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# frozen_string_literal: true
module Banzai
module Filter
# 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`.
#
class FootnoteFilter < HTML::Pipeline::Filter
INTEGER_PATTERN = /\A\d+\z/.freeze
FOOTNOTE_ID_PREFIX = 'fn'.freeze
FOOTNOTE_LINK_ID_PREFIX = 'fnref'.freeze
FOOTNOTE_LI_REFERENCE_PATTERN = /\A#{FOOTNOTE_ID_PREFIX}\d+\z/.freeze
FOOTNOTE_LINK_REFERENCE_PATTERN = /\A#{FOOTNOTE_LINK_ID_PREFIX}\d+\z/.freeze
FOOTNOTE_START_NUMBER = 1
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
private
def random_number
@random_number ||= rand(10000)
end
def fn_id(num)
"#{FOOTNOTE_ID_PREFIX}#{num}"
end
def fnref_id(num)
"#{FOOTNOTE_LINK_ID_PREFIX}#{num}"
end
end
end
end
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