Add Mermaid support and .mmd detection #1893

QuickLook.Plugin/QuickLook.Plugin.MarkdownViewer/MarkdownPanel.cs

@@ -78,6 +78,7 @@ public class MarkdownPanel : WebpagePanel
         var bytes = File.ReadAllBytes(path);
         var encoding = CharsetDetector.DetectFromBytes(bytes).Detected?.Encoding ?? Encoding.Default;
         var content = encoding.GetString(bytes);
+        content = PrepareMarkdownContent(path, content);
 
         var template = ReadString("/md2html.html");
         
@@ -99,6 +100,75 @@ public class MarkdownPanel : WebpagePanel
         return html;
     }
 
+    private static string PrepareMarkdownContent(string path, string content)
+    {
+        var extension = Path.GetExtension(path);
+
+        if (extension.Equals(".mermaid", StringComparison.OrdinalIgnoreCase))
+            return WrapAsMermaidCodeFence(content);
+
+        if (extension.Equals(".mmd", StringComparison.OrdinalIgnoreCase)
+            && IsLikelyMermaidDocument(content))
+            return WrapAsMermaidCodeFence(content);
+
+        return content;
+    }
+
+    private static string WrapAsMermaidCodeFence(string content)
+    {
+        var normalized = content.Replace("\r\n", "\n").Trim('\n');
+        return $"```mermaid\n{normalized}\n```";
+    }
+
+    private static bool IsLikelyMermaidDocument(string content)
+    {
+        if (string.IsNullOrWhiteSpace(content))
+            return false;
+
+        if (content.IndexOf("```mermaid", StringComparison.OrdinalIgnoreCase) >= 0)
+            return false;
+
+        using var reader = new StringReader(content);
+        string line;
+        while ((line = reader.ReadLine()) != null)
+        {
+            var trimmed = line.Trim();
+            if (trimmed.Length == 0 || trimmed.StartsWith("%%", StringComparison.Ordinal))
+                continue;
+
+            return trimmed.StartsWith("graph ", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.Equals("graph", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("flowchart ", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.Equals("flowchart", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("sequenceDiagram", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("classDiagram", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("stateDiagram", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("stateDiagram-v2", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("erDiagram", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("journey", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("gantt", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("pie", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("mindmap", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("timeline", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("gitGraph", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("quadrantChart", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("requirementDiagram", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("c4Context", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("c4Container", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("c4Component", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("c4Dynamic", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("c4Deployment", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("xychart-beta", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("block-beta", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("packet-beta", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("architecture-beta", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("kanban", StringComparison.OrdinalIgnoreCase)
+                   || trimmed.StartsWith("sankey-beta", StringComparison.OrdinalIgnoreCase);
+        }
+
+        return false;
+    }
+
     protected override void WebView_WebResourceRequested(object sender, CoreWebView2WebResourceRequestedEventArgs args)
     {
         Debug.WriteLine($"[{args.Request.Method}] {args.Request.Uri}");

QuickLook.Plugin/QuickLook.Plugin.MarkdownViewer/Plugin.cs

@@ -35,7 +35,8 @@ public sealed class Plugin : IViewer
     [
         ".md", ".markdown", // The most common Markdown extensions
         ".mdx", // MDX (Markdown + JSX), used in React ecosystems
-        ".mmd", // MultiMarkdown (MMD), an extended version of Markdown
+        ".mmd", // MultiMarkdown (MMD), an extended version of Markdown or Mermaid diagram source file
+        ".mermaid", // Mermaid diagram source file
         ".mkd", ".mdwn", ".mdown", // Early Markdown variants, used by different parsers like Pandoc, Gitit, and Hakyll
         ".mdc", // A Markdown variant used by Cursor AI [Repeated format from ImageViewer]
         ".qmd", // Quarto Markdown, developed by RStudio for scientific computing and reproducible reports