2 files changed, 23 insertions, 0 deletions
diff --git a/Rules b/Rules
index 867a7cca..77998113 100644
--- a/Rules
+++ b/Rules
@@ -82,6 +82,8 @@ compile '/**/*.md' do
       toc_levels: 2..5,
       with_toc: include_toc
 
+    filter :convert_mermaid_html
+
     filter :colorize_syntax,
       default_colorizer: :rouge
 
diff --git a/lib/filters/convert_mermaid_html.rb b/lib/filters/convert_mermaid_html.rb
new file mode 100644
index 00000000..770502b1
--- /dev/null
+++ b/lib/filters/convert_mermaid_html.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+class ConvertMermaidHtml < Nanoc::Filter
+  identifier :convert_mermaid_html
+
+  MERMAID_HTML_PATTERN = %r{<div\ class="mermaid">(?<mermaid_content>.*?)</div>}mx
+
+  def run(content, params = {})
+    content.gsub(MERMAID_HTML_PATTERN) { generate(Regexp.last_match[:mermaid_content]) }
+  end
+
+  def generate(content)
+    fixed_content = content
+      .gsub('&', '&amp;')
+      .gsub('<', '&lt;')
+      .gsub('>', '&gt;')
+      .gsub('"', '&quot;')
+
+    %(<div class="mermaid">#{fixed_content}</div>)
+  end
+end