feat: game lobby service

lobby/internal/domain/membership/errors.go

@@ -0,0 +1,42 @@
+package membership
+
+import (
+	"errors"
+	"fmt"
+)
+
+// ErrNotFound reports that a membership record was requested but does not
+// exist in the store.
+var ErrNotFound = errors.New("membership not found")
+
+// ErrConflict reports that a membership mutation could not be applied
+// because the record changed concurrently or failed a compare-and-swap
+// guard.
+var ErrConflict = errors.New("membership conflict")
+
+// ErrInvalidTransition is the sentinel returned when Transition rejects a
+// `(from, to)` pair.
+var ErrInvalidTransition = errors.New("invalid membership status transition")
+
+// InvalidTransitionError stores the rejected `(from, to)` pair 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
+}
+
+// Error reports a human-readable summary of the rejected pair.
+func (err *InvalidTransitionError) Error() string {
+	return fmt.Sprintf(
+		"invalid membership status transition from %q to %q",
+		err.From, err.To,
+	)
+}
+
+// Unwrap returns ErrInvalidTransition so errors.Is recognizes the sentinel.
+func (err *InvalidTransitionError) Unwrap() error {
+	return ErrInvalidTransition
+}