[Hosts] Open hosts file in default editor (#21284)

* open hosts file

* open with default editor

src/modules/Hosts/Hosts/Helpers/HostsService.cs

@@ -4,6 +4,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Globalization;
 using System.IO;
 using System.IO.Abstractions;
@@ -14,6 +15,7 @@ using System.Threading;
 using System.Threading.Tasks;
 using Hosts.Models;
 using Hosts.Settings;
+using Microsoft.Win32;
 using Settings.UI.Library.Enumerations;
 
 namespace Hosts.Helpers
@@ -210,6 +212,69 @@ namespace Hosts.Helpers
                 .ForEach(f => f.Delete());
         }
 
+        public void OpenHostsFile()
+        {
+            var notepadFallback = false;
+
+            try
+            {
+                // Try to open in default editor
+                var key = Registry.ClassesRoot.OpenSubKey("SystemFileAssociations\\text\\shell\\edit\\command");
+                if (key != null)
+                {
+                    var commandPattern = key.GetValue(string.Empty).ToString(); // Default value
+                    var file = null as string;
+                    var args = null as string;
+
+                    if (commandPattern.StartsWith('\"'))
+                    {
+                        var endQuoteIndex = commandPattern.IndexOf('\"', 1);
+                        if (endQuoteIndex != -1)
+                        {
+                            file = commandPattern[1..endQuoteIndex];
+                            args = commandPattern[(endQuoteIndex + 1)..].Trim();
+                        }
+                    }
+                    else
+                    {
+                        var spaceIndex = commandPattern.IndexOf(' ');
+                        if (spaceIndex != -1)
+                        {
+                            file = commandPattern[..spaceIndex];
+                            args = commandPattern[(spaceIndex + 1)..].Trim();
+                        }
+                    }
+
+                    if (file != null && args != null)
+                    {
+                        args = args.Replace("%1", HostsFilePath);
+                        Process.Start(new ProcessStartInfo(file, args));
+                    }
+                    else
+                    {
+                        notepadFallback = true;
+                    }
+                }
+            }
+            catch (Exception ex)
+            {
+                Logger.LogError("Failed to open default editor", ex);
+                notepadFallback = true;
+            }
+
+            if (notepadFallback)
+            {
+                try
+                {
+                    Process.Start(new ProcessStartInfo("notepad.exe", HostsFilePath));
+                }
+                catch (Exception ex)
+                {
+                    Logger.LogError("Failed to open notepad", ex);
+                }
+            }
+        }
+
         public void Dispose()
         {
             Dispose(disposing: true);

src/modules/Hosts/Hosts/Helpers/IHostsService.cs

@@ -22,5 +22,7 @@ namespace Hosts.Helpers
         Task<bool> PingAsync(string address);
 
         void CleanupBackup();
+
+        void OpenHostsFile();
     }
 }

src/modules/Hosts/Hosts/Strings/en-us/Resources.resw

@@ -222,6 +222,14 @@
   <data name="MoveUp.Text" xml:space="preserve">
     <value>Move up</value>
   </data>
+  <data name="OpenHostsFileBtn.[using:Microsoft.UI.Xaml.Automation]AutomationProperties.Name" xml:space="preserve">
+    <value>Open hosts file</value>
+    <comment>"Hosts" refers to the system hosts file, do not loc</comment>
+  </data>
+  <data name="OpenHostsFileBtn.[using:Microsoft.UI.Xaml.Controls]ToolTipService.ToolTip" xml:space="preserve">
+    <value>Open hosts file</value>
+    <comment>"Hosts" refers to the system hosts file, do not loc</comment>
+  </data>
   <data name="Ping.Text" xml:space="preserve">
     <value>Ping</value>
     <comment>"Ping" refers to the command-line utility, do not loc</comment>

src/modules/Hosts/Hosts/ViewModels/MainViewModel.cs

@@ -97,6 +97,8 @@ namespace Hosts.ViewModels
 
         public ICommand OpenSettingsCommand => new RelayCommand(OpenSettings);
 
+        public ICommand OpenHostsFileCommand => new RelayCommand(OpenHostsFile);
+
         public MainViewModel(
             IHostsService hostService,
             IUserSettings userSettings)
@@ -197,6 +199,11 @@ namespace Hosts.ViewModels
             SettingsDeepLink.OpenSettings(SettingsDeepLink.SettingsWindow.Hosts);
         }
 
+        public void OpenHostsFile()
+        {
+            _hostsService.OpenHostsFile();
+        }
+
         public void Dispose()
         {
             Dispose(disposing: true);

src/modules/Hosts/Hosts/Views/MainPage.xaml

@@ -125,6 +125,17 @@
                     </Button.Flyout>
                 </Button>
                 
+                <Button
+                    x:Uid="OpenHostsFileBtn"
+                    Height="36"
+                    Command="{x:Bind ViewModel.OpenHostsFileCommand}"
+                    Style="{StaticResource SubtleButtonStyle}">
+                    <FontIcon
+                        FontFamily="{StaticResource SymbolThemeFontFamily}"
+                        FontSize="14"
+                        Glyph="&#xe8a7;" />
+                </Button>
+                
                 <Button
                     x:Uid="SettingsBtn"
                     Height="36"