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

namespace BaseGames.World
{
    /// <summary>
    /// 移动平台。Kinematic Rigidbody2D，支持三种移动模式。
    ///
    /// 乘客跟随（Delta Position 方案，替代 SetParent）：
    ///   - PassengerSensor（Trigger）检测进入乘客（<see cref="IPassengerReceiver"/>）。
    ///   - FixedUpdate(-300) 计算本帧期望位移 delta，推送给所有乘客，再执行 MovePosition。
    ///   - 乘客在自己的 FixedUpdate(-200) 最前端消费 delta：_rb.position += delta。
    ///   - 乘客离台时通过 OnLeavePlatform 继承平台速度，避免卡顿。
    ///
    /// 此方案不修改 Transform 层级，与动画/摄像机/HitBox 系统完全兼容。
    /// </summary>
    [DefaultExecutionOrder(-300)]
    [RequireComponent(typeof(Rigidbody2D))]
    public class MovingPlatform : MonoBehaviour
    {
        public enum MoveType { LinearAB, WayPoints, TriggeredLinear }

        [Header("移动配置")]
        [SerializeField] private MoveType    _moveType        = MoveType.LinearAB;
        [SerializeField] private Transform[] _wayPoints;
        [SerializeField] private float       _speed           = 3f;
        [SerializeField] private float       _waitAtEndpoint  = 0.5f;

        [Header("TriggeredLinear 模式")]
        [SerializeField] private VoidEventChannelSO _activationChannel;

        [Header("乘客检测")]
        [SerializeField] private BoxCollider2D _passengerSensor;  // isTrigger，检测乘客
        [SerializeField] private LayerMask     _passengerLayer;   // 应包含 Player + Enemy 层

        private Rigidbody2D                  _rb;
        private readonly List<IPassengerReceiver> _passengers = new();
        private readonly List<IPassengerReceiver> _passengerSnapshot = new(); // 迭代快照，防并发修改
        private int                          _waypointIndex;
        private bool                         _movingForward = true;
        private bool                         _triggered;
        private bool                         _waiting;
        private Vector2                      _frameVelocity;    // 本帧实际速度，供离台时继承
        private WaitForSeconds               _waitForEndpoint;
        private readonly CompositeDisposable _subs = new();

        private void Awake()
        {
            _rb = GetComponent<Rigidbody2D>();
            _rb.bodyType      = RigidbodyType2D.Kinematic;
            _rb.interpolation = RigidbodyInterpolation2D.Interpolate;
            _waitForEndpoint  = new WaitForSeconds(_waitAtEndpoint);
        }

        private void OnEnable()
        {
            _activationChannel?.Subscribe(OnTriggered).AddTo(_subs);
        }

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

        private void FixedUpdate()
        {
            if (_wayPoints == null || _wayPoints.Length == 0)
            {
                _frameVelocity = Vector2.zero;
                return;
            }
            if (_moveType == MoveType.TriggeredLinear && !_triggered)
            {
                _frameVelocity = Vector2.zero;
                return;
            }
            if (_waiting)
            {
                _frameVelocity = Vector2.zero;
                return;
            }

            MoveAndBroadcast();
        }

        private void MoveAndBroadcast()
        {
            var target = (Vector2)_wayPoints[_waypointIndex].position;
            var next   = Vector2.MoveTowards(_rb.position, target, _speed * Time.fixedDeltaTime);

            // 计算期望 delta（在 MovePosition 执行前，不依赖物理步骤是否完成）
            Vector2 delta = next - _rb.position;
            _frameVelocity = delta / Time.fixedDeltaTime;

            // 先广播 delta，乘客在下一个 FixedUpdate(-200) 消费
            _passengerSnapshot.Clear();
            _passengerSnapshot.AddRange(_passengers);
            foreach (var r in _passengerSnapshot)
                r.SetPlatformDelta(delta);

            _rb.MovePosition(next);

            if (Vector2.Distance(_rb.position, target) < 0.02f)
                StartCoroutine(WaitAndAdvance());
        }

        private IEnumerator WaitAndAdvance()
        {
            _waiting = true;
            yield return _waitForEndpoint;
            AdvanceWaypoint();
            _waiting = false;
        }

        private void AdvanceWaypoint()
        {
            if (_moveType == MoveType.TriggeredLinear)
            {
                _waypointIndex = Mathf.Min(_waypointIndex + 1, _wayPoints.Length - 1);
                if (_waypointIndex == _wayPoints.Length - 1)
                    _triggered = false;
                return;
            }

            if (_moveType == MoveType.LinearAB)
            {
                _movingForward = !_movingForward;
                _waypointIndex = _movingForward ? 1 : 0;
            }
            else // WayPoints
            {
                _waypointIndex = (_waypointIndex + 1) % _wayPoints.Length;
            }
        }

        private void OnTriggered() => _triggered = true;

        // ── Passenger Detection ───────────────────────────────────────────────

        private void OnTriggerEnter2D(Collider2D other)
        {
            if (!IsPassengerLayer(other)) return;
            if (!other.TryGetComponent<IPassengerReceiver>(out var receiver)) return;
            if (!_passengers.Contains(receiver))
                _passengers.Add(receiver);
        }

        private void OnTriggerExit2D(Collider2D other)
        {
            if (!other.TryGetComponent<IPassengerReceiver>(out var receiver)) return;
            if (!_passengers.Remove(receiver)) return;

            // 继承平台速度，防止离台时速度骤变卡顿
            receiver.OnLeavePlatform(_frameVelocity);
        }

        private bool IsPassengerLayer(Collider2D col)
            => (_passengerLayer.value & (1 << col.gameObject.layer)) != 0;

#if UNITY_EDITOR
        private void OnDrawGizmos()
        {
            if (_wayPoints == null || _wayPoints.Length < 2) return;
            Gizmos.color = new Color(1f, 0.8f, 0f, 0.8f);
            for (int i = 0; i < _wayPoints.Length - 1; i++)
            {
                if (_wayPoints[i] != null && _wayPoints[i + 1] != null)
                    Gizmos.DrawLine(_wayPoints[i].position, _wayPoints[i + 1].position);
            }
        }
#endif
    }
}