1 files changed, 63 insertions, 0 deletions
diff --git a/lib/banzai/filter/table_of_contents_filter.rb b/lib/banzai/filter/table_of_contents_filter.rb
new file mode 100644
index 00000000000..92d130074dc
--- /dev/null
+++ b/lib/banzai/filter/table_of_contents_filter.rb
@@ -0,0 +1,63 @@
+require 'banzai'
+require 'html/pipeline/filter'
+
+module Banzai
+  module Filter
+    # HTML filter that adds an anchor child element to all Headers in a
+    # document, so that they can be linked to.
+    #
+    # Generates the Table of Contents with links to each header. See Results.
+    #
+    # Based on HTML::Pipeline::TableOfContentsFilter.
+    #
+    # Context options:
+    #   :no_header_anchors - Skips all processing done by this filter.
+    #
+    # Results:
+    #   :toc - String containing Table of Contents data as a `ul` element with
+    #          `li` child elements.
+    class TableOfContentsFilter < HTML::Pipeline::Filter
+      PUNCTUATION_REGEXP = /[^\p{Word}\- ]/u
+
+      def call
+        return doc if context[:no_header_anchors]
+
+        result[:toc] = ""
+
+        headers = Hash.new(0)
+
+        doc.css('h1, h2, h3, h4, h5, h6').each do |node|
+          text = node.text
+
+          id = text.downcase
+          id.gsub!(PUNCTUATION_REGEXP, '') # remove punctuation
+          id.gsub!(' ', '-') # replace spaces with dash
+          id.squeeze!('-') # replace multiple dashes with one
+
+          uniq = (headers[id] > 0) ? "-#{headers[id]}" : ''
+          headers[id] += 1
+
+          if header_content = node.children.first
+            href = "#{id}#{uniq}"
+            push_toc(href, text)
+            header_content.add_previous_sibling(anchor_tag(href))
+          end
+        end
+
+        result[:toc] = %Q{<ul class="section-nav">\n#{result[:toc]}</ul>} unless result[:toc].empty?
+
+        doc
+      end
+
+      private
+
+      def anchor_tag(href)
+        %Q{<a id="#{href}" class="anchor" href="##{href}" aria-hidden="true"></a>}
+      end
+
+      def push_toc(href, text)
+        result[:toc] << %Q{<li><a href="##{href}">#{text}</a></li>\n}
+      end
+    end
+  end
+end