TowerShooter.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.InputSystem;
using System.Collections.Generic;

public class TowerShooter : MonoBehaviour
{
    public GameObject FirePoint;
    public GameObject Projectile;
    public GameObject Barrel;

    [SerializeField] private float range = 15f;
    [SerializeField] private string enemyTag = "Enemy";
    [SerializeField] private float ShootRate = 0.5f;
    [SerializeField] private float RotateSpeed = 10f;

    private float nextShoot = 0f;
    private GameObject Target;

    void Start()
    {
      // Every 0.5 seconds, search for a new target.
      InvokeRepeating("UpdateTarget", 0f, 0.5f);
    }

    // Obtain a new target
    void UpdateTarget() {
      // Get a list of all enemies in play.
      GameObject[] enemies = GameObject.FindGameObjectsWithTag(enemyTag);
      
      // We'll save which one is the closest by comparing against this variable. Default to infinity (so anything matches at first).
      float closestDistance = Mathf.Infinity;

      // A temp variable holding the closest enemy we find.
      GameObject newEnemy = null;

      // Loop through all enemies.
      foreach (GameObject enemy in enemies) {
        // Calculate their distance to the tower. 
        float distanceToEnemy = Vector3.Distance(transform.position, enemy.transform.position);
        
        // Only if they're within the tower's shooting range, will we consider them. 
        if(distanceToEnemy <= range) {
          // If this enemy is closer than our clostest variable, remember it. 
          if(distanceToEnemy < closestDistance) {
            newEnemy = enemy;
            closestDistance = distanceToEnemy;
          }
        }
      }

      // If we didn't find a new enemy, set our current Target to null and abort.
      if(newEnemy == null) {
        Target = null;
        return;
      }

      // If our new target is different from our existing target, look for its "Target" game object
      // so we know where to aim. If we can't find that game object, aim at its transform position (usually the feet). 
      if(newEnemy != Target) {
        GameObject targetX = GetChildWithName(newEnemy, "Target");
        if(targetX != null) {
          Target = targetX;
        } else {
          Target = newEnemy;
        }
      }
    }

    public void Fire() {
      // Instantiate a projectile from the firepoints position and orientation. 
      // FirePoint is a gameobject on the tower position where it shoots from. 
      Instantiate(Projectile, FirePoint.transform.position, FirePoint.transform.rotation);
    }

    private void Update() {
      // If we have a barrel object and have a target, Lerp towards the target (slowly rotate towards it). 
      if(Barrel != null && Target != null) {
        Quaternion newRot = Quaternion.LookRotation(Barrel.transform.position - Target.transform.position);
        Barrel.transform.rotation = Quaternion.Lerp(Barrel.transform.rotation, newRot, Time.deltaTime * RotateSpeed);
      }

      // If we have a target, start the shooting process. 
      if(Target != null) {
        // If next shoot is less than current game time, fire!
        if(nextShoot < Time.time) {
          // Do math that tells us if we are pointing at them. -0.993 or less means we are.
          Vector3 dir = (Target.transform.position - Barrel.transform.position).normalized;
          float dotProd = Vector3.Dot(dir, Barrel.transform.forward);

          // Only shoot if we're pointing at them.
          if(dotProd < -0.993) {
            // Set the next time we can shoot as "now + shoot rate"
            nextShoot = Time.time + ShootRate;
            Fire();
          }
        }
      }
    }

    // While in the editor, this will draw the tower's range so we can easily design the game.
    private void OnDrawGizmosSelected() {
      Gizmos.color = Color.red;
      Gizmos.DrawWireSphere(transform.position, range);
    }

    // Used to go through a gameobject's children and find one with a specific name.
    private GameObject GetChildWithName(GameObject obj, string name) {
        Transform trans = obj.transform;
        Transform childTrans = trans. Find(name);
        if (childTrans != null) {
            return childTrans.gameObject;
        } else {
            return null;
        }
    }
}