Unity Navmesh agent patrol and chase player script issues.

I just began scripting for the first time and am completely stuck with trying to convert this script from a simple patrol script to a script where the enemy will leave the patrol and chase the player the second the player comes into his view. Once I figure this all out I can start working on making attack scripts and game state changes.

If anyone can tell me how they would do it or just send me a tutorial, I'd appreciate it. I have seen multiple patrol tutorials but combining the chase script I have with the ray and the patrol script seems to just keep failing. I have worked a few days on this problem but am running out of time and have to work on other parts of the assignment as well.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class NPCSimplePatrol : MonoBehaviour {
 
     //Dictates whether the agent waits on each node.
     [SerializeField]
     bool _patrolWaiting;
 
     //The total time we wait at each node.
     [SerializeField]
     float _totalWaitTime = 3f;
 
     //The probability of switching direction.
     [SerializeField]
     float _switchProbability = 0.2f;
 
     //The list of all patrol nodes to visit.
     [SerializeField]
     List<Waypoint> _patrolPoints;
 
     //Private variables for base behaviour.
     UnityEngine.AI.NavMeshAgent _navMeshAgent;
     int _currentPatrolIndex;
     bool _travelling;
     bool _waiting;
     bool _patrolForward;
     float _waitTimer;
 
     // Use this for initialization
     public void Start()
     {
         _navMeshAgent = this.GetComponent<UnityEngine.AI.NavMeshAgent>();
 
         if (_navMeshAgent == null)
         {
             Debug.LogError("The nav mesh agent component is not attached to " + gameObject.name);
         }
         else
         {
             if (_patrolPoints != null && _patrolPoints.Count >= 2)
             {
                 _currentPatrolIndex = 0;
                 SetDestination();
             }
             else
             {
                 Debug.Log("Insufficient patrol points for basic patrolling behaviour.");
             }
 
         }
     }
 
     
     public void Update()
     {
         Debug.Log(_patrolWaiting);
         //Check if we're close to the destination.
         if (_travelling && _navMeshAgent.remainingDistance <= 1.0f)
         {
             _travelling = false;
 
             //If we're going to wait, then wait.
             if (_patrolWaiting)
             {
                 _waiting = true;
                 _waitTimer = 0f;
             }
             else
             {
                 ChangePatrolPoint();
                 SetDestination();
             }
         }
       
         //Instead if we're waiting.
         if (_waiting)
         {
             _waitTimer += Time.deltaTime;
             if (_waitTimer >= _totalWaitTime)
             {
                 _waiting = false;
 
                 ChangePatrolPoint();
                 SetDestination();
             }
         }
     }
 
     private void SetDestination()
     {
         if (_patrolPoints != null)
         {
             Vector3 targetVector = _patrolPoints[_currentPatrolIndex].transform.position;
             _navMeshAgent.SetDestination(targetVector);
             _travelling = true;
         }
     }
 
     /// <summary>
     /// Selects a new patrol point in the available list, but
     /// also with a small probability allows for us to move forward or backwards.
     /// </summary>
     private void ChangePatrolPoint()
     {
         if (UnityEngine.Random.Range(0f, 1f) <= _switchProbability)
         {
             _patrolForward = !_patrolForward;
         }
 
         if (_patrolForward)
         {
             _currentPatrolIndex = (_currentPatrolIndex + 1) % _patrolPoints.Count;
         }
         else
         {
             if (--_currentPatrolIndex < 0)
             {
                 _currentPatrolIndex = _patrolPoints.Count - 1;
             }       
         }
     }
 }