderReference = ""
+	g.Processing = false
+
+	// g.InventoryReserved = false maybe should release inventory
+	g.UpdateTotals()
+	return nil
+}