How to create a view angle where the turret can see the enemy and start shooting

This is the script of my turret, how can I create a certain angle of view where the turret starts following the enemy? like this:

 public class Turret : MonoBehaviour
     {
         [Header("ATTRIBUTI")]
         public float speed = 10f;
         public float range = 10f;
         public float fireRate = 1f;
         private float fireCountdown = 0f;
         public float damage;
     
         public Bullet mybullet;
     
         [Header("Unity")]
         public GameObject bulletPrefab;
         public Transform target;
         public Transform firePoint;
         
         public string enemyTag = "Enemy";
     
         Vector3 lastKnowPosition = Vector3.zero;
         Quaternion lookAtRotation;
     
         void Start()
         {
             InvokeRepeating("UpdateTarget", 0f, 0.5f);
             mybullet.Damage = damage;
         }
     
         void Update()
         {
             if (target == null)
                 return;
             FollowTarget();
             if(fireCountdown <= 0f)
             {
                 Shoot();
                 fireCountdown = 1f / fireRate;
             }
             fireCountdown -= Time.deltaTime;
     
         }
     
         #region Shoot
         void Shoot()
         {
             GameObject bulletGO = (GameObject) Instantiate(bulletPrefab, firePoint.position, Quaternion.identity);
             Bullet bullet = bulletGO.GetComponent<Bullet>();
             if(bullet != null)
             {
                 bullet.Seek(target);
             }
         }
         #endregion
     
         #region Tracking Update
         void UpdateTarget()
         {
             GameObject[] enemies = GameObject.FindGameObjectsWithTag(enemyTag);
             float shortestDistance = Mathf.Infinity;
             GameObject nearestEnemy = null;
     
             foreach (GameObject enemy in enemies)
             {
                 float distanceToEnemy = Vector3.Distance(transform.position, enemy.transform.position);
                 if (distanceToEnemy < shortestDistance)
                 {
                     shortestDistance = distanceToEnemy;
                     nearestEnemy = enemy;
                 }
             }
             if (nearestEnemy != null && shortestDistance <= range)
             {
                 target = nearestEnemy.transform;
             }else
             {
                 target = null;
             }
         }
         #endregion
     
         #region Follow Target
         void FollowTarget()
         {
             if (target)
             {
                 if (lastKnowPosition != target.transform.position)
                 {
                     lastKnowPosition = target.transform.position;
                     lookAtRotation = Quaternion.LookRotation(lastKnowPosition - transform.position);
                 }
                 if (transform.rotation != lookAtRotation)
                 {
                     transform.rotation = Quaternion.RotateTowards(transform.rotation, lookAtRotation, speed * Time.deltaTime);
                 }
             }
     
         }
             #endregion
     
         #region Gizmos
             void OnDrawGizmos()
             {
                 Gizmos.color = Color.blue;
                 Gizmos.DrawSphere(transform.position, range);
             }
        
             #endregion  
     }