Feature: Add disk based thumbnail caching system

src/Files.App/Data/Contracts/IGeneralSettingsService.cs

@@ -316,6 +316,15 @@ public interface IGeneralSettingsService : IBaseSettingsService, INotifyProperty
 		bool ShowFilterHeader { get; set; }
 
 		/// <summary>
+		/// Gets or sets a value indicating whether thumbnail cache should be enabled.
+		/// </summary>
+		bool EnableThumbnailCache { get; set; }
+
+		/// <summary>
+		/// Gets or sets the thumbnail cache size limit in MB.
+		/// </summary>
+		double ThumbnailCacheSizeLimit { get; set; }
+
 		/// Gets or sets a value indicating whether smooth scrolling is enabled.
 		/// </summary>
 		bool EnableSmoothScrolling { get; set; }

src/Files.App/Data/Contracts/IThumbnailCache.cs

@@ -0,0 +1,48 @@
+// Copyright (c) Files Community
+// Licensed under the MIT License.
+
+namespace Files.App.Data.Contracts
+{
+	/// <summary>
+	/// Stores and retrieves cached thumbnails.
+	/// </summary>
+	public interface IThumbnailCache
+	{
+		/// <summary>
+		/// Retrieves a cached thumbnail.
+		/// </summary>
+		/// <returns>Thumbnail bytes, or null if not cached.</returns>
+		Task<byte[]?> GetAsync(string path, int size, IconOptions options, CancellationToken ct);
+
+		/// <summary>
+		/// Stores a thumbnail in the cache.
+		/// </summary>
+		Task SetAsync(string path, int size, IconOptions options, byte[] thumbnail, CancellationToken ct);
+
+		/// <summary>
+		/// Gets the current cache size in bytes.
+		/// </summary>
+		Task<long> GetSizeAsync();
+
+		/// <summary>
+		/// Reduces cache size to the specified target in bytes.
+		/// </summary>
+		Task EvictToSizeAsync(long targetSizeBytes);
+
+		/// <summary>
+		/// Removes all cached thumbnails.
+		/// </summary>
+		Task ClearAsync();
+
+		/// <summary>
+		/// Retrieves a cached icon from the in-memory icon cache.
+		/// </summary>
+		/// <returns>Icon bytes, or null if not cached.</returns>
+		byte[]? GetIcon(string extension, int size);
+
+		/// <summary>
+		/// Stores an icon in the in-memory icon cache.
+		/// </summary>
+		void SetIcon(string extension, int size, byte[] iconData);
+	}
+}

src/Files.App/Data/Contracts/IThumbnailGenerator.cs

@@ -0,0 +1,27 @@
+// Copyright (c) Files Community
+// Licensed under the MIT License.
+
+namespace Files.App.Data.Contracts
+{
+	/// <summary>
+	/// Generates thumbnails for specific file types.
+	/// </summary>
+	public interface IThumbnailGenerator
+	{
+		/// <summary>
+		/// Gets the file extensions this generator supports.
+		/// </summary>
+		IEnumerable<string> SupportedTypes { get; }
+
+		/// <summary>
+		/// Generates a thumbnail for the specified path.
+		/// </summary>
+		/// <returns>Thumbnail bytes, or null if generation fails.</returns>
+		Task<byte[]?> GenerateAsync(
+			string path,
+			int size,
+			bool isFolder,
+			IconOptions options,
+			CancellationToken ct);
+	}
+}

src/Files.App/Data/Contracts/IThumbnailService.cs

@@ -0,0 +1,53 @@
+// Copyright (c) Files Community
+// Licensed under the MIT License.
+
+namespace Files.App.Data.Contracts
+{
+	/// <summary>
+	/// Provides thumbnail retrieval and cache management.
+	/// </summary>
+	public interface IThumbnailService
+	{
+		/// <summary>
+		/// Gets a thumbnail for the specified path.
+		/// </summary>
+		/// <returns>Thumbnail bytes, or null if unavailable.</returns>
+		Task<byte[]?> GetThumbnailAsync(
+			string path,
+			int size,
+			bool isFolder,
+			IconOptions options = IconOptions.None,
+			CancellationToken ct = default);
+
+		/// <summary>
+		/// Gets a cached thumbnail without calling the Shell API.
+		/// Returns null if not found in the cache.
+		/// </summary>
+		Task<byte[]?> GetCachedThumbnailAsync(
+			string path,
+			int size,
+			bool isFolder,
+			IconOptions options,
+			CancellationToken ct = default);
+
+		/// <summary>
+		/// Registers a thumbnail generator.
+		/// </summary>
+		void RegisterGenerator(IThumbnailGenerator generator);
+
+		/// <summary>
+		/// Clears all cached thumbnails.
+		/// </summary>
+		Task ClearCacheAsync();
+
+		/// <summary>
+		/// Gets the current cache size in bytes.
+		/// </summary>
+		Task<long> GetCacheSizeAsync();
+
+		/// <summary>
+		/// Reduces cache size to the specified target in bytes.
+		/// </summary>
+		Task EvictCacheAsync(long targetSizeBytes);
+	}
+}

src/Files.App/Helpers/Application/AppLifecycleHelper.cs

@@ -3,6 +3,8 @@
 
 using Files.App.Helpers.Application;
 using Files.App.Services.SizeProvider;
+using Files.App.Services.Thumbnails;
+using Files.App.Services.Thumbnails.Generators;
 using Files.App.Utils.Logger;
 using Files.App.ViewModels.Settings;
 using Microsoft.Extensions.DependencyInjection;
@@ -263,6 +265,9 @@ public static IHost ConfigureHost()
 					.AddSingleton<IStorageArchiveService, StorageArchiveService>()
 					.AddSingleton<IStorageSecurityService, StorageSecurityService>()
 					.AddSingleton<IWindowsCompatibilityService, WindowsCompatibilityService>()
+					.AddSingleton<IThumbnailCache, ThumbnailCache>()
+					.AddSingleton<IThumbnailGenerator, ShellApiThumbnailGenerator>()
+					.AddSingleton<IThumbnailService, ThumbnailService>()
 					// ViewModels
 					.AddSingleton<MainPageViewModel>()
 					.AddSingleton<InfoPaneViewModel>()

src/Files.App/Services/Settings/GeneralSettingsService.cs

@@ -387,13 +387,24 @@ public bool ShowFilterHeader
 			set => Set(value);
 		}
 
-		/// <inheritdoc/>
+		public bool EnableThumbnailCache
+    {
+			get => Get(true);
+			set => Set(value);
+		}
+
 		public bool EnableSmoothScrolling
 		{
 			get => Get(true);
 			set => Set(value);
 		}
 
+		public double ThumbnailCacheSizeLimit
+		{
+			get => Get(512d);
+			set => Set(value);
+		}
+
 		protected override void RaiseOnSettingChangedEvent(object sender, SettingChangedEventArgs e)
 		{
 			base.RaiseOnSettingChangedEvent(sender, e);

src/Files.App/Services/Thumbnails/Generators/ShellApiThumbnailGenerator.cs

@@ -0,0 +1,31 @@
+// Copyright (c) Files Community
+// Licensed under the MIT License.
+
+using Microsoft.Extensions.Logging;
+
+namespace Files.App.Services.Thumbnails.Generators
+{
+	public sealed class ShellApiThumbnailGenerator : IThumbnailGenerator
+	{
+		private readonly ILogger _logger;
+
+		public IEnumerable<string> SupportedTypes => ["*"];
+
+		public ShellApiThumbnailGenerator(ILogger<ShellApiThumbnailGenerator> logger)
+		{
+			_logger = logger;
+		}
+
+		public async Task<byte[]?> GenerateAsync(
+			string path,
+			int size,
+			bool isFolder,
+			IconOptions options,
+			CancellationToken ct)
+		{
+			return await STATask.Run(() =>
+				Win32Helper.GetIcon(path, size, isFolder, options),
+				_logger);
+		}
+	}
+}