private val toDirections = Map[RoadDirection, (RoadDirection, RoadDirection, RoadDirection, RoadDirection)](
    NoDirection -> (NoDirection, NoDirection, NoDirection, NoDirection),

    LeftDirection -> (LeftDirection, LeftDirection, RightDirection, RightDirection),
    RightDirection -> (LeftDirection, LeftDirection, RightDirection, RightDirection),
    TopDirection -> (BottomDirection, TopDirection, BottomDirection, TopDirection),
    BottomDirection -> (BottomDirection, TopDirection, TopDirection, TopDirection),

    LeftDirection + RightDirection -> (LeftDirection, LeftDirection, RightDirection, RightDirection),
    LeftDirection + BottomDirection -> (LeftDirection, LeftDirection, BottomDirection, TopDirection),
    LeftDirection + TopDirection -> (LeftDirection, TopDirection, RightDirection, TopDirection),
    RightDirection + BottomDirection -> (BottomDirection, LeftDirection, BottomDirection, RightDirection),
    RightDirection + TopDirection -> (BottomDirection, TopDirection, RightDirection, RightDirection),
    TopDirection + BottomDirection -> (BottomDirection, TopDirection, BottomDirection, TopDirection),


    TopDirection + BottomDirection + LeftDirection -> (LeftDirection + BottomDirection, LeftDirection + TopDirection,
      BottomDirection + RightDirection, TopDirection),
    TopDirection + BottomDirection + RightDirection -> (BottomDirection, LeftDirection + TopDirection,
      BottomDirection + RightDirection, TopDirection + RightDirection),
    TopDirection + LeftDirection + RightDirection -> (LeftDirection + BottomDirection, LeftDirection + TopDirection,
      RightDirection, TopDirection + RightDirection),
    BottomDirection + LeftDirection + RightDirection -> (LeftDirection + BottomDirection, LeftDirection,
      RightDirection + BottomDirection, TopDirection + RightDirection),

    new RoadDirection(true, true, true, true) -> (LeftDirection + BottomDirection, LeftDirection + TopDirection,
      RightDirection + BottomDirection, TopDirection + RightDirection)
  )