import 'dart:io';


class Vips {
  String? vipsExecuteFile;
  final String cacheDir;

  Vips({this.vipsExecuteFile, required this.cacheDir});

  /// 生成图片预览（WebP 格式）
  ///
  /// [imgPath] 原图路径
  /// [w] 预览图宽度（可选）
  /// [h] 预览图高度（可选）
  ///
  /// 如果同时指定 [w] 和 [h]，图片将按比例缩放以适应指定尺寸
  Future<File> generatePreview(String imgPath, {int? w, int? h}) async {
    // 生成缓存文件名：包含原图 hash 和尺寸信息
    final baseName = imgPath.hashCode.toString();
    final sizeSuffix = _buildSizeSuffix(w, h);
    final imgOut = "$cacheDir/preview/$baseName$sizeSuffix.webp";
    final outFile = File(imgOut);

    // 缓存命中：直接返回已存在的预览图
    if (outFile.existsSync()) {
      return outFile;
    }

    // 确保缓存目录存在
    await outFile.parent.create(recursive: true);

    // 构建 vips 命令参数
    if (w != null || h != null) {
      final thumbnailArgs = <String>[
        "thumbnail",
        imgPath,
        imgOut,
        w?.toString() ?? "0",
        "--height",
        h?.toString() ?? "0",
      ];

      final thumbnailResult = await Process.run("vips", thumbnailArgs);
      if (thumbnailResult.exitCode != 0) {
        print(thumbnailResult.stderr);
        throw Exception("vips thumbnail failed!");
      }
      return outFile;
    } else {
      // 不缩放，直接转换为 WebP 格式
      final args = <String>[
        "webpsave",
        imgPath,
        imgOut,
        "--Q",
        "80",
        "--effort",
        "6",
        "--smart-subsample",
      ];

      final result = await Process.run("vips", args);
      if (result.exitCode == 0) {
        return outFile;
      }
      print(result.stderr);
      throw Exception("vips image transcode failed!");
    }
  }

  /// 构建尺寸后缀
  ///
  /// 例如：
  /// - w=200, h=150 => "_200x150"
  /// - w=200, h=null => "_200x0"
  /// - w=null, h=150 => "_0x150"
  /// - w=null, h=null => ""
  String _buildSizeSuffix(int? w, int? h) {
    if (w == null && h == null) {
      return "";
    }
    return "_${w ?? 0}x${h ?? 0}";
  }
}