using System.Buffers.Binary;
using System.Text;

namespace FluidExplorer.Services.Shell;

/// <summary>回收站里的一条记录（从 $I 元数据文件解析，含原始路径）。</summary>
public sealed record RecycleBinEntry(
    string RecyclePath,
    string OriginalPath,
    long Size,
    DateTime DeletedUtc,
    string VolumeRoot)
{
    public string Name => Services.FileSystem.PathHelper.GetName(OriginalPath);
    public string OriginalDirectory => Services.FileSystem.PathHelper.GetParent(OriginalPath);
    public bool IsDirectory => Size == 0 && OriginalPath.Length > 0 && !Path.HasExtension(OriginalPath);
}

/// <summary>
/// 直接读取各卷的 $Recycle.Bin\&lt;SID&gt;\$I* 元数据文件，得到回收站内容与原始路径。
/// 这样"还原/彻底删除"都能由本程序完成（不依赖系统弹窗），也支持一步撤销。
/// </summary>
public static class RecycleBinView
{
    public static async Task<IReadOnlyList<RecycleBinEntry>> EnumerateAsync(CancellationToken cancellationToken)
        => await Task.Run(() => Enumerate(cancellationToken), cancellationToken).ConfigureAwait(false);

    public static IReadOnlyList<RecycleBinEntry> Enumerate(CancellationToken cancellationToken = default)
    {
        var results = new List<RecycleBinEntry>();
        foreach (var drive in DriveInfo.GetDrives())
        {
            cancellationToken.ThrowIfCancellationRequested();
            try
            {
                if (!drive.IsReady || drive.DriveType != DriveType.Fixed) continue;
                var binRoot = Path.Combine(drive.Name, "$Recycle.Bin");
                if (!Directory.Exists(binRoot)) continue;

                foreach (var sidDir in Directory.EnumerateDirectories(binRoot))
                {
                    cancellationToken.ThrowIfCancellationRequested();
                    try
                    {
                        foreach (var metaFile in Directory.EnumerateFiles(sidDir, "$I*"))
                        {
                            cancellationToken.ThrowIfCancellationRequested();
                            var entry = TryParse(metaFile, drive.Name);
                            if (entry is not null) results.Add(entry);
                        }
                    }
                    catch
                    {
                        // 其他用户的回收站目录通常无权限，跳过
                    }
                }
            }
            catch
            {
                // 卷不可读时跳过
            }
        }

        return results;
    }

    /// <summary>解析单个 $I 元数据文件。</summary>
    public static RecycleBinEntry? TryParse(string metaFilePath, string volumeRoot)
    {
        try
        {
            var bytes = File.ReadAllBytes(metaFilePath);
            if (bytes.Length < 24) return null;

            var version = BinaryPrimitives.ReadInt64LittleEndian(bytes.AsSpan(0, 8));
            var size = BinaryPrimitives.ReadInt64LittleEndian(bytes.AsSpan(8, 8));
            var fileTime = BinaryPrimitives.ReadInt64LittleEndian(bytes.AsSpan(16, 8));
            var deleted = fileTime > 0 ? DateTime.FromFileTimeUtc(fileTime) : DateTime.MinValue;

            string originalPath;
            if (version >= 2 && bytes.Length >= 28)
            {
                var length = BinaryPrimitives.ReadInt32LittleEndian(bytes.AsSpan(24, 4));
                if (length <= 0 || 28 + length * 2 > bytes.Length) return null;
                originalPath = Encoding.Unicode.GetString(bytes, 28, length * 2).TrimEnd('\0');
            }
            else if (version == 1)
            {
                // 旧格式：路径固定在 0x2C 偏移处的 260 个宽字符
                if (bytes.Length < 0x2C + 520) return null;
                originalPath = Encoding.Unicode.GetString(bytes, 0x2C, 520).TrimEnd('\0');
            }
            else
            {
                return null;
            }

            if (string.IsNullOrWhiteSpace(originalPath)) return null;

            var fileName = Path.GetFileName(metaFilePath);
            var recyclePath = Path.Combine(Path.GetDirectoryName(metaFilePath)!, "$R" + fileName[2..]);
            return new RecycleBinEntry(recyclePath, originalPath, Math.Max(0, size), deleted, volumeRoot);
        }
        catch
        {
            return null;
        }
    }
}