2d enemy ai

I want to make a enemy ai that patrols until it spots the player or it hears it shooting. if it spots the player it fires at him ( like the enemy soldiers from metal slug) this is what i have so far:

 using UnityEngine;
 using System.Collections;
 
 public class EnemyPatroll : MonoBehaviour {
 
 
     public float moveSpeed;
     public bool moveRight = false;
     public Transform wallCheck;
     public float wallCeckRadius;
     public LayerMask whatIsWall;
     private bool hittingWall;
 
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void Update () {
 
         hittingWall = Physics2D.OverlapCircle(wallCheck.position, wallCeckRadius, whatIsWall);
 
         if(hittingWall)
             moveRight = !moveRight;
 
 
         if(moveRight ){
         transform.localScale = new Vector3 (-1f, 1f,1f);
         GetComponent<Rigidbody2D>().velocity = new Vector2(moveSpeed,GetComponent<Rigidbody2D>().velocity.y);
         }
 
         else{
         transform.localScale = new Vector3 (1f, 1f,1f);
         GetComponent<Rigidbody2D>().velocity = new Vector2(-moveSpeed,GetComponent<Rigidbody2D>().velocity.y);
         }
     }
 }