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/checkout/mutation_confirmation_viewed.go

@@ -0,0 +1,26 @@
+package checkout
+
+import (
+	"fmt"
+	"time"
+
+	messages "git.k6n.net/go-cart-actor/proto/checkout"
+)
+
+func HandleConfirmationViewed(g *CheckoutGrain, m *messages.ConfirmationViewed) error {
+	if m == nil {
+		return fmt.Errorf("ConfirmationViewed: nil payload")
+	}
+
+	if g.Confirmation != nil {
+		g.Confirmation = &ConfirmationStatus{
+			ViewCount:    1,
+			LastViewedAt: time.Now(),
+		}
+	} else {
+		g.Confirmation.ViewCount++
+		g.Confirmation.LastViewedAt = time.Now()
+	}
+
+	return nil
+}