using System.IO;
using UnityEngine;
using UnityEngine.SceneManagement;

public partial class MeshPainter
{
    // --- Persistence: save the painted maps to disk and reload them next session ---

    [Header("Persistence")]
    [Tooltip("Save the painted maps to disk on quit / play-stop and reload them on the next " +
             "start, so the painting persists across sessions. Off = paint is volatile (as before).")]
    public bool persistPaint = true;

    [Tooltip("Save file identifier. Empty = derived from the active scene + object name. Set " +
             "explicitly to keep a save stable across object renames or to share one save.")]
    public string saveId = "";

    // Raw, bit-exact map dump: 'CHMP' magic + version + width + height + map count, then each
    // map's canonical Color32 bytes. Raw (not PNG) avoids any sRGB/alpha-premultiply ambiguity
    // and round-trips the exact canonical bytes ReadCanonical produces.
    private const uint PaintFileMagic = 0x504D4843; // 'CHMP' little-endian
    private const int PaintFileVersion = 1;

    private bool _savedOnTeardown; // guards against a double save across OnApplicationQuit + OnDestroy

    private static string PaintSaveDir => Path.Combine(Application.persistentDataPath, "MeshPaint");

    private string PaintSavePath()
    {
        string key = string.IsNullOrEmpty(saveId)
            ? SanitizeKey(SceneManager.GetActiveScene().name + "_" + gameObject.name)
            : SanitizeKey(saveId);
        return Path.Combine(PaintSaveDir, key + ".paint");
    }

    private static string SanitizeKey(string s)
    {
        foreach (char c in Path.GetInvalidFileNameChars()) s = s.Replace(c, '_');
        return s.Replace(' ', '_');
    }

    /// <summary>Reads all maps from the active backend (canonical layout) and writes them to the save file.</summary>
    public void SavePaint()
    {
        if (!persistPaint || !_setupValid) return;

        try
        {
            Directory.CreateDirectory(PaintSaveDir);
            int n = textureSize * textureSize;

            using (var fs = new FileStream(PaintSavePath(), FileMode.Create, FileAccess.Write))
            using (var w = new BinaryWriter(fs))
            {
                w.Write(PaintFileMagic);
                w.Write(PaintFileVersion);
                w.Write(textureSize);
                w.Write(textureSize);
                w.Write(MAP_COUNT);

                var bytes = new byte[n * 4];
                for (int mi = 0; mi < MAP_COUNT; mi++)
                {
                    Color32[] px = ReadCanonical(mi);
                    int count = Mathf.Min(n, px.Length);
                    for (int i = 0; i < count; i++)
                    {
                        int o = i * 4;
                        bytes[o] = px[i].r;
                        bytes[o + 1] = px[i].g;
                        bytes[o + 2] = px[i].b;
                        bytes[o + 3] = px[i].a;
                    }
                    w.Write(bytes, 0, count * 4);
                }
            }
        }
        catch (System.Exception e)
        {
            Debug.LogWarning($"[MeshPainter] Saving paint failed: {e.Message}", this);
        }
    }

    /// <summary>
    /// Loads the saved maps in canonical layout for seeding, or null if none / incompatible.
    /// Per-map null entries are tolerated by both backends (they fall back to the material seed).
    /// </summary>
    private Color32[][] LoadPaintMaps()
    {
        if (!persistPaint) return null;

        string path = PaintSavePath();
        if (!File.Exists(path)) return null;

        try
        {
            using (var fs = new FileStream(path, FileMode.Open, FileAccess.Read))
            using (var r = new BinaryReader(fs))
            {
                if (r.ReadUInt32() != PaintFileMagic) return null;
                int ver = r.ReadInt32();
                int w = r.ReadInt32();
                int h = r.ReadInt32();
                int maps = r.ReadInt32();

                // Resolution / version change -> ignore the save rather than smear mismatched
                // data; the brush re-seeds from the material instead.
                if (ver != PaintFileVersion || w != textureSize || h != textureSize)
                {
                    Debug.LogWarning($"[MeshPainter] Saved paint ignored (got {w}x{h} v{ver}, expected " +
                                     $"{textureSize}x{textureSize} v{PaintFileVersion}). Re-seeding from material.", this);
                    return null;
                }

                int n = textureSize * textureSize;
                var result = new Color32[MAP_COUNT][];
                int load = Mathf.Min(maps, MAP_COUNT);
                for (int mi = 0; mi < load; mi++)
                {
                    byte[] raw = r.ReadBytes(n * 4);
                    if (raw.Length != n * 4) break; // truncated file -> remaining maps stay seeded

                    var px = new Color32[n];
                    for (int i = 0; i < n; i++)
                    {
                        int o = i * 4;
                        px[i] = new Color32(raw[o], raw[o + 1], raw[o + 2], raw[o + 3]);
                    }
                    result[mi] = px;
                }
                return result;
            }
        }
        catch (System.Exception e)
        {
            Debug.LogWarning($"[MeshPainter] Loading paint failed: {e.Message}", this);
            return null;
        }
    }

    /// <summary>Saves once during teardown (OnApplicationQuit and OnDestroy both call this; only the first writes).</summary>
    private void SavePaintOnTeardown()
    {
        if (_savedOnTeardown) return;
        _savedOnTeardown = true;
        SavePaint();
    }

    /// <summary>Deletes this painter's save file (next start re-seeds from the material). Editor convenience.</summary>
    [ContextMenu("Clear Saved Paint")]
    public void ClearSavedPaint()
    {
        try
        {
            string path = PaintSavePath();
            if (File.Exists(path)) File.Delete(path);
            Debug.Log($"[MeshPainter] Cleared saved paint: {path}", this);
        }
        catch (System.Exception e)
        {
            Debug.LogWarning($"[MeshPainter] Clearing saved paint failed: {e.Message}", this);
        }
    }
}