NavMesh

using UnityEngine;
using UnityEngine.AI;

public class EnemyAI : MonoBehaviour
{
  public Transform player;
  public float chaseRange   = 15f;
  public float attackRange  = 2f;
  public float updateRate   = 0.2f; // Recompute path every 0.2s

  NavMeshAgent agent;
  Animator anim;
  float nextUpdate;

  void Awake()
  {
      agent = GetComponent<NavMeshAgent>();
      anim  = GetComponent<Animator>();
  }

  void Update()
  {
      float dist = Vector3.Distance(transform.position, player.position);

      if (dist < chaseRange && Time.time >= nextUpdate)
      {
          nextUpdate = Time.time + updateRate;
          agent.SetDestination(player.position);
      }

      // Drive Animator from agent speed
      anim.SetFloat("Speed", agent.velocity.magnitude);

      if (dist < attackRange)
      {
          agent.ResetPath(); // Stop moving
          anim.SetTrigger("Attack");
      }
  }
}

using UnityEngine;
using UnityEngine.AI;

public class PatrolAI : MonoBehaviour
{
  public Transform[] waypoints;
  public float detectRange = 8f;
  public Transform player;

  NavMeshAgent agent;
  int current = 0;
  enum State { Patrol, Chase, Investigate }
  State state = State.Patrol;

  void Awake() => agent = GetComponent<NavMeshAgent>();

  void Start() => GotoNextWaypoint();

  void Update()
  {
      float dist = Vector3.Distance(transform.position, player.position);

      switch (state)
      {
          case State.Patrol:
              if (dist < detectRange) { state = State.Chase; break; }
              if (!agent.pathPending && agent.remainingDistance < 0.5f)
                  GotoNextWaypoint();
              break;

          case State.Chase:
              agent.SetDestination(player.position);
              if (dist > detectRange * 1.5f)
                  state = State.Investigate;
              break;

          case State.Investigate:
              if (!agent.pathPending && agent.remainingDistance < 0.5f)
              { state = State.Patrol; GotoNextWaypoint(); }
              break;
      }
  }

  void GotoNextWaypoint()
  {
      if (waypoints.Length == 0) return;
      agent.SetDestination(waypoints[current].position);
      current = (current + 1) % waypoints.Length;
  }
}