Feature: Prevent setting cloud placeholder files as lock screen wallpaper

Author: seer-by-sentry[bot]

src/Files.App/Services/Windows/WindowsWallpaperService.cs

@@ -1,6 +1,9 @@
 // Copyright (c) Files Community
 // Licensed under the MIT License.
 
+using System.IO;
+using Vanara.PInvoke;
+using Vanara.Windows.Shell;
 using Windows.Storage;
 using Windows.System.UserProfile;
 using Windows.Win32;
@@ -13,6 +16,8 @@ namespace Files.App.Services
 	/// <inheritdoc cref="IWindowsWallpaperService"/>
 	public sealed class WindowsWallpaperService : IWindowsWallpaperService
 	{
+		private static readonly Ole32.PROPERTYKEY PKEY_FilePlaceholderStatus = new Ole32.PROPERTYKEY(new Guid("B2F9B9D6-FEC4-4DD5-94D7-8957488C807B"), 2);
+		private const uint PS_CLOUDFILE_PLACEHOLDER = 8;
 		/// <inheritdoc/>
 		public unsafe void SetDesktopWallpaper(string szPath)
 		{
@@ -69,8 +74,38 @@ public unsafe void SetDesktopSlideshow(string[] aszPaths)
 		/// <inheritdoc/>
 		public async Task SetLockScreenWallpaper(string szPath)
 		{
+			// Verify the file exists on disk
+			if (!File.Exists(szPath))
+				throw new FileNotFoundException("The specified file does not exist.", szPath);
+
+			// Check if the file is a cloud placeholder (online-only file)
+			if (IsCloudPlaceholder(szPath))
+				throw new InvalidOperationException("The file is stored in the cloud and is not available offline. Please download the file before setting it as a wallpaper.");
+
 			IStorageFile sourceFile = await StorageFile.GetFileFromPathAsync(szPath);
 			await LockScreen.SetImageFileAsync(sourceFile);
 		}
+
+		/// <summary>
+		/// Checks if the file is a cloud placeholder (online-only file).
+		/// </summary>
+		/// <param name="path">The path to the file.</param>
+		/// <returns>True if the file is a cloud placeholder; otherwise, false.</returns>
+		private static bool IsCloudPlaceholder(string path)
+		{
+			try
+			{
+				using var shi = new ShellItem(path);
+				if (shi.Properties.TryGetValue<uint>(PKEY_FilePlaceholderStatus, out var value) && value == PS_CLOUDFILE_PLACEHOLDER)
+					return true;
+			}
+			catch
+			{
+				// If we can't determine the placeholder status, assume it's not a placeholder
+				// and let the subsequent StorageFile.GetFileFromPathAsync call handle any errors
+			}
+
+			return false;
+		}
 	}
 }