Locking onto a enemy until its dead

Questions & Answers
1

I made a script which looks at an enemy and shoots at it as long as i hold the mouse button onto it, but i cant figure out how to make it lock onto the enemy only by clicking once and then let it go when the enemy dies.

Player code:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.AI;

public class PlayerController : MonoBehaviour
{
    public Camera cam;
    public NavMeshAgent agent;

    public float damage = 10f;
    public float range = 100f;
    public float rotspeed = 10f;
    public GameObject Gun;
    public Quaternion targetRotation;
    public float impactForce = 10f;
    public float firerate = 0f;
    private float nextTimeToFire = 0f;
    public ParticleSystem flash;
    public GameObject impact;
    void Start()
    {

    }

    // Update is called once per frame
    void Update()
    {
        if (Input.GetMouseButton(0) )//&& Time.time >= nextTimeToFire)
        {
            Ray ray = cam.ScreenPointToRay(Input.mousePosition);
            RaycastHit hit;

            if (Physics.Raycast(ray, out hit))
            {
                if (hit.transform.gameObject.layer == LayerMask.NameToLayer("Default"))
                {
                    agent.SetDestination(hit.point);
                }
                else if (hit.transform.gameObject.layer == LayerMask.NameToLayer("Enemy"))
                {
                        targetRotation = Quaternion.LookRotation(hit.point - transform.position);
                        transform.rotation = Quaternion.Slerp(transform.rotation, targetRotation, rotspeed * Time.deltaTime);

                        Shoot();
                }
            }
        }


    }
    void Shoot()
    {   
        if (Time.time >= nextTimeToFire)
        {   
            flash.Play();
            nextTimeToFire = Time.time + 1f / firerate;
            RaycastHit hit;
            if (Physics.Raycast(Gun.transform.position, Gun.transform.forward, out hit, range))
            {
                Debug.Log(hit.transform.name);
                Target target = hit.transform.GetComponent<Target>();

                if (target != null)
                {
                    target.TakeDamage(damage);
                }
                if (hit.rigidbody != null)
                {
                    hit.rigidbody.AddForce(-hit.normal * impactForce);
                }

                GameObject impactGO = Instantiate(impact, hit.point, Quaternion.LookRotation(hit.normal));
                Destroy(impactGO, 1f);
            }
        }
    }
}

Enemy code:

public class Target : MonoBehaviour
{   
    public float hp = 50f;
    public void TakeDamage (float amount)
    {
        hp -= amount;
        if (hp <= 0f)
        {
            Die();
        }
    }
    void Die()
    {
        Destroy(gameObject);
    }
2

You can add a trigger boolean and store values for the enemy:

  bool targeting = false;
  GameObject targetEnemy;
  Transform targetPoint;
  // Update is called once per frame
     void Update()
     {
         if (Input.GetMouseButton(0) )//&& Time.time >= nextTimeToFire)
         {
             Ray ray = cam.ScreenPointToRay(Input.mousePosition);
             RaycastHit hit;
 
             if (Physics.Raycast(ray, out hit))
             {
                 if (hit.transform.gameObject.layer == LayerMask.NameToLayer("Default"))
                 {
                     agent.SetDestination(hit.point);
                 }
                 else if (hit.transform.gameObject.layer == LayerMask.NameToLayer("Enemy"))
                 {
                         targeting = true;
                         targetEnemy = hit.transform.gameObject;
                         targetPoint = hit.point;

                         targetRotation = Quaternion.LookRotation(hit.point - transform.position);
                         transform.rotation = Quaternion.Slerp(transform.rotation, targetRotation, rotspeed * Time.deltaTime);
 
                         Shoot();
                 }
             }
         }
         else if(targeting)
         {
              if(targetEnemy.GetComponent<Target>().hp < 0f)
              {
                  targeting = false;
                  targetEnemy = null;
                  targetpoint = null;
              }
              else
              {
                  targetRotation = Quaternion.LookRotation(targetPoint - transform.position);
                  transform.rotation = Quaternion.Slerp(transform.rotation, targetRotation, rotspeed * Time.deltaTime);
 
                  Shoot();
              }
         }
 
     }

Hope this helps!