package {
    import flash.display.Sprite;
 
    //(具有)转向(行为的)机车
    public class SteeredVehicle extends Vehicle {
        private var _maxForce:Number=1;//最大转向力
        private var _steeringForce:Vector2D;//转向速度
	private var _arrivalThreshold:Number=100;//到达行为的距离阈值(小于这个距离将减速)

        public function SteeredVehicle(color:uint=0x000000) {
	    _color=color
            _steeringForce = new Vector2D();
            super();
        }
        public function set maxForce(value:Number):void {
            _maxForce=value;
        }
        public function get maxForce():Number {
            return _maxForce;
        }
         
	public function set arriveThreshold(value: Number):void {
	    _arrivalThreshold=value;
	}
	 
	public function get arriveThreshold():Number {
	    return _arrivalThreshold;
	}

        override public function update():void {
            _steeringForce.truncate(_maxForce);//限制为最大转向速度，以避免出现突然的大转身
            _steeringForce=_steeringForce.divide(_mass);//惯性的体现
            _velocity=_velocity.add(_steeringForce);
            _steeringForce = new Vector2D();
            super.update();
        }
	//寻找(Seek)行为
	public function seek(target: Vector2D):void {
	    var desiredVelocity:Vector2D=target.subtract(_position);
	    desiredVelocity.normalize();
	    desiredVelocity=desiredVelocity.multiply(_maxSpeed);//注：这里的_maxSpeed是从父类继承得来的
	    var force:Vector2D=desiredVelocity.subtract(_velocity);
	    _steeringForce=_steeringForce.add(force);
	}

	//避开(flee)行为
	public function flee(target: Vector2D):void {
	    var desiredVelocity:Vector2D=target.subtract(_position);
	    desiredVelocity.normalize();
	    desiredVelocity=desiredVelocity.multiply(_maxSpeed);
	    var force:Vector2D=desiredVelocity.subtract(_velocity);
	    _steeringForce=_steeringForce.subtract(force);//这是唯一与seek行为不同的地方，一句话解释：既然发现了目标，那就调头就跑吧！
	}
    
	//到达(arrive)行为
	public function arrive(target: Vector2D):void {
	    var desiredVelocity:Vector2D=target.subtract(_position);
	    desiredVelocity.normalize();
	    var dist:Number=_position.dist(target);
	    if (dist>_arrivalThreshold) {
			desiredVelocity=desiredVelocity.multiply(_maxSpeed);
	    } else {
			desiredVelocity=desiredVelocity.multiply(_maxSpeed*dist/_arrivalThreshold);
	    }
	    var force:Vector2D=desiredVelocity.subtract(_velocity);
		    _steeringForce=_steeringForce.add(force);
	}

	//追捕(pursue)行为
	public function pursue(target:Vehicle):void {
	    var lookAheadTime:Number=position.dist(target.position)/_maxSpeed;//假如目标不动，追捕者开足马力赶过去的话，计算需要多少时间
	    var predictedTarget:Vector2D=target.position.add(target.velocity.multiply(lookAheadTime));
	    seek(predictedTarget);
	}

	//躲避(evade)行为
	public function evade(target: Vehicle):void {
	    var lookAheadTime:Number=position.dist(target.position)/_maxSpeed;
	    var predictedTarget:Vector2D=target.position.add(target.velocity.multiply(lookAheadTime));
	    flee(predictedTarget);//仅仅只是这里改变了而已
	}
    
	private var _wanderAngle:Number=0;
	private var _wanderDistance:Number=10;
	private var _wanderRadius:Number=5;
	private var _wanderRange:Number=1;
	 
	//漫游
	public function wander():void {
	    var center:Vector2D=velocity.clone().normalize().multiply(_wanderDistance);
	    var offset:Vector2D=new Vector2D(0);
	    offset.length=_wanderRadius;
	    offset.angle=_wanderAngle;
	    _wanderAngle+=(Math.random()-0.5)*_wanderRange;
	    var force:Vector2D=center.add(offset);
	    _steeringForce=_steeringForce.add(force);
	}
	 
	public function set wanderDistance(value:Number):void {
	    _wanderDistance=value;
	}
	 
	public function get wanderDistance():Number {
	    return _wanderDistance;
	}
	 
	public function set wanderRadius(value:Number):void {
	    _wanderRadius=value;
	}
	 
	public function get wanderRadius():Number {
	    return _wanderRadius;
	}
	 
	public function set wanderRange(value:Number):void {
	    _wanderRange=value;
	}
	 
	public function get wanderRange():Number {
	    return _wanderRange;
	}

    }
}