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

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";

    // 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;

    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(
        () => SceneManager.LoadScene(ui_Main_Scene_NAME(), LoadSceneMode.Single));
        // Do not populate the song list at start. DLC buttons will request songs when clicked.
    }

    // 显示所有歌曲 (kept for manual use)
    public void DisplaySongs()
    {
        ClearSongList();

        foreach (SongData song in songList.songs)
        {
            InstantiateSongButton(song);
        }

        if (restoreCoroutine != null) StopCoroutine(restoreCoroutine);
        restoreCoroutine = StartCoroutine(RestoreSelectedSongNextFrame());
    }

    // Instantiate from a provided list (used by dlcButton to show DLC songs)
    public void DisplaySongsFromList(List<SongData> list)
    {
        ClearSongList();

        if (list == null) return;
        foreach (var song in list)
            InstantiateSongButton(song);

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

    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);

        SongButton songButton = songButtonObj.GetComponent<SongButton>();
        if (songButton != null)
        {
            songButton.SetButtonData(song.songName, song.personalRecord, song.difficultyID, 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 : " + song.personalRecord;
            texts[3].text = "" + song.difficultyID;
            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;
}