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_payment_completed.go

@@ -0,0 +1,37 @@
+package checkout
+
+import (
+	"fmt"
+	"time"
+
+	messages "git.k6n.net/go-cart-actor/proto/checkout"
+)
+
+// PaymentCompleted registers the completion of a payment for a checkout.
+func HandlePaymentCompleted(g *CheckoutGrain, m *messages.PaymentCompleted) error {
+	if m == nil {
+		return fmt.Errorf("PaymentCompleted: nil payload")
+	}
+	paymentId := m.PaymentId
+	payment, found := g.FindPayment(paymentId)
+
+	if !found {
+		return fmt.Errorf("PaymentCompleted: payment not found")
+	}
+
+	payment.ProcessorReference = m.ProcessorReference
+	payment.Status = PaymentStatusSuccess
+	payment.Amount = m.Amount
+	payment.Currency = m.Currency
+	payment.CompletedAt = &time.Time{}
+	if m.CompletedAt != nil {
+		*payment.CompletedAt = m.CompletedAt.AsTime()
+	} else {
+		*payment.CompletedAt = time.Now()
+	}
+
+	// Update checkout status
+	g.PaymentInProgress--
+
+	return nil
+}