add more payment related shit

pkg/cart/mutation_payment_completed.go

@@ -0,0 +1,32 @@
+package cart
+
+import (
+	"fmt"
+	"time"
+
+	messages "git.k6n.net/go-cart-actor/pkg/messages"
+)
+
+// PaymentStarted registers the beginning of a payment attempt for a cart.
+// It either upserts the payment entry (based on paymentId) or creates a new one,
+// marks the cart as having an in-progress payment, and recalculates the PaidInFull flag.
+func PaymentCompleted(grain *CartGrain, msg *messages.PaymentCompleted) error {
+	if msg == nil {
+		return fmt.Errorf("PaymentStarted: nil payload")
+	}
+	paymentId := msg.PaymentId
+	payment, found := grain.FindPayment(paymentId)
+	if !found {
+		return fmt.Errorf("PaymentStarted: payment not found")
+	}
+
+	payment.ProcessorReference = msg.ProcessorReference
+	payment.Status = PaymentStatusSuccess
+	payment.Amount = msg.Amount
+	payment.Currency = msg.Currency
+	payment.CompletedAt = asPointer(time.Now())
+
+	// maybe update cart status
+
+	return nil
+}