[Peek] Add support for previewing AutoHotKey files, CSV, and other plaintext files

src/common/FilePreviewCommon/Assets/Monaco/monacoExtraExtensions.txt

@@ -0,0 +1,5 @@
+# Extra file extensions to preview with Monaco.
+
+.ahk	# AutoHotKey scripts
+.csv	# comma-separated values
+.tsv	# tab-separated values

src/common/FilePreviewCommon/FilePreviewCommon.csproj

@@ -26,6 +26,9 @@
     <None Update="Assets\Monaco\index.html">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>
+    <None Update="Assets\Monaco\monacoExtraExtensions.txt">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
     <None Update="Assets\Monaco\monacoSpecialLanguages.js">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>

src/modules/peek/Peek.FilePreviewer/Previewers/ShellPreviewHandlerPreviewer/ShellPreviewHandlerPreviewer.cs

@@ -206,9 +206,14 @@ public void Clear()
             }
         }
 
+        public static bool IsExtensionSupported(string extension)
+        {
+            return !string.IsNullOrEmpty(GetPreviewHandlerGuid(extension));
+        }
+
         public static bool IsItemSupported(IFileSystemItem item)
         {
-            return !string.IsNullOrEmpty(GetPreviewHandlerGuid(item.Extension));
+            return IsExtensionSupported(item.Extension);
         }
 
         private static string? GetPreviewHandlerGuid(string fileExt)

src/modules/peek/Peek.FilePreviewer/Previewers/WebBrowserPreviewer/Helpers/MonacoHelper.cs

@@ -8,21 +8,28 @@
 using System.IO;
 using System.Linq;
 using System.Text.Json;
+using System.Text.RegularExpressions;
 using Common.UI;
 using ManagedCommon;
 
 namespace Peek.FilePreviewer.Previewers
 {
-    public class MonacoHelper
+    public partial class MonacoHelper
     {
-        public static readonly HashSet<string> SupportedMonacoFileTypes = GetExtensions();
+        public static readonly HashSet<string> SupportedMonacoFileTypes;
+
+        static MonacoHelper()
+        {
+            SupportedMonacoFileTypes = GetExtensions().Union(GetExtraSupportedExtensions()).ToHashSet();
+        }
 
         public static HashSet<string> GetExtensions()
         {
-            HashSet<string> set = new HashSet<string>();
+            HashSet<string> set = [];
+
             try
             {
-                JsonDocument languageListDocument = Microsoft.PowerToys.FilePreviewCommon.MonacoHelper.GetLanguages();
+                using JsonDocument languageListDocument = Microsoft.PowerToys.FilePreviewCommon.MonacoHelper.GetLanguages();
                 JsonElement languageList = languageListDocument.RootElement.GetProperty("list");
                 foreach (JsonElement e in languageList.EnumerateArray())
                 {
@@ -43,6 +50,39 @@ public static HashSet<string> GetExtensions()
             return set;
         }
 
+        /// <summary>
+        /// Get the file extensions which are not present in the JSON languages document but which
+        /// may still be previewed by Monaco.
+        /// </summary>
+        /// <remarks>Filters out extensions handled by Shell preview handlers, so Office will still
+        /// handle rendering .csv and others if it is installed.</remarks>
+        private static IEnumerable<string> GetExtraSupportedExtensions()
+        {
+            try
+            {
+                string path = Path.Combine(
+                    Microsoft.PowerToys.FilePreviewCommon.MonacoHelper.GetRuntimeMonacoDirectory(),
+                    "monacoExtraExtensions.txt");
+
+                return File.Exists(path) ?
+                    File.ReadAllLines(path)
+                        .Select(line => ExtensionsFileRegex().Match(line))
+                        .Where(match => match.Success &&
+                            !ShellPreviewHandlerPreviewer.IsExtensionSupported(match.Groups[1].Value))
+                        .Select(match => match.Groups[1].Value) : [];
+            }
+            catch
+            {
+                return [];
+            }
+        }
+
+        /// <summary>
+        /// Extracts the extensions from the extra supported extensions file, ignoring comments.
+        /// </summary>
+        [GeneratedRegex(@"^\s*(\.\w+)\s*(#.*)?$")]
+        private static partial Regex ExtensionsFileRegex();
+
         /// <summary>
         /// Prepares temp html for the previewing
         /// </summary>