package checkout

import (
	"fmt"

	messages "git.k6n.net/go-cart-actor/proto/checkout"
)

// mutation_order_created.go
//
// Registers the OrderCreated mutation.
//
// This mutation represents the completion (or state transition) of an order
// initiated earlier via InitializeCheckout / external processing.
// It finalizes (or updates) the checkout's order metadata.
//
// Behavior:
//   - Validates payload non-nil and OrderId not empty.
//   - Sets Status from payload.Status.
//   - Sets OrderId if not already set.
//   - Does NOT adjust monetary totals.
//
// Notes / Future Extensions:
//   - If multiple order completion events can arrive (e.g., retries / webhook
//     replays), this handler is idempotent: it simply overwrites fields.
//   - If you need to guard against conflicting order IDs, add a check:
//     if g.OrderId != "" && g.OrderId != m.OrderId { ... }
//   - Add audit logging or metrics here if required.
//
// Concurrency:
//   - Relies on the higher-level guarantee that Apply() calls are serialized
//     per grain. If out-of-order events are possible, embed versioning or
//     timestamps in the mutation and compare before applying changes.

func HandleOrderCreated(g *CheckoutGrain, m *messages.OrderCreated) error {
	if m == nil {
		return fmt.Errorf("HandleOrderCreated: nil payload")
	}
	if m.OrderId == "" {
		return fmt.Errorf("OrderCreated: missing orderId")
	}
	if g.OrderId == nil {
		g.OrderId = &m.OrderId
	} else if *g.OrderId != m.OrderId {
		return fmt.Errorf("OrderCreated: conflicting order ID")
	}

	return nil
}