feat: Add plugin system for changelog viewers

Implements a flexible plugin system for displaying changelog content with multiple viewer options:
- Add IChangelogViewer interface for viewer implementations
- Add RichTextBox viewer for simple text display
- Add WebBrowser viewer for legacy IE-based browser
- Add WebView2 viewer for modern Edge WebView2
- Add ChangelogViewerFactory for viewer instantiation

Users can now:
- Choose their preferred viewer type via AutoUpdater.ChangelogViewerType
- Load content directly as text or from URL (where supported)
- Extend the system with custom viewer implementations

The system automatically handles viewer initialization, cleanup, and fallback behavior when preferred viewers are unavailable.

Author: w4po

AutoUpdater.NET/AutoUpdater.cs

@@ -0,0 +1,26 @@
+using System;
+
+namespace AutoUpdaterDotNET.ChangelogViewers;
+
+public static class ChangelogViewerFactory
+{
+    public static IChangelogViewer Create(ChangelogViewerType type)
+    {
+        return type switch
+        {
+            ChangelogViewerType.RichTextBox => new RichTextBoxViewer(),
+            ChangelogViewerType.WebBrowser => new WebBrowserViewer(),
+            ChangelogViewerType.WebView2 when WebView2Viewer.IsAvailable() => new WebView2Viewer(),
+            ChangelogViewerType.WebView2 => throw new InvalidOperationException("WebView2 runtime is not available"),
+            _ => throw new ArgumentException($"Unknown viewer type: {type}")
+        };
+    }
+
+    public static ChangelogViewerType GetDefaultViewerType()
+    {
+        if (WebView2Viewer.IsAvailable())
+            return ChangelogViewerType.WebView2;
+            
+        return ChangelogViewerType.WebBrowser;
+    }
+}

AutoUpdater.NET/ChangelogViewers/ChangelogViewerFactory.cs

@@ -0,0 +1,8 @@
+namespace AutoUpdaterDotNET.ChangelogViewers;
+
+public enum ChangelogViewerType
+{
+    RichTextBox,
+    WebBrowser,
+    WebView2
+}

AutoUpdater.NET/ChangelogViewers/ChangelogViewerType.cs

@@ -0,0 +1,12 @@
+using System.Windows.Forms;
+
+namespace AutoUpdaterDotNET.ChangelogViewers;
+
+public interface IChangelogViewer
+{
+    Control Control { get; }
+    bool SupportsUrl { get; }
+    void LoadContent(string content);
+    void LoadUrl(string url);
+    void Cleanup();
+}

AutoUpdater.NET/ChangelogViewers/IChangelogViewer.cs

@@ -0,0 +1,31 @@
+using System.Windows.Forms;
+
+namespace AutoUpdaterDotNET.ChangelogViewers;
+
+public class RichTextBoxViewer : IChangelogViewer
+{
+    private readonly RichTextBox _richTextBox = new()
+    {
+        ReadOnly = true,
+        Dock = DockStyle.Fill,
+        BackColor = System.Drawing.SystemColors.Control,
+        BorderStyle = BorderStyle.Fixed3D
+    };
+    public Control Control => _richTextBox;
+    public bool SupportsUrl => false;
+
+    public void LoadContent(string content)
+    {
+        _richTextBox.Text = content;
+    }
+
+    public void LoadUrl(string url)
+    {
+        throw new System.NotSupportedException("RichTextBox does not support loading from URL");
+    }
+
+    public void Cleanup()
+    {
+        _richTextBox.Dispose();
+    }
+}

AutoUpdater.NET/ChangelogViewers/RichTextBoxViewer.cs

@@ -0,0 +1,91 @@
+using System.IO;
+using System.Diagnostics;
+using System.Windows.Forms;
+using Microsoft.Win32;
+
+namespace AutoUpdaterDotNET.ChangelogViewers;
+
+public class WebBrowserViewer : IChangelogViewer
+{
+    private const string EmulationKey = @"SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_BROWSER_EMULATION";
+    private readonly int _emulationValue;
+    private readonly string _executableName;
+    private readonly WebBrowser _webBrowser;
+    public Control Control => _webBrowser;
+    public bool SupportsUrl => true;
+
+    public WebBrowserViewer()
+    {
+        _webBrowser = new WebBrowser
+        {
+            Dock = DockStyle.Fill,
+            ScriptErrorsSuppressed = true,
+            AllowWebBrowserDrop = false,
+            WebBrowserShortcutsEnabled = false,
+            IsWebBrowserContextMenuEnabled = false
+        };
+
+        _executableName = Path.GetFileName(
+            Process.GetCurrentProcess().MainModule?.FileName
+            ?? System.Reflection.Assembly.GetEntryAssembly()?.Location
+            ?? Application.ExecutablePath);
+
+        _emulationValue = _webBrowser.Version.Major switch
+        {
+            11 => 11001,
+            10 => 10001,
+            9 => 9999,
+            8 => 8888,
+            7 => 7000,
+            _ => 0
+        };
+
+        SetupEmulation();
+    }
+
+    public void LoadContent(string content) => _webBrowser.DocumentText = content;
+
+    public void LoadUrl(string url)
+    {
+        if (AutoUpdater.BasicAuthChangeLog != null)
+            _webBrowser.Navigate(url, "", null, $"Authorization: {AutoUpdater.BasicAuthChangeLog}");
+        else
+            _webBrowser.Navigate(url);
+    }
+    private void SetupEmulation()
+    {
+        if (_emulationValue == 0)
+            return;
+
+        try
+        {
+            using var registryKey = Registry.CurrentUser.OpenSubKey(EmulationKey, true);
+            registryKey?.SetValue(_executableName, _emulationValue, RegistryValueKind.DWord);
+        }
+        catch
+        {
+            // ignored
+        }
+    }
+    private void RemoveEmulation()
+    {
+        if (_emulationValue == 0)
+            return;
+
+        try
+        {
+            using var registryKey = Registry.CurrentUser.OpenSubKey(EmulationKey, true);
+            registryKey?.DeleteValue(_executableName, false);
+        }
+        catch
+        {
+            // ignored
+        }
+    }
+
+    public void Cleanup()
+    {
+        _webBrowser.Dispose();
+        RemoveEmulation();
+    }
+}

AutoUpdater.NET/ChangelogViewers/WebBrowserViewer.cs

@@ -0,0 +1,96 @@
+using System;
+using System.IO;
+using System.Windows.Forms;
+using System.Threading.Tasks;
+using Microsoft.Web.WebView2.Core;
+using Microsoft.Web.WebView2.WinForms;
+
+namespace AutoUpdaterDotNET.ChangelogViewers;
+
+public class WebView2Viewer : IChangelogViewer
+{
+    private bool _isInitialized;
+    private readonly WebView2 _webView = new()
+    {
+        Dock = DockStyle.Fill,
+        AllowExternalDrop = false
+    };
+    public Control Control => _webView;
+    public bool SupportsUrl => true;
+
+    private async Task EnsureInitialized()
+    {
+        if (_isInitialized) return;
+
+        try
+        {
+            await _webView.EnsureCoreWebView2Async(await CoreWebView2Environment.CreateAsync(null, Path.GetTempPath()));
+            _isInitialized = true;
+        }
+        catch (Exception)
+        {
+            throw new InvalidOperationException("WebView2 runtime is not available");
+        }
+    }
+
+    public async void LoadContent(string content)
+    {
+        await EnsureInitialized();
+        _webView.CoreWebView2.SetVirtualHostNameToFolderMapping("local.files", Path.GetTempPath(), CoreWebView2HostResourceAccessKind.Allow);
+            
+        // Write content to a temporary HTML file
+        var tempFile = Path.Combine(Path.GetTempPath(), "changelog.html");
+        File.WriteAllText(tempFile, content);
+            
+        // Navigate to the local file
+        _webView.CoreWebView2.Navigate("https://local.files/changelog.html");
+    }
+
+    public async void LoadUrl(string url)
+    {
+        await EnsureInitialized();
+
+        if (AutoUpdater.BasicAuthChangeLog != null)
+        {
+            _webView.CoreWebView2.BasicAuthenticationRequested += delegate (object _, CoreWebView2BasicAuthenticationRequestedEventArgs args)
+            {
+                args.Response.UserName = ((BasicAuthentication)AutoUpdater.BasicAuthChangeLog).Username;
+                args.Response.Password = ((BasicAuthentication)AutoUpdater.BasicAuthChangeLog).Password;
+            };
+        }
+
+        _webView.CoreWebView2.Navigate(url);
+    }
+
+    public void Cleanup()
+    {
+        if (File.Exists(Path.Combine(Path.GetTempPath(), "changelog.html")))
+        {
+            try
+            {
+                File.Delete(Path.Combine(Path.GetTempPath(), "changelog.html"));
+            }
+            catch
+            {
+                // Ignore deletion errors
+            }
+        }
+        _webView.Dispose();
+    }
+
+    public static bool IsAvailable()
+    {
+        try
+        {
+            var availableBrowserVersion = CoreWebView2Environment.GetAvailableBrowserVersionString(null);
+            const string requiredMinBrowserVersion = "86.0.616.0";
+            return !string.IsNullOrEmpty(availableBrowserVersion) &&
+                   CoreWebView2Environment.CompareBrowserVersions(availableBrowserVersion,
+                       requiredMinBrowserVersion) >= 0;
+        }
+        catch (Exception)
+        {
+            return false;
+        }
+    }
+}