1 files changed, 35 insertions, 0 deletions
diff --git a/lib/gitlab/asciidoc/mermaid_block_processor.rb b/lib/gitlab/asciidoc/mermaid_block_processor.rb
new file mode 100644
index 00000000000..03d1c7f1961
--- /dev/null
+++ b/lib/gitlab/asciidoc/mermaid_block_processor.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require 'asciidoctor'
+
+module Gitlab
+  module Asciidoc
+    # Mermaid BlockProcessor
+    class MermaidBlockProcessor < ::Asciidoctor::Extensions::BlockProcessor
+      use_dsl
+
+      named :mermaid
+      on_context :literal, :listing
+      parse_content_as :simple
+
+      def process(parent, reader, attrs)
+        create_mermaid_source_block(parent, reader.read, attrs)
+      end
+
+      private
+
+      def create_mermaid_source_block(parent, content, attrs)
+        # If "subs" attribute is specified, substitute accordingly.
+        # Be careful not to specify "specialcharacters" or your diagram code won't be valid anymore!
+        subs = attrs['subs']
+        content = parent.apply_subs(content, parent.resolve_subs(subs)) if subs
+        html = %(<div><pre data-mermaid-style="display">#{CGI.escape_html(content)}</pre></div>)
+        ::Asciidoctor::Block.new(parent, :pass, {
+          content_model: :raw,
+          source: html,
+          subs: :default
+        }.merge(attrs))
+      end
+    end
+  end
+end