examples/open_world_city/Assets/Scripts/NPCController.cs

using UnityEngine;
using UnityEngine.AI;

namespace UnityAgent
{
    /// <summary>
    /// AI NPC that wanders between random points and chases the player when
    /// they enter the aggro radius. Uses Unity's NavMeshAgent.
    /// </summary>
    [RequireComponent(typeof(NavMeshAgent))]
    public class NPCController : MonoBehaviour
    {
        public enum State { Idle, Wander, Chase }

        [Header("References")]
        public Transform player;

        [Header("Behaviour")]
        public State initialState = State.Wander;
        public float wanderRadius = 20f;
        public float aggroRange = 12f;
        public float loseSightRange = 20f;
        public float idleDuration = 2f;
        public float wanderSpeed = 2.5f;
        public float chaseSpeed = 5f;

        [Header("Debug")]
        public bool drawGizmos = true;

        private NavMeshAgent _agent;
        private State _state;
        private float _stateTimer;
        private Vector3 _startPos;

        private void Awake()
        {
            _agent = GetComponent<NavMeshAgent>();
            _agent.speed = wanderSpeed;
        }

        private void Start()
        {
            _state = initialState;
            _startPos = transform.position;
            if (player == null && GameObject.FindGameObjectWithTag("Player") != null)
                player = GameObject.FindGameObjectWithTag("Player").transform;
        }

        private void Update()
        {
            switch (_state)
            {
                case State.Idle: TickIdle(); break;
                case State.Wander: TickWander(); break;
                case State.Chase: TickChase(); break;
            }
        }

        private void TickIdle()
        {
            _stateTimer -= Time.deltaTime;
            if (PlayerInRange(aggroRange)) { EnterChase(); return; }
            if (_stateTimer <= 0f) EnterWander();
        }

        private void TickWander()
        {
            if (PlayerInRange(aggroRange)) { EnterChase(); return; }
            if (_agent.remainingDistance <= _agent.stoppingDistance && !_agent.pathPending)
                EnterIdle();
        }

        private void TickChase()
        {
            if (player == null) { EnterWander(); return; }
            _agent.SetDestination(player.position);

            if (!PlayerInRange(loseSightRange)) EnterWander();
        }

        private void EnterIdle()
        {
            _state = State.Idle;
            _stateTimer = idleDuration;
            _agent.isStopped = true;
        }

        private void EnterWander()
        {
            _state = State.Wander;
            _agent.speed = wanderSpeed;
            _agent.isStopped = false;
            Vector3 dir = Random.insideUnitSphere * wanderRadius;
            dir.y = 0f;
            Vector3 target = _startPos + dir;
            if (NavMesh.SamplePosition(target, out NavMeshHit hit, wanderRadius, NavMesh.AllAreas))
                _agent.SetDestination(hit.position);
        }

        private void EnterChase()
        {
            _state = State.Chase;
            _agent.speed = chaseSpeed;
            _agent.isStopped = false;
        }

        private bool PlayerInRange(float range)
        {
            if (player == null) return false;
            return Vector3.Distance(transform.position, player.position) <= range;
        }

        private void OnDrawGizmosSelected()
        {
            if (!drawGizmos) return;
            Gizmos.color = Color.yellow;
            Gizmos.DrawWireSphere(transform.position, aggroRange);
            Gizmos.color = Color.red;
            Gizmos.DrawWireSphere(transform.position, loseSightRange);
            Gizmos.color = Color.green;
            Gizmos.DrawWireSphere(_startPos == Vector3.zero ? transform.position : _startPos, wanderRadius);
        }
    }
}