Libation/Source/LibationFileManager/WindowsDirectory.cs

using System;
using System.Threading;

namespace LibationFileManager;

public static class WindowsDirectory
{
	const int FolderIconMaxAttempts = 5;

	public static void SetCoverAsFolderIcon(string? pictureId, string directory, CancellationToken cancellationToken)
    {
        //Currently only works for Windows and macOS
        if (!Configuration.Instance.UseCoverAsFolderIcon)
			return;
		if (string.IsNullOrEmpty(pictureId))
		{
			Serilog.Log.Logger.Warning("No picture ID provided to set cover art as folder icon. {@DebugInfo}", new { directory });
			return;
        }

        // Load JPEG bytes from Images cache (or download). Prefer bytes → ICO so we never depend on a
        // path that might not exist when Amazon omits Content-Length or another downloader left a stale cache entry.

        for (var attempt = 1; attempt <= FolderIconMaxAttempts; attempt++)
		{
			cancellationToken.ThrowIfCancellationRequested();

			try
			{
				var jpegBytes = PictureStorage.GetPictureSynchronously(new(pictureId, PictureSize._300x300), cancellationToken);
				if (jpegBytes.Length == 0)
				{
					if (attempt < FolderIconMaxAttempts)
					{
						Serilog.Log.Logger.Debug("Folder icon: empty 300x300 image on attempt {Attempt}/{Max}; retrying after delay. {@DebugInfo}", attempt, FolderIconMaxAttempts, new { directory, pictureId });
						DelayBetweenFolderIconRetries(cancellationToken, attempt);
						continue;
					}

					break;
				}

				InteropFactory.Create().SetFolderIcon(imageJpegBytes: jpegBytes, directory: directory);
				return;
			}
			catch (Exception ex)
			{
				if (attempt < FolderIconMaxAttempts)
				{
					Serilog.Log.Logger.Debug(ex, "Folder icon: attempt {Attempt}/{Max} failed; retrying after delay. {@DebugInfo}", attempt, FolderIconMaxAttempts, new { directory, pictureId });
					DelayBetweenFolderIconRetries(cancellationToken, attempt);
					continue;
				}

				if (TrySetFolderIconUsingPictureSize(pictureId, directory, PictureSize.Native, cancellationToken))
				{
					Serilog.Log.Logger.Information(
						"Set Explorer folder icon using full-size cover after 300x300 failed (decode, ICO conversion, or writing desktop.ini/Icon.ico). {@DebugInfo}",
						new { directory, pictureId });
					return;
				}

				Serilog.Log.Logger.Error(ex,
					"Could not set Explorer folder icon after {MaxAttempts} attempts (decode, ICO conversion, or writing desktop.ini/Icon.ico failed). The audiobook download itself should still be fine; try liberating again, or check folder permissions if the library is on removable media. {@DebugInfo}",
					FolderIconMaxAttempts, new { directory, pictureId });
				TryDeleteFolderIcon(directory);
				return;
			}
		}

		// 300x300 never returned usable bytes — Native is a separate CDN URL and is often already cached by DownloadCoverArt in the same session.
		if (TrySetFolderIconUsingPictureSize(pictureId, directory, PictureSize.Native, cancellationToken))
		{
			Serilog.Log.Logger.Information(
				"Set Explorer folder icon using full-size cover after 300x300 was empty or missing. {@DebugInfo}",
				new { directory, pictureId });
			return;
		}

		Serilog.Log.Logger.Warning(
			"Could not set Explorer folder icon: neither 300x300 nor full-size cover became available. The audiobook download itself is unaffected. Check your network to Amazon images, disk space under Libation's Images folder, or try liberating again. {@DebugInfo}",
			new { directory, pictureId });
		TryDeleteFolderIcon(directory);
	}

	static bool TrySetFolderIconUsingPictureSize(string pictureId, string directory, PictureSize size, CancellationToken cancellationToken)
	{
		cancellationToken.ThrowIfCancellationRequested();
		try
		{
			var jpegBytes = PictureStorage.GetPictureSynchronously(new(pictureId, size), cancellationToken);
			if (jpegBytes.Length == 0)
				return false;
			InteropFactory.Create().SetFolderIcon(imageJpegBytes: jpegBytes, directory: directory);
			return true;
		}
		catch (Exception ex)
		{
			Serilog.Log.Logger.Debug(ex, "Folder icon: could not set using {PictureSize}. {@DebugInfo}", size, new { directory, pictureId });
			return false;
		}
	}

	static void DelayBetweenFolderIconRetries(CancellationToken cancellationToken, int attemptAfterFailure)
	{
		// 100, 200, 400, 800 ms; bounded backoff without Task.Delay allocation on hot path
		var ms = 100 * (1 << (attemptAfterFailure - 1));
		if (ms > 0)
			cancellationToken.WaitHandle.WaitOne(ms);
	}

	static void TryDeleteFolderIcon(string directory)
	{
		try
		{
			InteropFactory.Create().DeleteFolderIcon(directory);
		}
		catch (Exception ex)
		{
			Serilog.Log.Logger.Error(ex, "Error rolling back folder icon files. {@DebugInfo}", new { directory });
		}
	}
}