问为什么我的炮塔停止射击AI播放器？

EN

using UnityEngine;
using System.Collections;

public class TurretScript : MonoBehaviour {
public float rangeToPlayer;
public GameObject bullet;
public GameObject spawn;
private GameObject player;
private bool firing = false;
private float fireTime;
private float coolDown = 0.5F;

void Start () {
    player = GameObject.FindWithTag("Player");
}

void Update () {
    if ( PlayerInRange() ) {
        transform.LookAt(player.transform.position);
        RaycastHit hit;
        if( Physics.Raycast(transform.position, transform.TransformDirection(Vector3.forward), out hit )) {
            Debug.DrawRay(transform.position, transform.TransformDirection(Vector3.forward) * 20.0F, Color.red);
            if (hit.transform.gameObject.tag == "Player") {
                if ( firing == false )
                {       
                    firing = true;
                    fireTime = Time.time;
                    GameObject.Instantiate(bullet, spawn.transform.position, transform.rotation);
                }
            }
        }
    }
    if ( firing && fireTime + coolDown <= Time.time )
        firing = true;
}

bool PlayerInRange() {
    return ( Vector3.Distance(player.transform.position, transform.position) <= rangeToPlayer );
}
}