Class: Banzai::Filter::FootnoteFilter

Inherits:
HTML::Pipeline::Filter
  • Object
show all
Defined in:
lib/banzai/filter/footnote_filter.rb

Overview

HTML Filter for footnotes

Footnotes are supported in CommonMark. However we were stripping the ids during sanitization. Those are now allowed.

Footnotes are numbered the same - the first one has `id=fn1`, the second is `id=fn2`, etc. In order to allow footnotes when rendering multiple markdown blocks on a page, we need to make each footnote reference unique.

This filter adds a random number to each footnote (the same number can be used for a single render). So you get `id=fn1-4335` and `id=fn2-4335`.

Constant Summary collapse

INTEGER_PATTERN =
/\A\d+\z/.freeze
FOOTNOTE_ID_PREFIX =
'fn'
'fnref'
FOOTNOTE_LI_REFERENCE_PATTERN =
/\A#{FOOTNOTE_ID_PREFIX}\d+\z/.freeze
/\A#{FOOTNOTE_LINK_ID_PREFIX}\d+\z/.freeze
FOOTNOTE_START_NUMBER =
1

Instance Method Summary collapse

Instance Method Details

#callObject


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# File 'lib/banzai/filter/footnote_filter.rb', line 26

def call
  return doc unless first_footnote = doc.at_css("ol > li[id=#{fn_id(FOOTNOTE_START_NUMBER)}]")

  # Sanitization stripped off the section wrapper - add it back in
  first_footnote.parent.wrap('<section class="footnotes">')
  rand_suffix = "-#{random_number}"
  modified_footnotes = {}

  doc.css('sup > a[id]').each do |link_node|
    ref_num       = link_node[:id].delete_prefix(FOOTNOTE_LINK_ID_PREFIX)
    footnote_node = doc.at_css("li[id=#{fn_id(ref_num)}]")

    if INTEGER_PATTERN.match?(ref_num) && (footnote_node || modified_footnotes[ref_num])
      link_node[:href] += rand_suffix
      link_node[:id]   += rand_suffix

      # Sanitization stripped off class - add it back in
      link_node.parent.append_class('footnote-ref')

      unless modified_footnotes[ref_num]
        footnote_node[:id] += rand_suffix
        backref_node        = footnote_node.at_css("a[href=\"##{fnref_id(ref_num)}\"]")

        if backref_node
          backref_node[:href] += rand_suffix
          backref_node.append_class('footnote-backref')
        end

        modified_footnotes[ref_num] = true
      end
    end
  end

  doc
end