Improved MarkdownViewer

#### Features
- Uses the latest [github-markdown.css](https://github.com/sindresorhus/github-markdown-css/blob/main/github-markdown.css) file that contains styling support for both dark and light mode.
- Table of Contents has an improved design, and:
	- The width can be resized.
	- TOC headings are automatically highlighted to help track your position in the file.
- Improved fullscreen layout based on Github.com behavior.
- External links clicked will open in default browser instead of doing nothing.
- Uses [markdownItAnchor](https://github.com/valeriangalliat/markdown-it-anchor) to allow heading anchor links in the file to work.
- Uses [highlight.js](https://github.com/highlightjs/highlight.js) to provide syntax highlighting to codeblocks.
#### Changes
- Made changes to allow the `md2html.html` file to use relative file imports for better maintainability.
- MarkdownViewer can now easily be customized by users by modifying files in `<Quicklook data folder>/QuickLook.Plugin.MarkdownViewer/`
- Caching and `localStorage` is now supported thanks to these changes.
- Prevent default behavior of spacebar scrolling the page, while we use spacebar to dismiss the preview.
- Sets `WebView` `DefaultBackgroundColor` to prevent white flash in dark mode. After the page has loaded, sets `DefaultBackgroundColor` back to white to have the expected default behavior on HTML pages that don't specify any background color.
#### Clean up
- Removed the need for `jQuery`.
- Removed old polyfill code.

QuickLook.Plugin/QuickLook.Plugin.HtmlViewer/WebpagePanel.cs

@@ -1,4 +1,4 @@
-// Copyright © 2021 Paddy Xu and Frank Becker
+// Copyright © 2021 Paddy Xu and Frank Becker
 //
 // This file is part of QuickLook program.
 //
@@ -17,6 +17,7 @@
 
 using System;
 using System.Diagnostics;
+using System.Drawing;
 using System.IO;
 using System.Reflection;
 using System.Windows;
@@ -29,8 +30,8 @@ namespace QuickLook.Plugin.HtmlViewer
 {
     public class WebpagePanel : UserControl
     {
-        private Uri _currentUri;
-        private WebView2 _webView;
+        public Uri _currentUri;
+        public WebView2 _webView;
 
         public WebpagePanel()
         {
@@ -44,10 +45,12 @@ namespace QuickLook.Plugin.HtmlViewer
                 {
                     CreationProperties = new CoreWebView2CreationProperties
                     {
-                        UserDataFolder = Path.Combine(SettingHelper.LocalDataPath, @"WebView2_Data\\")
-                    }
+                        UserDataFolder = Path.Combine(SettingHelper.LocalDataPath, @"WebView2_Data\\"),
+                    },
+                    DefaultBackgroundColor = OSThemeHelper.AppsUseDarkTheme() ? Color.FromArgb(255, 32, 32, 32) : Color.White, // Prevent white flash in dark mode
                 };
                 _webView.NavigationStarting += NavigationStarting_CancelNavigation;
+                _webView.NavigationCompleted += WebView_NavigationCompleted;
                 Content = _webView;
             }
         }
@@ -83,6 +86,11 @@ namespace QuickLook.Plugin.HtmlViewer
             if (newUri != _currentUri) e.Cancel = true;
         }
 
+        private void WebView_NavigationCompleted(object sender, CoreWebView2NavigationCompletedEventArgs e)
+        {
+            _webView.DefaultBackgroundColor = Color.White; // Reset to white after page load to match expected default behavior
+        }
+
         public void Dispose()
         {
             _webView?.Dispose();

QuickLook.Plugin/QuickLook.Plugin.MarkdownViewer/Plugin.cs

@@ -1,4 +1,4 @@
-// Copyright © 2017 Paddy Xu
+// Copyright © 2017 Paddy Xu
 // 
 // This file is part of QuickLook program.
 // 
@@ -16,12 +16,17 @@
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 using System;
+using System.Diagnostics;
 using System.IO;
 using System.Linq;
 using System.Net;
+using System.Reflection;
+using System.Runtime.InteropServices;
 using System.Text;
 using System.Windows;
 using System.Windows.Threading;
+using Microsoft.Web.WebView2.Core;
+using QuickLook.Common.Helpers;
 using QuickLook.Common.Plugin;
 using QuickLook.Plugin.HtmlViewer;
 using UtfUnknown;
@@ -30,17 +35,90 @@ namespace QuickLook.Plugin.MarkdownViewer
 {
     public class Plugin : IViewer
     {
-        private WebpagePanel _panel;
+        private WebpagePanel? _panel;
+        private static string _resourcePath;
+        private static readonly string ResourcePrefix = "QuickLook.Plugin.MarkdownViewer.Resources.";
+        private string? _currentHtmlPath;
+
+        private static bool OverrideFilesInDevelopment => true && Debugger.IsAttached; // Debug setting
+
+        static Plugin()
+        {
+            // Set up resource path in AppData
+            _resourcePath = Path.Combine(SettingHelper.LocalDataPath, "QuickLook.Plugin.MarkdownViewer");
+        }
 
         public int Priority => 0;
 
         public void Init()
         {
+            // Create directory if it doesn't exist
+            if (!Directory.Exists(_resourcePath) || OverrideFilesInDevelopment)
+            {
+                Directory.CreateDirectory(_resourcePath);
+                ExtractResources();
+            }
+
+            // Clean up any temporary HTML files if QuickLook was forcibly terminated
+            try
+            {
+                var tempFiles = Directory.GetFiles(_resourcePath, "temp_*.html");
+                foreach (var file in tempFiles)
+                {
+                    try
+                    {
+                        File.Delete(file);
+                    }
+                    catch (IOException) { } // Ignore deletion errors
+                }
+            }
+            catch (Exception ex)
+            {
+                Debug.WriteLine($"Failed to clean up temporary HTML files: {ex.Message}");
+            }
+        }
+
+        private void ExtractResources()
+        {
+            var assembly = Assembly.GetExecutingAssembly();
+            var resourceNames = assembly.GetManifestResourceNames();
+
+            foreach (var resourceName in resourceNames)
+            {
+                if (!resourceName.StartsWith(ResourcePrefix)) continue;
+
+                var relativePath = resourceName.Substring(ResourcePrefix.Length);
+                if (relativePath.Equals("resources", StringComparison.OrdinalIgnoreCase)) continue; // Skip 'resources' binary file
+
+                var targetPath = Path.Combine(_resourcePath, relativePath.Replace('/', Path.DirectorySeparatorChar));
+
+                // Create directory if it doesn't exist
+                var directory = Path.GetDirectoryName(targetPath);
+                if (directory != null)
+                    Directory.CreateDirectory(directory);
+
+                // Extract the resource (skip if it already exists, unless in debug mode)
+                if (File.Exists(targetPath) && !OverrideFilesInDevelopment)
+                    continue;
+
+                using (var resourceStream = assembly.GetManifestResourceStream(resourceName))
+                using (var fileStream = File.Create(targetPath))
+                {
+                    resourceStream?.CopyTo(fileStream);
+                }
+            }
+
+            // Verify that md2html.html was extracted
+            var htmlPath = Path.Combine(_resourcePath, "md2html.html");
+            if (!File.Exists(htmlPath))
+            {
+                throw new FileNotFoundException($"Required template file md2html.html not found in resources. Available resources: {string.Join(", ", resourceNames)}");
+            }
         }
 
         public bool CanHandle(string path)
         {
-            return !Directory.Exists(path) && new[] {".md", ".rmd", ".markdown"}.Any(path.ToLower().EndsWith);
+            return !Directory.Exists(path) && new[] { ".md", ".rmd", ".markdown" }.Any(path.ToLower().EndsWith);
         }
 
         public void Prepare(string path, ContextObject context)
@@ -54,29 +132,180 @@ namespace QuickLook.Plugin.MarkdownViewer
             context.ViewerContent = _panel;
             context.Title = Path.GetFileName(path);
 
-            _panel.NavigateToHtml(GenerateMarkdownHtml(path));
+            var htmlPath = GenerateMarkdownHtml(path);
+            _panel.NavigateToFile(htmlPath);
             _panel.Dispatcher.Invoke(() => { context.IsBusy = false; }, DispatcherPriority.Loaded);
+
+            _panel._webView.NavigationStarting += NavigationStarting_CancelNavigation;
+        }
+
+        private void NavigationStarting_CancelNavigation(object sender, CoreWebView2NavigationStartingEventArgs e)
+        {
+            if (e.Uri.StartsWith("data:")) // when using NavigateToString
+                return;
+
+            var newUri = new Uri(e.Uri);
+            if (newUri == _panel?._currentUri) return;
+            e.Cancel = true;
+
+            // Open in default browser
+            try
+            {
+                if (!Uri.TryCreate(e.Uri, UriKind.Absolute, out var uri))
+                {
+                    Debug.WriteLine($"Invalid URI format: {e.Uri}");
+                    return;
+                }
+
+                // Safe schemes can open directly
+                if (uri.Scheme == Uri.UriSchemeHttp ||
+                    uri.Scheme == Uri.UriSchemeHttps ||
+                    uri.Scheme == Uri.UriSchemeMailto)
+                {
+                    Process.Start(uri.AbsoluteUri);
+                    return;
+                }
+
+                // Ask user for unsafe schemes. Use dispatcher to avoid blocking thread.
+                var associatedApp = GetAssociatedAppForScheme(uri.Scheme);
+                Application.Current.Dispatcher.BeginInvoke(new Action(() =>
+                {
+                    var result = MessageBox.Show(
+                        !string.IsNullOrEmpty(associatedApp) ?
+                        $"The following link will open in {associatedApp}:\n{e.Uri}" : $"The following link will open:\n{e.Uri}",
+                        !string.IsNullOrEmpty(associatedApp) ?
+                        $"Open {associatedApp}?" : "Open custom URI?",
+                        MessageBoxButton.YesNo,
+                        MessageBoxImage.Information);
+
+                    if (result == MessageBoxResult.Yes)
+                    {
+                        Process.Start(e.Uri);
+                    }
+                }));
+            }
+            catch (Exception ex)
+            {
+                Debug.WriteLine($"Failed to open URL in browser: {ex.Message}");
+            }
+        }
+
+        [DllImport("Shlwapi.dll", CharSet = CharSet.Unicode)]
+        private static extern uint AssocQueryString(
+            AssocF flags,
+            AssocStr str,
+            string pszAssoc,
+            string? pszExtra,
+            [Out] StringBuilder? pszOut,
+            ref uint pcchOut);
+
+        [Flags]
+        private enum AssocF
+        {
+            None = 0,
+            VerifyExists = 0x1
+        }
+
+        private enum AssocStr
+        {
+            Command = 1,
+            Executable = 2,
+            FriendlyAppName = 4
+        }
+
+        private string? GetAssociatedAppForScheme(string scheme)
+        {
+            try
+            {
+                // Try to get friendly app name first
+                uint pcchOut = 0;
+                AssocQueryString(AssocF.None, AssocStr.FriendlyAppName, scheme, null, null, ref pcchOut);
+
+                if (pcchOut > 0)
+                {
+                    StringBuilder pszOut = new StringBuilder((int)pcchOut);
+                    AssocQueryString(AssocF.None, AssocStr.FriendlyAppName, scheme, null, pszOut, ref pcchOut);
+
+                    var appName = pszOut.ToString().Trim();
+                    if (!string.IsNullOrEmpty(appName))
+                        return appName;
+                }
+
+                // Fall back to executable name if friendly name is not available
+                pcchOut = 0;
+                AssocQueryString(AssocF.None, AssocStr.Executable, scheme, null, null, ref pcchOut);
+
+                if (pcchOut > 0)
+                {
+                    StringBuilder pszOut = new StringBuilder((int)pcchOut);
+                    AssocQueryString(AssocF.None, AssocStr.Executable, scheme, null, pszOut, ref pcchOut);
+
+                    var exeName = pszOut.ToString().Trim();
+                    if (!string.IsNullOrEmpty(exeName))
+                        return Path.GetFileName(exeName);
+                }
+
+                return null;
+            }
+            catch (Exception ex)
+            {
+                Debug.WriteLine($"Failed to get associated app: {ex.Message}");
+                return null;
+            }
+        }
+
+        private string GenerateMarkdownHtml(string path)
+        {
+            var templatePath = Path.Combine(_resourcePath, "md2html.html");
+
+            if (!File.Exists(templatePath))
+                throw new FileNotFoundException($"Required template file md2html.html not found in extracted resources at {templatePath}");
+
+            var bytes = File.ReadAllBytes(path);
+            var encoding = CharsetDetector.DetectFromBytes(bytes).Detected?.Encoding ?? Encoding.Default;
+            var content = encoding.GetString(bytes);
+
+            var template = File.ReadAllText(templatePath);
+            var html = template.Replace("{{content}}", content);
+
+            // Generate unique filename and ensure it doesn't exist
+            string outputPath;
+            do
+            {
+                var uniqueId = Guid.NewGuid().ToString("N").Substring(0, 8);
+                var outputFileName = $"temp_{uniqueId}.html";
+                outputPath = Path.Combine(_resourcePath, outputFileName);
+            } while (File.Exists(outputPath));
+
+            // Clean up previous file if it exists
+            CleanupTempHtmlFile();
+
+            File.WriteAllText(outputPath, html);
+            _currentHtmlPath = outputPath;
+
+            return outputPath;
+        }
+
+        private void CleanupTempHtmlFile()
+        {
+            if (!string.IsNullOrEmpty(_currentHtmlPath) && File.Exists(_currentHtmlPath))
+            {
+                try
+                {
+                    File.Delete(_currentHtmlPath);
+                }
+                catch (IOException) { } // Ignore deletion errors
+            }
         }
 
         public void Cleanup()
         {
             GC.SuppressFinalize(this);
 
+            CleanupTempHtmlFile();
+
             _panel?.Dispose();
             _panel = null;
         }
-
-        private string GenerateMarkdownHtml(string path)
-        {
-            var bytes = File.ReadAllBytes(path);
-            var encoding = CharsetDetector.DetectFromBytes(bytes).Detected?.Encoding ?? Encoding.Default;
-
-            var md = encoding.GetString(bytes);
-            md = WebUtility.HtmlEncode(md);
-
-            var html = Resources.md2html.Replace("{{content}}", md);
-
-            return html;
-        }
     }
 }

QuickLook.Plugin/QuickLook.Plugin.MarkdownViewer/QuickLook.Plugin.MarkdownViewer.csproj

@@ -70,11 +70,9 @@
     </ItemGroup>
 
     <ItemGroup>
-        <None Remove="Resources\**" />
-    </ItemGroup>
-
-    <ItemGroup>
-        <Resource Include="Resources\**" />
+        <EmbeddedResource Include="Resources\**\*">
+            <LogicalName>QuickLook.Plugin.MarkdownViewer.Resources.%(RecursiveDir)%(Filename)%(Extension)</LogicalName>
+        </EmbeddedResource>
     </ItemGroup>
 
 </Project>

QuickLook.Plugin/QuickLook.Plugin.MarkdownViewer/Resources/highlight.js/styles/github-dark.min.css

@@ -0,0 +1,10 @@
+pre code.hljs{display:block;overflow-x:auto;padding:1em}code.hljs{padding:3px 5px}/*!
+  Theme: GitHub Dark
+  Description: Dark theme as seen on github.com
+  Author: github.com
+  Maintainer: @Hirse
+  Updated: 2021-05-15
+
+  Outdated base version: https://github.com/primer/github-syntax-dark
+  Current colors taken from GitHub's CSS
+*/.hljs{color:#c9d1d9;background:#0d1117}.hljs-doctag,.hljs-keyword,.hljs-meta .hljs-keyword,.hljs-template-tag,.hljs-template-variable,.hljs-type,.hljs-variable.language_{color:#ff7b72}.hljs-title,.hljs-title.class_,.hljs-title.class_.inherited__,.hljs-title.function_{color:#d2a8ff}.hljs-attr,.hljs-attribute,.hljs-literal,.hljs-meta,.hljs-number,.hljs-operator,.hljs-selector-attr,.hljs-selector-class,.hljs-selector-id,.hljs-variable{color:#79c0ff}.hljs-meta .hljs-string,.hljs-regexp,.hljs-string{color:#a5d6ff}.hljs-built_in,.hljs-symbol{color:#ffa657}.hljs-code,.hljs-comment,.hljs-formula{color:#8b949e}.hljs-name,.hljs-quote,.hljs-selector-pseudo,.hljs-selector-tag{color:#7ee787}.hljs-subst{color:#c9d1d9}.hljs-section{color:#1f6feb;font-weight:700}.hljs-bullet{color:#f2cc60}.hljs-emphasis{color:#c9d1d9;font-style:italic}.hljs-strong{color:#c9d1d9;font-weight:700}.hljs-addition{color:#aff5b4;background-color:#033a16}.hljs-deletion{color:#ffdcd7;background-color:#67060c}

QuickLook.Plugin/QuickLook.Plugin.MarkdownViewer/Resources/highlight.js/styles/github.min.css

@@ -0,0 +1,10 @@
+pre code.hljs{display:block;overflow-x:auto;padding:1em}code.hljs{padding:3px 5px}/*!
+  Theme: GitHub
+  Description: Light theme as seen on github.com
+  Author: github.com
+  Maintainer: @Hirse
+  Updated: 2021-05-15
+
+  Outdated base version: https://github.com/primer/github-syntax-light
+  Current colors taken from GitHub's CSS
+*/.hljs{color:#24292e;background:#fff}.hljs-doctag,.hljs-keyword,.hljs-meta .hljs-keyword,.hljs-template-tag,.hljs-template-variable,.hljs-type,.hljs-variable.language_{color:#d73a49}.hljs-title,.hljs-title.class_,.hljs-title.class_.inherited__,.hljs-title.function_{color:#6f42c1}.hljs-attr,.hljs-attribute,.hljs-literal,.hljs-meta,.hljs-number,.hljs-operator,.hljs-selector-attr,.hljs-selector-class,.hljs-selector-id,.hljs-variable{color:#005cc5}.hljs-meta .hljs-string,.hljs-regexp,.hljs-string{color:#032f62}.hljs-built_in,.hljs-symbol{color:#e36209}.hljs-code,.hljs-comment,.hljs-formula{color:#6a737d}.hljs-name,.hljs-quote,.hljs-selector-pseudo,.hljs-selector-tag{color:#22863a}.hljs-subst{color:#24292e}.hljs-section{color:#005cc5;font-weight:700}.hljs-bullet{color:#735c0f}.hljs-emphasis{color:#24292e;font-style:italic}.hljs-strong{color:#24292e;font-weight:700}.hljs-addition{color:#22863a;background-color:#f0fff4}.hljs-deletion{color:#b31d28;background-color:#ffeef0}