using UnityEngine;
using UnityEngine.UI;
using TMPro;
using UnityEngine.SceneManagement;
using System.Collections;
using System.Collections.Generic;
using DG.Tweening;

public class SongSelectUI : MonoBehaviour
{
    public SongList songList;              // 存储歌曲列表的 ScriptableObject
    public GameObject songButtonPrefab;    // 歌曲按钮的 Prefab (Button)
    public Transform contentPanel;         // 滚动视图的 Content 面板

    [SerializeField] Button button_Main;
    [SerializeField] string ui_Main_Scene_Name = "UI_UI";
    [Header("Enter Animation")]
    [SerializeField] bool play_Enter_Anim = true;
    [SerializeField] float enter_Anim_Delay = 0.05f;
    [Header("Async Build")]
    [SerializeField] bool useAsyncBuild = true;
    [SerializeField] int buildBatch = 8;
    [Header("Switch Animations")]
    [SerializeField] bool play_Switch_Anim = true;
    [SerializeField] RectTransform list_Anim_Root;
    [SerializeField] float list_FadeOut_Time = 0.12f;
    [SerializeField] float list_FadeIn_Time = 0.18f;
    [SerializeField] float list_Move_Offset = 24f;
    [SerializeField] Ease list_Move_Ease = Ease.OutCubic;
    [SerializeField] bool list_Use_Unscaled = true;

    // Current DLC key used for per-DLC saved song selection
    public static string CurrentDlcKey = "dlc_default_0";

    // Track pending restore to avoid multiple overlapping restores
    private Coroutine restoreCoroutine;
    private Coroutine buildCoroutine;
    private Coroutine switchCoroutine;
    private CanvasGroup listCanvasGroup;
    private Vector2 listBasePos;
    private bool listBaseCached;

    void Start()
    {
        if (songList == null || songButtonPrefab == null || contentPanel == null)
        {
            Debug.LogError("请在 Inspector 中分配所有字段！");
            return;
        }

        button_Main.onClick.AddListener(
        () => StartCoroutine(LoadSceneAsync(ui_Main_Scene_NAME())));
        // Do not populate the song list at start. DLC buttons will request songs when clicked.

        if (play_Enter_Anim)
        {
            UI_SelectSong_EnterAnim anim = GetComponent<UI_SelectSong_EnterAnim>();
            if (anim == null)
            {
                anim = gameObject.AddComponent<UI_SelectSong_EnterAnim>();
            }
            anim.SetDelay(enter_Anim_Delay);
            anim.Play();
        }
    }

    private IEnumerator LoadSceneAsync(string sceneName)
    {
        AsyncOperation asyncLoad = SceneManager.LoadSceneAsync(sceneName, LoadSceneMode.Single);
        while (!asyncLoad.isDone)
        {
            yield return null;
        }
    }

    // 显示所有歌曲 (kept for manual use)
    public void DisplaySongs()
    {
        DisplaySongsFromList(songList != null ? songList.songs : null);
    }

    // Instantiate from a provided list (used by dlcButton to show DLC songs)
    public void DisplaySongsFromList(List<SongData> list)
    {
        if (buildCoroutine != null)
        {
            StopCoroutine(buildCoroutine);
        }
        if (switchCoroutine != null)
        {
            StopCoroutine(switchCoroutine);
            switchCoroutine = null;
        }
        if (play_Switch_Anim)
        {
            switchCoroutine = StartCoroutine(SwitchSongsRoutine(list));
        }
        else
        {
            buildCoroutine = StartCoroutine(BuildSongsAsync(list));
        }
    }

    private IEnumerator SwitchSongsRoutine(List<SongData> list)
    {
        yield return PlayListSwitchOut();
        yield return BuildSongsAsync(list);
        yield return PlayListSwitchIn();
        switchCoroutine = null;
    }

    private IEnumerator BuildSongsAsync(List<SongData> list)
    {
        ClearSongList();
        if (list == null)
        {
            buildCoroutine = null;
            yield break;
        }

        // allow UI to render a frame before heavy instantiation
        yield return null;

        int count = 0;
        foreach (var song in list)
        {
            InstantiateSongButton(song);
            count++;
            if (useAsyncBuild && buildBatch > 0 && (count % buildBatch) == 0)
            {
                yield return null;
            }
        }

        // After populating, attempt to restore per-DLC selected song (next frame to avoid stale objects)
        if (restoreCoroutine != null) StopCoroutine(restoreCoroutine);
        restoreCoroutine = StartCoroutine(RestoreSelectedSongNextFrame());
        buildCoroutine = null;
    }

    private RectTransform GetListAnimRoot()
    {
        if (list_Anim_Root != null)
        {
            return list_Anim_Root;
        }
        return contentPanel as RectTransform;
    }

    private CanvasGroup EnsureListCanvasGroup(RectTransform root)
    {
        if (root == null) return null;
        if (listCanvasGroup == null || listCanvasGroup.gameObject != root.gameObject)
        {
            listCanvasGroup = root.GetComponent<CanvasGroup>();
            if (listCanvasGroup == null)
            {
                listCanvasGroup = root.gameObject.AddComponent<CanvasGroup>();
            }
        }
        return listCanvasGroup;
    }

    private void CacheListBase(RectTransform root)
    {
        if (root == null) return;
        if (!listBaseCached)
        {
            listBasePos = root.anchoredPosition;
            listBaseCached = true;
        }
    }

    private IEnumerator PlayListSwitchOut()
    {
        if (!play_Switch_Anim)
        {
            yield break;
        }
        RectTransform root = GetListAnimRoot();
        if (root == null)
        {
            yield break;
        }
        CacheListBase(root);
        CanvasGroup cg = EnsureListCanvasGroup(root);
        if (cg == null)
        {
            yield break;
        }
        root.DOKill();
        cg.DOKill();
        float moveOffset = list_Move_Offset;
        if (root.GetComponent<LayoutGroup>() != null)
        {
            moveOffset = 0f;
        }
        Sequence seq = DOTween.Sequence().SetUpdate(list_Use_Unscaled);
        seq.Join(cg.DOFade(0f, list_FadeOut_Time));
        if (Mathf.Abs(moveOffset) > 0.01f)
        {
            seq.Join(root.DOAnchorPos(listBasePos + new Vector2(-moveOffset, 0f), list_FadeOut_Time).SetEase(list_Move_Ease));
        }
        yield return seq.WaitForCompletion();
    }

    private IEnumerator PlayListSwitchIn()
    {
        if (!play_Switch_Anim)
        {
            yield break;
        }
        RectTransform root = GetListAnimRoot();
        if (root == null)
        {
            yield break;
        }
        CacheListBase(root);
        CanvasGroup cg = EnsureListCanvasGroup(root);
        if (cg == null)
        {
            yield break;
        }
        root.DOKill();
        cg.DOKill();
        float moveOffset = list_Move_Offset;
        if (root.GetComponent<LayoutGroup>() != null)
        {
            moveOffset = 0f;
        }
        if (Mathf.Abs(moveOffset) > 0.01f)
        {
            root.anchoredPosition = listBasePos + new Vector2(moveOffset, 0f);
        }
        else
        {
            root.anchoredPosition = listBasePos;
        }
        cg.alpha = 0f;
        Sequence seq = DOTween.Sequence().SetUpdate(list_Use_Unscaled);
        seq.Join(cg.DOFade(1f, list_FadeIn_Time));
        if (Mathf.Abs(moveOffset) > 0.01f)
        {
            seq.Join(root.DOAnchorPos(listBasePos, list_FadeIn_Time).SetEase(list_Move_Ease));
        }
        yield return seq.WaitForCompletion();
    }

    private IEnumerator RestoreSelectedSongNextFrame()
    {
        // Wait one frame so Destroy() in ClearSongList fully completes and stale SongButtons are gone.
        yield return null;
        RestoreSelectedSongForCurrentDlc();
        restoreCoroutine = null;
    }

    private void RestoreSelectedSongForCurrentDlc()
    {
        // read saved index using CurrentDlcKey
        string dlcKey = (string.IsNullOrEmpty(CurrentDlcKey) ? "default_0" : CurrentDlcKey);
        string key = "song_selected_" + dlcKey;

        // collect song buttons under contentPanel
        var allSongButtons = contentPanel.GetComponentsInChildren<SongButton>(true);
        if (allSongButtons == null || allSongButtons.Length == 0)
        {
            Debug.LogWarning("SongSelectUI.RestoreSelectedSongForCurrentDlc: no song buttons found to restore selection");
            return;
        }

        // Ensure every DLC has a default persisted value (0)
        int savedIndex;
        if (!PlayerPrefs.HasKey(key))
        {
            PlayerPrefs.SetInt(key, 0);
            PlayerPrefs.Save();
            savedIndex = 0;
        }
        else
        {
            savedIndex = PlayerPrefs.GetInt(key, 0);
        }

        if (savedIndex < 0) savedIndex = 0;
        if (savedIndex >= allSongButtons.Length) savedIndex = 0;

        var btn = allSongButtons[savedIndex];
        if (btn == null)
        {
            // hard fallback to first
            btn = allSongButtons[0];
        }

        if (btn != null)
        {
            // simulate click
            btn.OnSongButtonClick();
            Debug.Log($"SongSelectUI: restored and clicked song index={savedIndex} for key={key}, totalButtons={allSongButtons.Length}");
        }
    }

    private void ClearSongList()
    {
        if (contentPanel == null) return;
        for (int i = contentPanel.childCount - 1; i >= 0; i--)
        {
#if UNITY_EDITOR
            if (!Application.isPlaying) DestroyImmediate(contentPanel.GetChild(i).gameObject);
            else Destroy(contentPanel.GetChild(i).gameObject);
#else
            Destroy(contentPanel.GetChild(i).gameObject);
#endif
        }
    }

    private void InstantiateSongButton(SongData song)
    {
        if (songButtonPrefab == null || contentPanel == null) return;

        GameObject songButtonObj = Instantiate(songButtonPrefab, contentPanel);
        songButtonObj.transform.SetParent(contentPanel, false);

        SongData sd = song;
        if (SongDataLibrary.Instance != null && SongDataLibrary.Instance.IsLoaded)
        {
            sd = SongDataLibrary.Instance.GetSongDataByID(song.songID) ?? song;
        }
        int bestTotal = sd != null ? sd.personalRecord : song.personalRecord;
        int bestDiff = -1;
        string bestDiffName = "";
        if (sd != null)
        {
            sd.GetAbsoluteHighestScore(out bestTotal, out bestDiff, out bestDiffName);
        }

        SongButton songButton = songButtonObj.GetComponent<SongButton>();
        if (songButton != null)
        {
            songButton.thisSong_so = sd != null ? sd : song;
            int diffForDisplay = bestDiff >= 0 ? bestDiff : song.difficultyID;
            songButton.SetButtonData(song.songName, bestTotal, diffForDisplay, song.illustration, song.songID);
        }

        Image songImage = songButtonObj.GetComponentInChildren<Image>();
        TMP_Text[] texts = songButtonObj.GetComponentsInChildren<TMP_Text>();

        if (songImage != null && song.illustration != null)
        {
            songImage.sprite = song.illustration;
            songImage.enabled = true;
        }

        if (texts.Length >= 4)
        {
            texts[0].text = song.songName;
            texts[1].text = "Record : " + bestTotal;
            if (bestTotal <= 0)
            {
                texts[3].text = "";
            }
            else
            {
                texts[3].text = string.IsNullOrEmpty(bestDiffName) ? bestDiff.ToString() : bestDiffName;
            }
            texts[2].text = "SongID : " + song.songID.ToString();
        }

        Button button = songButtonObj.GetComponent<Button>();
        if (button != null && songButton != null)
            button.onClick.AddListener(() => songButton.OnSongButtonClick());
    }

    // helper to avoid hardcoding scene name string in delegate - keeps serializer-friendly field
    private string ui_Main_Scene_NAME() => ui_Main_Scene_Name;
}