获取对象的随机方向以在迷宫内移动

Question

我正试图让一些游戏对象在迷宫中随机走动。我目前正常工作，对象可以向左/向右/向前。我遇到的问题是当有机会前进和左/右时总是选择左转或右转，他们从不选择前进，我无法弄清楚为什么......我在这里缺少什么？

public float speed;
public bool changed = false;
public bool forward, left, right;

protected Transform frontRaycast, leftRaycast, rightRaycast;

void Update(){
    if(!changed){
        forward = Physics2D.Linecast(transform.position, frontRaycast.position, 1 << LayerMask.NameToLayer("Wall"));
        left = Physics2D.Linecast(transform.position, leftRaycast.position, 1 << LayerMask.NameToLayer("Wall"));
        right = Physics2D.Linecast(transform.position, rightRaycast.position, 1 << LayerMask.NameToLayer("Wall"));

        List<int> possibleDirs = new List<int>();
        if(!forward){
            possibleDirs.Add(0);
        }
        if(!left){
            possibleDirs.Add(1);
        }
        if(!right){
            possibleDirs.Add(2);
        }
        int dir = 0;
        //Debug.Log(Random.Range(0, possibleDirs.Count));
        if(possibleDirs.Count > 0){
            dir = (int)possibleDirs[Random.Range(0, possibleDirs.Count)];
        }

        Debug.Log(dir);

        switch(dir){
            case 0:
                transform.Rotate(new Vector3(0,0,0));
                break;
            case 1:
                transform.Rotate(new Vector3(0,0,90));
                changed = true;
                Invoke("reset", 0.5f);
                break;
            case 2:
                transform.Rotate(new Vector3(0,0,-90));
                changed = true;
                Invoke("reset", 0.5f);
                break;
        }
    }
    transform.Translate(Vector2.right * Time.deltaTime * speed);
}

void reset(){
    changed = false;
}