Enemy shouldn't see you through walls

Hi folks,

I am using Javascript and this is my script I have for now attached to my enemy.

 var Target : Transform;

 function Start ()
 {
     Target = GameObject.FindGameObjectWithTag("Player").transform;
 }
 
 function Update ()
 {
     var distance : float = Vector3.Distance(Target.position, transform.position);
     
     var targetDir = Target.position - transform.position;
     var forward = transform.forward;
     var angle = Vector3.Angle(targetDir, forward);
     
     if (angle < 45.0)
     {
         Debug.Log("Can see player");
     }
 }

Well the problem is, the enemy can see through walls what is not supposed to be. How can I make the enemy can't see you through walls?

Someone who can help me please? I am struggling now for days..

Thanks in advance