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

namespace BaseGames.World
{
    /// <summary>
    /// 玩家面包屑轨迹追踪器（架构 21_LiquidPuzzleModule §15）。
    /// 每 RecordInterval 秒记录一次玩家位置（仅当移动距离超过 MinMoveDistance 时）。
    /// 最多保存 MaxCrumbs 个历史位置，超出后移除最旧的。
    /// </summary>
    public class BreadcrumbTracker : MonoBehaviour
    {
        [SerializeField, Min(0.1f)] private float _recordInterval  = 2f;
        [SerializeField, Min(1)]    private int   _maxCrumbs       = 20;
        [SerializeField, Min(0.1f)] private float _minMoveDistance = 1f;

        [Header("事件频道")]
        [SerializeField] private TransformEventChannelSO _onPlayerSpawned;

        private readonly Queue<Vector2>      _crumbs = new();
        private readonly CompositeDisposable _subs   = new();
        private Vector2                      _lastPos;
        private float                        _timer;

        private Transform _playerTransform;

        // ── Unity 生命周期 ────────────────────────────────────────────────
        private void OnEnable()
        {
            _onPlayerSpawned?.Subscribe(t => _playerTransform = t).AddTo(_subs);
        }

        private void OnDisable()
        {
            _subs.Clear();
        }

        private void Update()
        {
            if (_playerTransform == null) return;

            _timer += Time.deltaTime;
            if (_timer < _recordInterval) return;
            _timer = 0f;

            Vector2 pos = _playerTransform.position;
            if (_crumbs.Count > 0 && Vector2.Distance(pos, _lastPos) < _minMoveDistance)
                return;

            _crumbs.Enqueue(pos);
            _lastPos = pos;

            while (_crumbs.Count > _maxCrumbs)
                _crumbs.Dequeue();
        }

        // ── 公共 API ──────────────────────────────────────────────────────
        /// <summary>返回最近 count 个面包屑位置（从旧到新排列）。</summary>
        public IReadOnlyList<Vector2> GetRecentCrumbs(int count)
        {
            var result = new List<Vector2>(_crumbs);
            if (result.Count <= count) return result;
            return result.GetRange(result.Count - count, count);
        }

        /// <summary>清空全部轨迹记录（如死亡后重生时调用）。</summary>
        public void Clear() => _crumbs.Clear();
    }
}