Add bootstrap alert renderer

src/Markdig/Extensions/Bootstrap/BootstrapAlertRenderer.cs

@@ -0,0 +1,72 @@
+// Copyright (c) Alexandre Mutel. All rights reserved.
+// This file is licensed under the BSD-Clause 2 license.
+// See the license.txt file in the project root for more information.
+
+using System.Linq;
+using Markdig.Extensions.Alerts;
+using Markdig.Renderers;
+using Markdig.Renderers.Html;
+using Markdig.Syntax;
+
+namespace Markdig.Extensions.Bootstrap;
+
+/// <summary>
+/// A HTML renderer for a <see cref="AlertBlock"/> that adds bootstrap classes.
+/// </summary>
+/// <seealso cref="HtmlObjectRenderer{AlertBlock}" />
+public class BootstrapAlertRenderer : HtmlObjectRenderer<AlertBlock>
+{
+    /// <summary>
+    /// Creates a new instance of this renderer.
+    /// </summary>
+    public BootstrapAlertRenderer() { }
+
+    /// <inheritdoc />
+    protected override void Write(HtmlRenderer renderer, AlertBlock obj)
+    {
+        AddAttributes(obj);
+        var lastParagraph = obj.Descendants().OfType<ParagraphBlock>().LastOrDefault();
+        lastParagraph?.GetAttributes().AddProperty("style", "margin-bottom: 0");
+
+        renderer.EnsureLine();
+        if (renderer.EnableHtmlForBlock)
+        {
+            renderer.Write("<div");
+            renderer.WriteAttributes(obj);
+            renderer.WriteLine('>');
+        }
+
+        var savedImplicitParagraph = renderer.ImplicitParagraph;
+        renderer.ImplicitParagraph = false;
+        renderer.WriteChildren(obj);
+        renderer.ImplicitParagraph = savedImplicitParagraph;
+        if (renderer.EnableHtmlForBlock)
+        {
+            renderer.WriteLine("</div>");
+        }
+
+        renderer.EnsureLine();
+    }
+
+    private static void AddAttributes(AlertBlock obj)
+    {
+        var attributes = obj.GetAttributes();
+        attributes.AddClass("alert");
+        attributes.AddProperty("role", "alert");
+
+        string? @class = obj.Kind.AsSpan() switch
+        {
+            "NOTE" => "alert-primary",
+            "TIP" => "alert-success",
+            "IMPORTANT" => "alert-info",
+            "WARNING" => "alert-warning",
+            "CAUTION" => "alert-danger",
+            _ => null
+        };
+
+        if (@class is not null)
+        {
+            attributes.AddClass(@class);
+        }
+    }
+}

src/Markdig/Extensions/Bootstrap/BootstrapExtension.cs

@@ -1,7 +1,8 @@
 // Copyright (c) Alexandre Mutel. All rights reserved.
-// This file is licensed under the BSD-Clause 2 license. 
+// This file is licensed under the BSD-Clause 2 license.
 // See the license.txt file in the project root for more information.
 
+using Markdig.Extensions.Alerts;
 using Markdig.Renderers;
 using Markdig.Renderers.Html;
 using Markdig.Syntax;
@@ -24,6 +25,15 @@ public void Setup(MarkdownPipelineBuilder pipeline)
 
     public void Setup(MarkdownPipeline pipeline, IMarkdownRenderer renderer)
     {
+        if (renderer is HtmlRenderer htmlRenderer)
+        {
+            // We only want to add our renderer if we already support alert blocks
+            if (htmlRenderer.ObjectRenderers.Contains<AlertBlockRenderer>())
+            {
+                // Needs to be inserted before the original renderer
+                htmlRenderer.ObjectRenderers.Insert(0, new BootstrapAlertRenderer());
+            }
+        }
     }
 
     private static void PipelineOnDocumentProcessed(MarkdownDocument document)
@@ -43,7 +53,7 @@ private static void PipelineOnDocumentProcessed(MarkdownDocument document)
                 {
                     node.GetAttributes().AddClass("table");
                 }
-                else if (node is QuoteBlock)
+                else if (node is QuoteBlock and not AlertBlock)
                 {
                     node.GetAttributes().AddClass("blockquote");
                 }