69 lines
2.3 KiB
Ruby
69 lines
2.3 KiB
Ruby
# frozen_string_literal: true
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module Banzai
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module Filter
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# HTML Filter for footnotes
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#
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# Footnotes are supported in CommonMark. However we were stripping
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# the ids during sanitization. Those are now allowed.
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#
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# Footnotes are numbered the same - the first one has `id=fn1`, the
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# second is `id=fn2`, etc. In order to allow footnotes when rendering
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# multiple markdown blocks on a page, we need to make each footnote
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# reference unique.
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#
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# This filter adds a random number to each footnote (the same number
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# can be used for a single render). So you get `id=fn1-4335` and `id=fn2-4335`.
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#
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class FootnoteFilter < HTML::Pipeline::Filter
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INTEGER_PATTERN = /\A\d+\z/.freeze
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FOOTNOTE_ID_PREFIX = 'fn'.freeze
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FOOTNOTE_LINK_ID_PREFIX = 'fnref'.freeze
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FOOTNOTE_LI_REFERENCE_PATTERN = /\A#{FOOTNOTE_ID_PREFIX}\d+\z/.freeze
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FOOTNOTE_LINK_REFERENCE_PATTERN = /\A#{FOOTNOTE_LINK_ID_PREFIX}\d+\z/.freeze
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FOOTNOTE_START_NUMBER = 1
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def call
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return doc unless first_footnote = doc.at_css("ol > li[id=#{fn_id(FOOTNOTE_START_NUMBER)}]")
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# Sanitization stripped off the section wrapper - add it back in
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first_footnote.parent.wrap('<section class="footnotes">')
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rand_suffix = "-#{random_number}"
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doc.css('sup > a[id]').each do |link_node|
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ref_num = link_node[:id].delete_prefix(FOOTNOTE_LINK_ID_PREFIX)
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footnote_node = doc.at_css("li[id=#{fn_id(ref_num)}]")
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backref_node = footnote_node.at_css("a[href=\"##{fnref_id(ref_num)}\"]")
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if ref_num =~ INTEGER_PATTERN && footnote_node && backref_node
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link_node[:href] += rand_suffix
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link_node[:id] += rand_suffix
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footnote_node[:id] += rand_suffix
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backref_node[:href] += rand_suffix
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# Sanitization stripped off class - add it back in
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link_node.parent.append_class('footnote-ref')
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backref_node.append_class('footnote-backref')
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end
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end
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doc
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end
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private
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def random_number
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@random_number ||= rand(10000)
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end
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def fn_id(num)
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"#{FOOTNOTE_ID_PREFIX}#{num}"
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end
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def fnref_id(num)
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"#{FOOTNOTE_LINK_ID_PREFIX}#{num}"
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end
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end
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end
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end
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