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_delivery.go

@@ -0,0 +1,55 @@
+package checkout
+
+import (
+	"fmt"
+
+	"git.k6n.net/go-cart-actor/pkg/cart"
+	messages "git.k6n.net/go-cart-actor/proto/checkout"
+)
+
+func asPickupPoint(p *messages.PickupPoint, deliveryId uint32) *PickupPoint {
+	if p == nil {
+		return nil
+	}
+	return &PickupPoint{
+		Id:      p.Id,
+		Name:    p.Name,
+		Address: p.Address,
+		City:    p.City,
+		Country: p.Country,
+		Zip:     p.Zip,
+	}
+}
+
+// HandleSetDelivery mutation
+// HandleSetDelivery mutation
+func HandleSetDelivery(g *CheckoutGrain, m *messages.SetDelivery) error {
+	if m == nil {
+		return fmt.Errorf("HandleSetDelivery: nil payload")
+	}
+	if m.Provider == "" {
+		return fmt.Errorf("HandleSetDelivery: missing provider")
+	}
+
+	// Check if delivery already exists, update or add
+	for _, d := range g.Deliveries {
+		if d.Provider == m.Provider {
+			// Update existing
+			d.Items = m.Items
+			d.PickupPoint = asPickupPoint(m.PickupPoint, d.Id)
+			return nil
+		}
+	}
+
+	// Add new delivery
+	g.lastDeliveryId++
+	delivery := &CheckoutDelivery{
+		Id:          g.lastDeliveryId,
+		Provider:    m.Provider,
+		Items:       m.Items,
+		PickupPoint: asPickupPoint(m.PickupPoint, g.lastDeliveryId),
+		Price:       *cart.NewPrice(), // Price might need calculation, but for now zero
+	}
+	g.Deliveries = append(g.Deliveries, delivery)
+	return nil
+}