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

namespace BaseGames.World.Map
{
    /// <summary>
    /// 将玩家世界坐标转换为地图格子坐标，供 MapPanel / MinimapHUD 显示玩家位置图标。
    /// 挂在 Player GameObject 上（LateUpdate 每帧计算）。
    /// <para>
    /// 性能：首次启动时建立 Dictionary&lt;Vector2Int, string&gt; 空间索引，
    /// LateUpdate 房间判定为 O(1) 哈希查找。归一化位置每帧从世界坐标精确插值，
    /// 确保图标跟随玩家平滑移动，而非以格子步长离散跳动。
    /// </para>
    /// 通过 <see cref="ServiceLocator"/> 注册为 <see cref="IPlayerPositionProvider"/>。
    /// </summary>
    public class MapPlayerTracker : MonoBehaviour, IPlayerPositionProvider
    {
        [SerializeField] private Transform     _playerTransform;
        [SerializeField] private MapDatabaseSO _databaseOverride;  // 可选：直接指定；留空则从 IMapService 获取

        [Header("世界坐标 → 格子坐标换算参数")]
        [Tooltip("1 格对应的世界单位数。请在关卡编辑器中测量房间实际尺寸后填入，确保与关卡设计对齐。")]
        [SerializeField] private float _worldUnitsPerCell = 18f;

        /// <summary>玩家当前所在房间 ID；未在任何已知房间内时为 null。</summary>
        public string  CurrentRoomId              { get; private set; }

        /// <summary>
        /// 玩家在当前房间内的归一化坐标（0~1）。
        /// 基于世界坐标精确插值，每帧更新，可用于平滑移动图标。
        /// </summary>
        public Vector2 NormalizedPositionInRoom   { get; private set; }

        /// <summary>玩家进入新房间时触发（参数为新房间 ID）。</summary>
        public event Action<string> OnRoomChanged;

        private MapDatabaseSO                  _database;
        private Dictionary<Vector2Int, string> _cellToRoomId;
        private MapRoomDataSO                  _currentRoom;   // 当前房间数据缓存，避免 LateUpdate 每帧 GetRoom 查找
        private Vector2Int                     _lastCellPos = new Vector2Int(int.MinValue, int.MinValue);

        private void Awake()
        {
            // 单例保护：同一时刻只允许一个 IPlayerPositionProvider 存在
            if (ServiceLocator.GetOrDefault<IPlayerPositionProvider>() != null) return;
            ServiceLocator.Register<IPlayerPositionProvider>(this);
        }

        private void Start()
        {
            _database = _databaseOverride
                        ?? ServiceLocator.GetOrDefault<IMapService>()?.Database;
            BuildSpatialIndex();
        }

        private void OnDestroy()
        {
            ServiceLocator.Unregister<IPlayerPositionProvider>(this);
        }

        /// <summary>
        /// 构建格子坐标 → 房间 ID 的哈希映射，将 LateUpdate 的查询从 O(N) 降至 O(1)。
        /// 房间数据变化时（运行时热更）可再次调用重建索引。
        /// </summary>
        public void BuildSpatialIndex()
        {
            _cellToRoomId = new Dictionary<Vector2Int, string>();
            if (_database?.AllRooms == null) return;
            foreach (var room in _database.AllRooms)
            {
                if (room == null) continue;
                for (int x = 0; x < room.GridSize.x; x++)
                for (int y = 0; y < room.GridSize.y; y++)
                {
                    var cell = new Vector2Int(room.GridPosition.x + x, room.GridPosition.y + y);
                    _cellToRoomId[cell] = room.RoomId;
                }
            }
        }

        private void LateUpdate()
        {
            if (_playerTransform == null || _cellToRoomId == null) return;

            Vector2Int cellPos    = WorldToCell(_playerTransform.position);
            bool       cellChanged = cellPos != _lastCellPos;

            if (cellChanged)
            {
                _lastCellPos = cellPos;

                if (!_cellToRoomId.TryGetValue(cellPos, out var newRoomId))
                {
                    // 玩家离开所有已知房间
                    CurrentRoomId            = null;
                    _currentRoom             = null;
                    NormalizedPositionInRoom = Vector2.zero;
                    return;
                }

                var prevRoomId = CurrentRoomId;
                CurrentRoomId  = newRoomId;
                _currentRoom   = _database.GetRoom(newRoomId);

                if (newRoomId != prevRoomId)
                    OnRoomChanged?.Invoke(newRoomId);
            }

            // 每帧从世界坐标精确计算归一化位置，实现平滑图标跟随
            if (_currentRoom != null)
            {
                var worldMin  = new Vector2(
                    _currentRoom.GridPosition.x * _worldUnitsPerCell,
                    _currentRoom.GridPosition.y * _worldUnitsPerCell);
                var worldSize = new Vector2(
                    _currentRoom.GridSize.x * _worldUnitsPerCell,
                    _currentRoom.GridSize.y * _worldUnitsPerCell);
                var localPos = (Vector2)_playerTransform.position - worldMin;
                NormalizedPositionInRoom = new Vector2(
                    Mathf.Clamp01(localPos.x / Mathf.Max(1f, worldSize.x)),
                    Mathf.Clamp01(localPos.y / Mathf.Max(1f, worldSize.y)));
            }
        }

        private Vector2Int WorldToCell(Vector2 worldPos)
            => new(
                Mathf.FloorToInt(worldPos.x / _worldUnitsPerCell),
                Mathf.FloorToInt(worldPos.y / _worldUnitsPerCell));
    }
}