using System;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;
using System.Collections;
using System.Collections.Generic;
using DG.Tweening;
using Sirenix.OdinInspector;

namespace Ichni.Menu.UI
{
// 一个完全自定义的列表控制器，实现了拖拽、惯性、边界和吸附
    public class SongListControllerUI : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
    {
        [Title("核心组件")] 
        [SerializeField] public RectTransform content;
        [SerializeField] public RectTransform viewport;

        [Title("预制体")] 
        [SerializeField] 
        private GameObject songItemPrefab;

        [Title("对齐与动画")] 
        [SerializeField] public RectTransform centerPoint;
        [SerializeField] private float snapSpeed = 5f;
        [SerializeField] private float decelerationRate = 0.135f;

        [Title("平滑度优化")] 
        [SerializeField] [Range(1f, 20f)]
        private float dragSmoothing = 16f; // 拖拽平滑度的阻尼值，可在Inspector中调节
        [SerializeField][Range(1f, 20f)]
        private float releaseSmoothing = 4f; // 松手后平滑度的阻尼值，可在Inspector中调节
        
        [Title("甩动判定")]
        [Tooltip("当松手时的速度大于此值，才会被判定为一次“甩动”并产生惯性")]
        [SerializeField] private float flickThreshold = 50f;

        public SongSelectionTab selectedTab;

        // 内部变量
        private List<RectTransform> songItems = new List<RectTransform>();
        private Vector2 velocity;
        private bool isDragging = false;
        public float topBound;
        public float bottomBound = 0f;
        private Vector2 targetPosition; // 【新增】内容的目标位置
        private float targetX = 1500f;
        public bool isDuringSnap = false;
        public RectTransform closestTab;

        void Start()
        {
            InitializeList();
            targetPosition = content.anchoredPosition; // 初始化目标位置
            targetX = -1500f;
        }

        private void Update()
        {
            RectTransform closestItem = closestTab;
            float cloesestY = Mathf.Infinity;
            foreach (RectTransform item in songItems)
            {
                float distance = Mathf.Abs(item.position.y - centerPoint.position.y);
                if (distance < cloesestY)
                {
                    cloesestY = distance;
                    closestItem = item;
                }
            }
            
            if (closestItem != null && closestTab != closestItem)
            {
                closestTab = closestItem;
                MenuAudioManager.instance.audioContainer.PlaySoundFX("SelectTab");
            }
        }

        // 使用LateUpdate来处理所有位置更新，防止抖动
        void LateUpdate()
        {
            // 如果不在拖拽，则处理惯性
            // 注意：我们只在 isDragging 为 false 时处理惯性，
            // OnEndDrag中已经对速度进行了判断，所以这里的逻辑依然适用
            if (!isDragging && Mathf.Abs(velocity.y) > 0.1f)
            {
                // 将速度施加于目标位置
                targetPosition.y += velocity.y * Time.deltaTime;
                // 速度衰减
                velocity *= (1 - decelerationRate);

                // 当速度足够小时，停止惯性并触发吸附
                if (Mathf.Abs(velocity.y) <= 0.1f)
                {
                    velocity = Vector2.zero;
                    StartCoroutine(SnapToClosest());
                }
            }
            
            // 无论何时，都将Content的实际位置平滑地Lerp到目标位置
            float damping = isDragging ? dragSmoothing : releaseSmoothing;
            Vector2 finalPosition = Vector2.Lerp(content.anchoredPosition, targetPosition, Time.deltaTime * damping);
            finalPosition.x = targetX;
            content.anchoredPosition = finalPosition;
            // 每次更新后都施加边界限制
            ClampContentPosition();
        }

        void InitializeList()
        {
            // ... (这部分代码无需改动)
            foreach (Transform child in content)
            {
                Destroy(child.gameObject);
            }
            songItems.Clear();
            
            if (songItemPrefab != null)
            {
                GenerateSongTabs();
            }

            Canvas.ForceUpdateCanvases();
            topBound = -songItems[^1].anchoredPosition.y;
            bottomBound = -songItems[0].anchoredPosition.y;
            if (songItems.Count > 0)
            {
                StartCoroutine(SnapToItem(songItems[0], true));
            }
            
            closestTab = songItems[0];
        }

        public void GenerateSongTabs()
        {
            ChapterSelectionUnit chapterUnit = ChapterSelectionManager.instance.currentChapter;
            foreach (SongItemData song in chapterUnit.songs)
            {
                SongSelectionTab tab = Instantiate(songItemPrefab ,content).GetComponent<SongSelectionTab>();
                songItems.Add(tab.GetComponent<RectTransform>());
                tab.SetUpTab(song);
            }
        }
        
        public void OnBeginDrag(PointerEventData eventData)
        {
            isDragging = true;
            velocity = Vector2.zero;
            StopAllCoroutines();
            // 开始拖拽时，将目标位置与当前位置同步
            targetPosition = content.anchoredPosition;
            
            selectedTab?.SetSelection(false);
            selectedTab = null; // 清除当前选中的Tab

            //DOTween.To(x=>targetX = x, targetX, -1550f, 0.2f).SetEase(Ease.OutQuad).Play();
            //songItems.ForEach(item => item.DOScale(1.1f,0.2f).SetEase(Ease.OutQuad).Play());
        }

        public void OnDrag(PointerEventData eventData)
        {
            // 拖拽时，只更新目标位置，而不是直接移动Content
            targetPosition += new Vector2(0, eventData.delta.y);

            // 【核心修正 #1】计算速度时，只使用Y轴分量
            velocity = new Vector2(0, eventData.delta.y / Time.deltaTime);
        }
        
        public void OnEndDrag(PointerEventData eventData)
        {
            isDragging = false;
            //DOTween.To(x => targetX = x, targetX, -1500f, 0.2f).SetEase(Ease.OutQuad).Play();
            //songItems.ForEach(item => item.DOScale(1,0.2f).SetEase(Ease.OutQuad).Play());

            // 【核心修正】在这里根据速度决定下一步做什么
            if (Mathf.Abs(velocity.y) > flickThreshold)
            {
                // 速度足够大，是“甩动”，让 LateUpdate 中的惯性逻辑接管
                // 我们什么都不用做，LateUpdate会自动处理
            }
            else
            {
                // 速度很小，是“慢速拖拽”，立即开始吸附
                velocity = Vector2.zero; // 清除残余速度
                StartCoroutine(SnapToClosest());
            }
        }

        private void ClampContentPosition()
        {
            // 【核心修正 #2】现在我们限制的是目标位置，让Lerp去处理实际位置
            targetPosition.y = Mathf.Clamp(targetPosition.y, bottomBound, topBound);
        }

        // SnapToClosest 和 SnapToItem 这两个协程也需要微调，以确保它们能正确地与新的平滑系统协作
        private IEnumerator SnapToClosest()
        {
            // ... (寻找最近项的逻辑不变) ...
            yield return new WaitForEndOfFrame();
            float minDistance = float.MaxValue;
            RectTransform closestItem = null;
            foreach (RectTransform item in songItems)
            {
                float distance = Mathf.Abs(item.position.y - centerPoint.position.y);
                if (distance < minDistance)
                {
                    minDistance = distance;
                    closestItem = item;
                }
            }

            if (closestItem != null)
            {
                yield return SnapToItem(closestItem, false);
            }
        }

        public IEnumerator SnapCoroutine;
        
        public IEnumerator SnapToTab(SongSelectionTab tab)
        {
            selectedTab?.SetSelection(false);
            selectedTab = null; // 清除当前选中的Tab

            if(isDuringSnap && SnapCoroutine != null) StopCoroutine(SnapCoroutine);
            
            SnapCoroutine = SnapToItem(tab.GetComponent<RectTransform>(), false);
            
            yield return StartCoroutine(SnapCoroutine);
        }

        private IEnumerator SnapToItem(RectTransform targetItem, bool immediate)
        {
            if (!immediate)
            {
                yield return new WaitForEndOfFrame();
            }
            
            Debug.Log("开始对齐到: " + targetItem.name);
            
            selectedTab = targetItem.GetComponent<SongSelectionTab>();
            selectedTab.SetSelection(true);
            
            SongItemData connectedSong = selectedTab.connectedSong;
            MenuManager.instance.songSelectionUIPage.selectedSong = connectedSong;
            MenuManager.instance.songSelectionUIPage.selectedSave = GameSaveManager.instance.SongSaveModule.GetSongStatusSave(connectedSong.songName);
          
            Vector3 closestItemLocalPos = viewport.InverseTransformPoint(targetItem.position);
            Vector3 centerPointLocalPos = viewport.InverseTransformPoint(centerPoint.position);
            float localOffsetY = centerPointLocalPos.y - closestItemLocalPos.y;

            // 【核心修正 #3】吸附动画现在也是通过更新targetPosition来实现
            Vector2 finalTargetPosition = content.anchoredPosition + new Vector2(0, localOffsetY);
            finalTargetPosition.y = Mathf.Clamp(finalTargetPosition.y, bottomBound, topBound);

            if (immediate)
            {
                // 立即模式：直接设置Content和Target
                targetPosition = finalTargetPosition;
                content.anchoredPosition = finalTargetPosition;
            }
            else
            {
                isDuringSnap = true;
                // 动画模式：只更新Target，让LateUpdate中的Lerp来完成动画
                targetPosition = finalTargetPosition;

                // 我们也可以在这里保留一个独立的Lerp循环，以使用不同的snapSpeed
                velocity = Vector2.zero;
                while (Mathf.Abs(content.anchoredPosition.y - targetPosition.y) > 1f)
                {
                    content.anchoredPosition = Vector2.Lerp(content.anchoredPosition, targetPosition, Time.deltaTime * snapSpeed);
                    yield return null;
                }

                content.anchoredPosition = targetPosition;
            }

            Debug.Log($"已对齐到: {targetItem.GetComponent<SongSelectionTab>().songNameText.text}");
            
            
            SongSelectionManager.instance.SetPreview(connectedSong, selectedTab.isLocked);
            MenuManager.instance.songSelectionUIPage.difficultySelectionContainer.SetUp(connectedSong.difficultyDataList);
            MenuManager.instance.songSelectionUIPage.songInfoUI.SetIllustration(connectedSong.illustration, connectedSong.illustratorName);
            isDuringSnap = false;
        }
    }
}