feat: game lobby service

lobby/internal/domain/game/errors.go

@@ -0,0 +1,44 @@
+package game
+
+import (
+	"errors"
+	"fmt"
+)
+
+// ErrNotFound reports that a game record was requested but does not exist
+// in the store.
+var ErrNotFound = errors.New("game not found")
+
+// ErrConflict reports that a game mutation could not be applied because the
+// record changed concurrently or failed a compare-and-swap guard.
+var ErrConflict = errors.New("game conflict")
+
+// ErrInvalidTransition is the sentinel returned when Transition rejects a
+// `(from, to, trigger)` triplet.
+var ErrInvalidTransition = errors.New("invalid game status transition")
+
+// InvalidTransitionError stores the rejected `(from, to, trigger)` triplet
+// and wraps ErrInvalidTransition so callers can match it with errors.Is.
+type InvalidTransitionError struct {
+	// From stores the source status that was attempted to leave.
+	From Status
+
+	// To stores the destination status that was attempted to enter.
+	To Status
+
+	// Trigger stores the transition trigger that was attempted.
+	Trigger Trigger
+}
+
+// Error reports a human-readable summary of the rejected triplet.
+func (err *InvalidTransitionError) Error() string {
+	return fmt.Sprintf(
+		"invalid game status transition from %q to %q with trigger %q",
+		err.From, err.To, err.Trigger,
+	)
+}
+
+// Unwrap returns ErrInvalidTransition so errors.Is recognizes the sentinel.
+func (err *InvalidTransitionError) Unwrap() error {
+	return ErrInvalidTransition
+}