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_add_item.go

@@ -7,7 +7,7 @@ import (
 	"log"
 	"time"
 
-	messages "git.k6n.net/go-cart-actor/pkg/messages"
+	cart_messages "git.k6n.net/go-cart-actor/proto/cart"
 	"google.golang.org/protobuf/types/known/timestamppb"
 )
 
@@ -26,7 +26,7 @@ import (
 // must keep this handler in sync.
 var ErrPaymentInProgress = errors.New("payment in progress")
 
-func (c *CartMutationContext) AddItem(g *CartGrain, m *messages.AddItem) error {
+func (c *CartMutationContext) AddItem(g *CartGrain, m *cart_messages.AddItem) error {
 	ctx := context.Background()
 	if m == nil {
 		return fmt.Errorf("AddItem: nil payload")
@@ -34,9 +34,6 @@ func (c *CartMutationContext) AddItem(g *CartGrain, m *messages.AddItem) error {
 	if m.Quantity < 1 {
 		return fmt.Errorf("AddItem: invalid quantity %d", m.Quantity)
 	}
-	if g.PaymentInProgress > 0 {
-		return ErrPaymentInProgress
-	}
 
 	// Merge with any existing item having same SKU and matching StoreId (including both nil).
 	for _, existing := range g.Items {