using System.Collections.Generic;
using UnityEngine;
using BaseGames.Core.Events;

namespace BaseGames.Enemies
{
    /// <summary>
    /// 敌人 BehaviorTree 配额管理器（架构 07_EnemyModule §13）。
    /// 每 REBALANCE_INTERVAL 帧，按到玩家距离排序已注册敌人，
    /// 仅对最近的 _maxActiveBehaviorTrees 个敌人启用 BT。
    /// 挂载在场景管理器 GameObject 上（每场景一个实例）。
    /// </summary>
    public class EnemyQuotaManager : MonoBehaviour
    {
        [SerializeField, Min(1)] private int _maxActiveBehaviorTrees = 12;
        [Tooltip("PlayerController.Start() 广播此频道，替代 FindWithTag")]
        [SerializeField] private TransformEventChannelSO _onPlayerSpawned;

        private const int REBALANCE_INTERVAL = 10;

        private int _frameCount;
        // _registeredSet 用于 O(1) 重复检测，_registered List 用于 Sort
        private readonly HashSet<EnemyBase>         _registeredSet = new();
        private readonly List<EnemyBase>             _registered    = new();
        private readonly Dictionary<EnemyBase, int>  _indexMap      = new();
        // 排序临时缓冲区：预计算每个敌人到玩家的距离，避免 Sort 比较器内重复 Vector3 运算（O(n logn) → O(n)）
        private readonly List<(EnemyBase enemy, float sqDist)> _sortTemp = new();
        // 缓存玩家 Transform
        private Transform _playerTransform;
        private readonly CompositeDisposable _subs = new();

        private void OnEnable()
        {
            _onPlayerSpawned?.Subscribe(OnPlayerSpawned).AddTo(_subs);
        }

        private void OnDisable() => _subs.Clear();

        private void OnPlayerSpawned(Transform playerTransform)
            => _playerTransform = playerTransform;

        // ── 注册 / 注销 ───────────────────────────────────────────────────
        public void Register(EnemyBase enemy)
        {
            if (enemy != null && _registeredSet.Add(enemy))
            {
                _indexMap[enemy] = _registered.Count;
                _registered.Add(enemy);
            }
        }

        public void Unregister(EnemyBase enemy)
        {
            if (enemy == null || !_registeredSet.Remove(enemy)) return;
            int idx  = _indexMap[enemy];
            int last = _registered.Count - 1;
            if (idx != last)
            {
                var moved        = _registered[last];
                _registered[idx] = moved;
                _indexMap[moved] = idx;
            }
            _registered.RemoveAt(last);
            _indexMap.Remove(enemy);
        }

        // ── Unity 生命周期 ────────────────────────────────────────────────
        private void Update()
        {
            if (++_frameCount % REBALANCE_INTERVAL == 0)
                Rebalance();
        }

        // ── 内部 ──────────────────────────────────────────────────────────
        private void Rebalance()
        {
            int n = _registered.Count;
            if (n == 0) return;

            var playerPos = _playerTransform != null ? _playerTransform.position : Vector3.zero;

            // ① 预计算距离（O(n) Vector3 运算，而非在比较器内重复执行 O(n logn) 次）
            _sortTemp.Clear();
            for (int i = 0; i < n; i++)
            {
                var e = _registered[i];
                float sqd = e != null
                    ? (e.transform.position - playerPos).sqrMagnitude
                    : float.MaxValue;
                _sortTemp.Add((e, sqd));
            }

            // ② 对临时列表排序（比较器只做 float 比较，无额外 Vector3 开销）
            _sortTemp.Sort(static (a, b) => a.sqDist.CompareTo(b.sqDist));

            // ③ 将排序结果写回 _registered，同步重建 _indexMap（修复排序后索引过期的 bug）
            for (int i = 0; i < n; i++)
            {
                var e = _sortTemp[i].enemy;
                _registered[i] = e;
                if (e != null) _indexMap[e] = i;
            }

#if GRAPH_DESIGNER
            for (int i = n - 1; i >= 0; i--)
            {
                var enemy = _registered[i];
                if (enemy == null) { _registered.RemoveAt(i); continue; }

                var bt     = enemy.BehaviorTree;
                bool active = i < _maxActiveBehaviorTrees;

                if (bt != null && bt.enabled != active)
                {
                    bt.enabled = active;
                    // 同步暂停/恢复感知系统，避免远处敌人无效 tick
                    enemy.SensorHub?.SetSuspended(!active);
                }
            }
#endif
        }
    }
}