"""




class SnakeBodySegment:
    """Finally, we need an Agent for the snake's body segments. 
    SnakeBodySegment doesn't have ``play_turn`` or ``handle_keystroke`` methods because
    it never does anything on its own. It only moves when the SnakeHead, or the previous
    segment, tells it to move. 

    Arguments: 
        segment_id (int): Keeps track of how far back this segment is from the head.
            This is used to give the segment a unique name, and also to keep track 
            of how many points the player earns for eating the next apple. 
        position (int, int): The initial position.

    Attributes:
        character: '*'
        next_segment: Initially ``None``, this is a reference to a SnakeBodySegment
            when this segment is not the last one in the snake's body.
            
    """
    character = '*'
    next_segment = None

    def __init__(self, segment_id, position):
        self.segment_id = segment_id
        self.name = f"Snake body segment {segment_id}"
        self.position = position

    def move(self, new_position, game, growing=False):
        """When SnakeHead moves, it sets off a chain reaction, moving all its 
        body segments. Whenever the head or a body segment has another segment 
        (``next_segment``), it calls that segment's ``move`` method.

        This method updates the SnakeBodySegment's position. Then, if 
        ``self.next_segment`` is not None, calls that segment's ``move`` method. 
        If there is no next segment and ``growing`` is True, then we set
        ``self.next_segment`` to a new SnakeBodySegment in this segment's old
        position, and update the game's score.

        Arguments: 
            new_position (int, int): The new position.
            game (Game): A reference to the current game.
            growing (bool): (Default False) When True, the snake needs to 
                add a new segment. 
        """
        old_position = self.position
        self.position = new_position
        if self.next_segment:
            self.next_segment.move(old_position, game, growing=growing)
        elif growing:
            self.next_segment = SnakeBodySegment(self.segment_id + 1, old_position)
            game.add_agent(self.next_segment)
            game.state['score'] += self.segment_id + 1