Initial commit

Assisted-by: GLM 5.3

internal/markdown/diagram.go

@@ -0,0 +1,34 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: PolyForm-Noncommercial-1.0.0
+
+package markdown
+
+import (
+	stdhtml "html"
+	"regexp"
+
+	"sourcedock.dev/petrbalvin/scriptorium"
+)
+
+// mermaidBlockRe matches the fenced mermaid blocks the renderer writes.
+// The diagram source arrives HTML-escaped, as code content always does.
+var mermaidBlockRe = regexp.MustCompile(`(?s)<pre><code class="language-mermaid">(.*?)</code></pre>`)
+
+// renderDiagrams replaces every fenced mermaid block with the SVG
+// scriptorium draws from it, wrapped so a style sheet can tell diagrams
+// from prose. It runs on sanitised HTML: the SVG is machine-drawn output
+// whose vocabulary the library itself bounds, and the sanitiser's
+// HTML-only parser would corrupt its case-sensitive attributes. A
+// diagram the library does not carry, or a line it cannot parse, keeps
+// its code block: the author sees the source that was not understood,
+// and the reader never a half-drawn figure.
+func renderDiagrams(html string) string {
+	return mermaidBlockRe.ReplaceAllStringFunc(html, func(block string) string {
+		src := stdhtml.UnescapeString(mermaidBlockRe.FindStringSubmatch(block)[1])
+		svg, err := scriptorium.RenderDiagram([]byte(src))
+		if err != nil {
+			return block
+		}
+		return `<div class="diagram">` + "\n" + string(svg) + "\n</div>"
+	})
+}