using System.Collections;
using System.Collections.Generic;
using Unity.Burst;
using Unity.Collections;
using Unity.Jobs;
using Unity.Mathematics;
using UnityEngine;
using UnityEngine.Jobs;

public class EnemyManagerBURST : MonoBehaviour
{
    [SerializeField] Transform _player;

    [SerializeField] List<EnemyUnitBURST> _enemies = new List<EnemyUnitBURST>(); // always up to date list of enemies

    NativeList<EnemyData> _enemyDatas; // any movement relevant data
    TransformAccessArray _transformAccessArray; // transforms for job system
    JobHandle? _moveJobHandle; // nullable for first run

    Transform[] _transformCache = new Transform[0]; // helper to set TransformAccessArray

    public void RegisterEnemy(EnemyUnitBURST enemy)
    {
        _enemies.Add(enemy);
    }
    public void UnRegisterEnemy(EnemyUnitBURST enemy)
    {
        _enemies.Remove(enemy);
    }

    private void Awake()
    {
        _enemyDatas = new NativeList<EnemyData>(0, Allocator.Persistent);
        _transformAccessArray = new TransformAccessArray(0);
    }
    private void OnDestroy()
    {
        _enemyDatas.Dispose();
        _transformAccessArray.Dispose();
    }

    private void Update()
    {
        HandleJobActions();
    }

    // is in own method so there is no return in Update, which can get confusing
    void HandleJobActions()
    {
        // job is running
        if (_moveJobHandle.HasValue && !_moveJobHandle.Value.IsCompleted) return;

        // complete the handle if it exists
        if (_moveJobHandle.HasValue)
        {
            _moveJobHandle.Value.Complete();
            Debug.Log($"Completed Job ...");
        }

        // update collections when the job is completed, so they are free
        UpdateNativeCollections();

        // start the job whenever the old one is completed
        RestartJob();
    }

    void UpdateNativeCollections()
    {
        if(_enemyDatas.Length != _enemies.Count || _transformAccessArray.length != _enemies.Count)
        {
            Debug.Log("Update Collections");
            _enemyDatas.Resize(_enemies.Count, NativeArrayOptions.UninitializedMemory);
            System.Array.Resize(ref _transformCache, _enemies.Count);

            for (int i = 0; i < _enemies.Count; i++)
            {
                _enemyDatas[i] = new EnemyData(_enemies[i]);
                _transformCache[i] = _enemies[i].transform;
            }
            // use helper array to set the TransformAccessArray
            _transformAccessArray.SetTransforms(_transformCache);
        }
    }

    void RestartJob()
    {
        var moveJob = new MoveJob
        {
            enemyDatas = _enemyDatas,
            deltaTime = Time.deltaTime,
            playerPosition = _player.position
        };
        _moveJobHandle = moveJob.Schedule(_transformAccessArray);
    }

    [BurstCompile]
    private struct MoveJob : IJobParallelForTransform
    {
        [ReadOnly] public float deltaTime;
        [ReadOnly] public float3 playerPosition;
        [ReadOnly] public NativeList<EnemyData> enemyDatas;

        public void Execute(int index, TransformAccess transform)
        {
            float3 direction = math.normalize(playerPosition - (float3)transform.position);
            transform.position = (float3)transform.position + (direction * enemyDatas[index].moveSpeed * deltaTime);
            transform.rotation = quaternion.LookRotation(direction, math.up());
        }
    }

    private struct EnemyData
    {
        public float moveSpeed;

        public EnemyData(EnemyUnitBURST enemyUnit)
        {
            this.moveSpeed = enemyUnit.moveSpeed;
        }
    }
}