class Guard : IUpdate
{
	private readonly Map _map;
	private readonly HashSet<(Vector2I, char)> _path = [];

	public char Direction { get; set; }

	public Vector2I Position { get; set; }

	public Guard(Map map)
	{
		_map = map;
		map.RegisterOnUpdate(this);
	}

	public bool? Step()
	{
		if (!_path.Add((Position, Direction)))
		{
			return null;
		}
		var test = NextPosition();
		if (!_map.IsValid(test))
		{
			return false;
		}
		else if (_map.IsOccupied(test))
		{
			Direction = Turn();
		}
		else
		{
			Position = test;
		}

		return true;
	}

	public void Update()
	{
		var tmpPosition = Position;
		if (Step() is not true)
		{
			_map.UnregisterOnUpdate(this);
		}
		else
		{
			_map.Move(tmpPosition, Position);
		}
	}

	private Vector2I NextPosition()
	{
		return Position + Program.ToVector(Direction);
	}

	private char Turn()
	{
		return Direction switch
		{
			'^' => '>',
			'>' => 'v',
			'v' => '<',
			'<' => '^',
			_ => throw new InvalidOperationException()
		};
	}
}