enum RuntimeSessionState { created, loading, active, disposing, disposed }

class RuntimeSession {
  RuntimeSession({required this.gameId}) : id = _nextId++;

  static int _nextId = 1;

  final int id;
  final String gameId;
  RuntimeSessionState _state = RuntimeSessionState.created;

  RuntimeSessionState get state => _state;

  bool get isLoading => _state == RuntimeSessionState.loading;

  bool get isActive => _state == RuntimeSessionState.active;

  bool get isDisposing => _state == RuntimeSessionState.disposing;

  bool get isDisposed => _state == RuntimeSessionState.disposed;

  bool get acceptsWork =>
      _state != RuntimeSessionState.disposing &&
      _state != RuntimeSessionState.disposed;

  void beginLoading() {
    _transition(
      RuntimeSessionState.loading,
      allowedFrom: const {RuntimeSessionState.created},
    );
  }

  void activate() {
    _transition(
      RuntimeSessionState.active,
      allowedFrom: const {
        RuntimeSessionState.created,
        RuntimeSessionState.loading,
      },
    );
  }

  void beginDisposing() {
    if (_state == RuntimeSessionState.disposed ||
        _state == RuntimeSessionState.disposing) {
      return;
    }
    _state = RuntimeSessionState.disposing;
  }

  void dispose() {
    _state = RuntimeSessionState.disposed;
  }

  bool accepts(int sessionId) => isActive && id == sessionId;

  bool acceptsWorkFor(int sessionId) => acceptsWork && id == sessionId;

  void _transition(
    RuntimeSessionState next, {
    required Set<RuntimeSessionState> allowedFrom,
  }) {
    if (_state == next) {
      return;
    }
    if (!allowedFrom.contains(_state)) {
      throw StateError('Invalid runtime session transition: $_state -> $next');
    }
    _state = next;
  }
}