using UnityEngine;
using UnityEditor;
using System.Collections.Generic;

public class AtlasAutoSplitter : EditorWindow
{
    Texture2D sourceTexture;
    Color32[] pixels;
    int width, height;
    bool[,] visited;

    [MenuItem("Tools/Atlas Auto Splitter")]
    static void Open()
    {
        GetWindow<AtlasAutoSplitter>("Atlas Splitter");
    }

    void OnGUI()
    {
        sourceTexture = (Texture2D)EditorGUILayout.ObjectField("图集 Texture2D", sourceTexture, typeof(Texture2D), false);

        if (sourceTexture == null)
            return;

        if (GUILayout.Button("开始自动分割"))
        {
            SplitAtlas();
        }
    }

    void SplitAtlas()
    {
        string path = AssetDatabase.GetAssetPath(sourceTexture);
        TextureImporter importer = AssetImporter.GetAtPath(path) as TextureImporter;

        if (importer == null)
        {
            Debug.LogError("无法获取 TextureImporter");
            return;
        }

        // 强制读取像素
        importer.isReadable = true;

        // 如果不是 Multiple，自动改
        if (importer.spriteImportMode != SpriteImportMode.Multiple)
        {
            importer.spriteImportMode = SpriteImportMode.Multiple;
        }

        // 应用修改并重新加载
        AssetDatabase.ImportAsset(path, ImportAssetOptions.ForceUpdate);
        sourceTexture = AssetDatabase.LoadAssetAtPath<Texture2D>(path);

        width = sourceTexture.width;
        height = sourceTexture.height;
        pixels = sourceTexture.GetPixels32();
        visited = new bool[width, height];

        List<SpriteMetaData> metas = new List<SpriteMetaData>();

        for (int y = height - 1; y >= 0; y--)
        {
            for (int x = 0; x < width; x++)
            {
                if (visited[x, y])
                    continue;

                if (!IsSolidPixel(x, y))
                {
                    visited[x, y] = true;
                    continue;
                }

                // 找到一个区域，开始 FloodFill
                Rect rect = FloodFill(x, y);

                SpriteMetaData meta = new SpriteMetaData();
                meta.name = $"sprite_{metas.Count}";
                // 修正坐标系：Unity 的 rect 原点在左下角
                meta.rect = new Rect(rect.x, height - rect.y - rect.height, rect.width, rect.height);
                meta.pivot = new Vector2(0.5f, 0.5f);
                meta.alignment = (int)SpriteAlignment.Center; // 必须设置
                metas.Add(meta);
            }
        }

        importer.spritesheet = metas.ToArray();

        // 确保写入并刷新
        EditorUtility.SetDirty(importer);
        AssetDatabase.WriteImportSettingsIfDirty(path);
        AssetDatabase.ImportAsset(path, ImportAssetOptions.ForceUpdate);
        AssetDatabase.Refresh();

        Debug.Log($"分割完成，共生成 {metas.Count} 个 Sprite");
    }


    bool IsSolidPixel(int x, int y)
    {
        Color32 c = pixels[y * width + x];
        return c.a > 10; // 透明度阈值
    }

    Rect FloodFill(int startX, int startY)
    {
        Queue<Vector2Int> q = new Queue<Vector2Int>();
        q.Enqueue(new Vector2Int(startX, startY));

        int minX = startX, maxX = startX;
        int minY = startY, maxY = startY;

        visited[startX, startY] = true;

        while (q.Count > 0)
        {
            Vector2Int p = q.Dequeue();
            int x = p.x;
            int y = p.y;

            // 更新边界
            if (x < minX) minX = x;
            if (x > maxX) maxX = x;
            if (y < minY) minY = y;
            if (y > maxY) maxY = y;

            // 四方向扩散
            TryAdd(x + 1, y, q);
            TryAdd(x - 1, y, q);
            TryAdd(x, y + 1, q);
            TryAdd(x, y - 1, q);
        }

        // 注意 Unity 的 rect 是左下角为原点
        return new Rect(minX, minY, maxX - minX + 1, maxY - minY + 1);
    }

    void TryAdd(int x, int y, Queue<Vector2Int> q)
    {
        if (x < 0 || x >= width || y < 0 || y >= height)
            return;

        if (visited[x, y])
            return;

        visited[x, y] = true;

        if (!IsSolidPixel(x, y))
            return;

        q.Enqueue(new Vector2Int(x, y));
    }
}