Highlighted code blocks inside the app (#1153)

app/MindWork AI Studio/Components/HighlightedMarkdown.cs

@@ -0,0 +1,55 @@
+using AIStudio.Tools.CodeHighlighting;
+
+using Microsoft.AspNetCore.Components.Rendering;
+
+namespace AIStudio.Components;
+
+/// <summary>
+/// Renders Markdown the way MudMarkdown does, and highlights the code blocks of more languages than
+/// the library does, such as Python or SQL.
+/// </summary>
+/// <remarks>
+/// MudBlazor.Markdown highlights only a few languages itself, and its highlighter is internal.
+/// MudMarkdown renders every code block through RenderCodeBlock, though, and lets us override that.
+/// A block in one of the languages of CodeHighlighters becomes a HighlightedCodeBlock; any other block
+/// stays as the library renders it. A block which names no language gets the one its code is written in,
+/// see CodeLanguageDetector, the same as when it is saved as a file.
+/// </remarks>
+public class HighlightedMarkdown : MudMarkdown
+{
+    /// <summary>
+    /// The text of a code block: its lines, each with the line break it came with.
+    /// </summary>
+    /// <param name="code">The code block, as Markdig read it.</param>
+    /// <returns>The text of the block.</returns>
+    internal static string TextOf(Markdig.Syntax.CodeBlock code) => code.Lines.ToString();
+
+    #region Overrides of MudMarkdown
+
+    /// <inheritdoc />
+    protected override void RenderCodeBlock(in RenderTreeBuilder builder, ref int elementIndex, in Markdig.Syntax.CodeBlock code, in string? info)
+    {
+        var text = TextOf(code);
+        var language = CodeLanguageDetector.FenceLanguageOf(info, text);
+        if (!CodeHighlighters.TryGetRules(language, out _))
+        {
+            //
+            // The copy button of the library confirms in the language of the app, as ours does:
+            //
+            this.Styling.CodeBlock.CopyButtonText = CodeBlockCopyButton.ConfirmationText;
+            base.RenderCodeBlock(builder, ref elementIndex, code, language);
+            return;
+        }
+
+        //
+        // Our frames are numbered by their place in this method, as Blazor asks for. The frames of
+        // the library keep the running count it hands through every render method instead:
+        //
+        builder.OpenComponent<HighlightedCodeBlock>(0);
+        builder.AddComponentParameter(1, nameof(HighlightedCodeBlock.Code), text);
+        builder.AddComponentParameter(2, nameof(HighlightedCodeBlock.Language), language);
+        builder.CloseComponent();
+    }
+
+    #endregion
+}