feat: game lobby service

lobby/internal/domain/membership/status.go

@@ -0,0 +1,80 @@
+package membership
+
+// Status identifies one lifecycle state of a Game Lobby membership record.
+type Status string
+
+const (
+	// StatusActive reports that the member is a full participant and may
+	// send commands through Game Master.
+	StatusActive Status = "active"
+
+	// StatusRemoved reports that the member was removed post-start. The
+	// engine slot is deactivated; the race name reservation is preserved
+	// until the game finishes.
+	StatusRemoved Status = "removed"
+
+	// StatusBlocked reports that the member is blocked at the platform
+	// level. The engine slot is retained; commands are blocked.
+	StatusBlocked Status = "blocked"
+)
+
+// IsKnown reports whether status belongs to the frozen membership status
+// vocabulary.
+func (status Status) IsKnown() bool {
+	switch status {
+	case StatusActive, StatusRemoved, StatusBlocked:
+		return true
+	default:
+		return false
+	}
+}
+
+// IsTerminal reports whether status can no longer accept lifecycle
+// transitions.
+func (status Status) IsTerminal() bool {
+	switch status {
+	case StatusRemoved, StatusBlocked:
+		return true
+	default:
+		return false
+	}
+}
+
+// transitionKey stores one `(from, to)` pair in the allowed-transitions
+// table.
+type transitionKey struct {
+	from Status
+	to   Status
+}
+
+// allowedTransitions stores the set of permitted `(from, to)` status pairs.
+// It mirrors the state machine frozen in lobby/README.md Membership Model
+// section.
+var allowedTransitions = map[transitionKey]struct{}{
+	{StatusActive, StatusRemoved}: {},
+	{StatusActive, StatusBlocked}: {},
+}
+
+// AllowedTransitions returns a copy of the `(from, to)` allowed-transitions
+// table used by Transition. The returned map is safe to mutate.
+func AllowedTransitions() map[Status][]Status {
+	result := make(map[Status][]Status)
+	for key := range allowedTransitions {
+		result[key.from] = append(result[key.from], key.to)
+	}
+	return result
+}
+
+// Transition reports whether from may transition to next. The function
+// returns nil when the pair is permitted, and an *InvalidTransitionError
+// wrapping ErrInvalidTransition otherwise. It does not touch any store and
+// is safe to call from any layer.
+func Transition(from Status, next Status) error {
+	if !from.IsKnown() || !next.IsKnown() {
+		return &InvalidTransitionError{From: from, To: next}
+	}
+	if _, ok := allowedTransitions[transitionKey{from: from, to: next}]; !ok {
+		return &InvalidTransitionError{From: from, To: next}
+	}
+	return nil
+}