Explorer-Workbench/src/Explorer.App/ShellIconConverter.cs

using System.Collections.Concurrent;
using System.Globalization;
using System.IO;
using System.Runtime.InteropServices;
using System.Windows;
using System.Windows.Data;
using System.Windows.Interop;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using Explorer.Domain;
using Explorer.Presentation;

namespace Explorer.App;

public sealed class ShellIconConverter : IValueConverter
{
    public object? Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        var large = parameter is string p && p.Equals("large", StringComparison.OrdinalIgnoreCase);
        return value switch
        {
            FolderItemViewModel item => ShellIconCache.Get(item.FullPath, item.IsDirectory, large, item.MayHydrateOnRead),
            FileSystemItem fs => ShellIconCache.Get(fs.FullPath, fs.IsDirectory, large, AttributeFlags.MayHydrateOnRead(fs.Attributes)),
            string path => ShellIconCache.Get(path, Directory.Exists(path), large),
            _ => ShellIconCache.Get(null, true, large)
        };
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        => throw new NotSupportedException();
}

internal static class ShellIconCache
{
    private static readonly ConcurrentDictionary<string, ImageSource> Cache = new(StringComparer.OrdinalIgnoreCase);

    public static ImageSource Get(string? path, bool isDirectory, bool large = false, bool avoidHydration = false)
    {
        var key = (large ? "L:" : "S:") + (avoidHydration ? "A:" : "") + CacheKey(path, isDirectory);
        return Cache.GetOrAdd(key, _ => Load(path, isDirectory, large, avoidHydration));
    }

    private static string CacheKey(string? path, bool isDirectory)
    {
        if (string.IsNullOrWhiteSpace(path) || path == "This PC")
        {
            return isDirectory ? "dir:generic" : "file:generic";
        }

        if (path == LocationRoots.RecycleBin)
        {
            return "recycle";
        }

        if (isDirectory)
        {
            return PathRules.IsDriveRoot(path) || (path.Length <= 3 && path.Contains(':', StringComparison.Ordinal))
                ? "drive:" + path.TrimEnd('\\').ToUpperInvariant()
                : "dir:generic";
        }

        var ext = Path.GetExtension(path);
        if (ext.Equals(".exe", StringComparison.OrdinalIgnoreCase)
            || ext.Equals(".lnk", StringComparison.OrdinalIgnoreCase)
            || ext.Equals(".ico", StringComparison.OrdinalIgnoreCase)
            || ext.Equals(".dll", StringComparison.OrdinalIgnoreCase))
        {
            return "path:" + path;
        }

        return "ext:" + (string.IsNullOrEmpty(ext) ? ".file" : ext.ToLowerInvariant());
    }

    private static ImageSource Load(string? path, bool isDirectory, bool large, bool avoidHydration = false)
    {
        try
        {
            var info = new ShFileInfo();
            uint flags = ShgfiIcon | (large ? ShgfiLargeIcon : ShgfiSmallIcon);
            uint attrs = isDirectory ? FileAttributeDirectory : FileAttributeNormal;
            string psz;
            if (string.IsNullOrWhiteSpace(path) || path == "This PC")
            {
                psz = isDirectory ? "folder" : "file";
                flags |= ShgfiUseFileAttributes;
            }
            else if (path == LocationRoots.RecycleBin)
            {
                psz = @"::{645FF040-5081-101B-9F08-00AA002F954E}";
            }
            else if (isDirectory && PathRules.IsDriveRoot(path))
            {
                psz = PathRules.EnsureDirectoryTrailingSlashIfRoot(path);
            }
            else if (isDirectory)
            {
                psz = path;
                flags |= ShgfiUseFileAttributes;
            }
            else
            {
                psz = path;
                var ext = Path.GetExtension(path);
                if (avoidHydration
                    || !ext.Equals(".exe", StringComparison.OrdinalIgnoreCase)
                    && !ext.Equals(".lnk", StringComparison.OrdinalIgnoreCase)
                    && !ext.Equals(".ico", StringComparison.OrdinalIgnoreCase)
                    && File.Exists(path) == false)
                {
                    flags |= ShgfiUseFileAttributes;
                }
            }

            SHGetFileInfo(psz, attrs, ref info, (uint)Marshal.SizeOf<ShFileInfo>(), flags);
            if (info.hIcon == 0)
            {
                return Fallback();
            }

            try
            {
                var source = Imaging.CreateBitmapSourceFromHIcon(info.hIcon, Int32Rect.Empty, BitmapSizeOptions.FromEmptyOptions());
                source.Freeze();
                return source;
            }
            finally
            {
                DestroyIcon(info.hIcon);
            }
        }
        catch
        {
            return Fallback();
        }
    }

    private static ImageSource Fallback()
    {
        var bmp = BitmapSource.Create(16, 16, 96, 96, PixelFormats.Bgra32, null, new byte[16 * 16 * 4], 16 * 4);
        bmp.Freeze();
        return bmp;
    }

    private const uint ShgfiIcon = 0x100;
    private const uint ShgfiLargeIcon = 0x0;
    private const uint ShgfiSmallIcon = 0x1;
    private const uint ShgfiUseFileAttributes = 0x10;
    private const uint FileAttributeDirectory = 0x10;
    private const uint FileAttributeNormal = 0x80;

    [DllImport("shell32.dll", CharSet = CharSet.Unicode)]
    private static extern nint SHGetFileInfo(string pszPath, uint dwFileAttributes, ref ShFileInfo psfi, uint cbFileInfo, uint uFlags);

    [DllImport("user32.dll", SetLastError = true)]
    private static extern bool DestroyIcon(nint hIcon);

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    private struct ShFileInfo
    {
        public nint hIcon;
        public int iIcon;
        public uint dwAttributes;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
        public string szDisplayName;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 80)]
        public string szTypeName;
    }
}