1 files changed, 62 insertions, 0 deletions
diff --git a/_plugins/toc.rb b/_plugins/toc.rb
new file mode 100644
index 0000000..216341d
--- /dev/null
+++ b/_plugins/toc.rb
@@ -0,0 +1,62 @@
+require 'nokogiri'
+
+module Jekyll
+  class TOC < Liquid::Tag
+    def render context
+      # load HTML into nokogiri
+      html = context.registers[:page]['content']
+      doc = Nokogiri::HTML(html)
+
+      # enumerate over all h1-4 headings
+      @els = doc.css("h1, h2, h3, h4")
+      return '<div class="chapterChildren">%s</div>' % [ output_toc ]
+    end
+
+    def output_toc
+      # empty toc (this check prevents crash)
+      return "" if @els.length == 0
+
+      output = '<ul>'
+
+      current_level = el_level(@els[0])
+
+      while @els.length > 0
+        el = @els[0]
+        el_next = @els[1]
+        level = el_level(el)
+        level_next = el_level(el_next || el) # || el to prevent crash on end of list
+
+        if level >= level_next
+          output += '<li>'
+        else
+          output += '<li class="stub"><details open>'
+          output += '<summary>'
+        end
+
+        output += '<a href="#%s">%s</a>' % [ el['id'], el.inner_html ]
+        @els.shift()
+
+        if level >= level_next
+          output += '</li>'
+        else
+          output += '</summary>'
+          output += output_toc
+          output += '</details></li>'
+        end
+
+        break if level_next < level
+      end
+
+      output += '</ul>'
+
+      return output
+    end
+
+    def el_level el
+      return Integer(el.name[1..])
+    end
+  end
+end
+
+Liquid::Template.register_tag('toc', Jekyll::TOC)
+