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# frozen_string_literal: true
# Generated HTML is transformed back to GFM by:
# - app/assets/javascripts/behaviors/markdown/marks/math.js
# - app/assets/javascripts/behaviors/markdown/nodes/code_block.js
module Banzai
module Filter
# HTML filter that implements our dollar math syntax, one of three filters:
# DollarMathPreFilter, DollarMathPostFilter, and MathFilter
#
class DollarMathPostFilter < HTML::Pipeline::Filter
# Based on the Pandoc heuristics,
# https://pandoc.org/MANUAL.html#extension-tex_math_dollars
#
# Handle the $...$ and $$...$$ inline syntax in this filter, after markdown processing
# but before post-handling of escaped characters. Any escaped $ will have been specially
# encoded and will therefore not interfere with the detection of the dollar syntax.
# Corresponds to the "$...$" syntax
DOLLAR_INLINE_PATTERN = %r{
(?<matched>\$(?<math>(?:\S[^$\n]*?\S|[^$\s]))\$)(?:[^\d]|$)
}x.freeze
# Corresponds to the "$$...$$" syntax
DOLLAR_DISPLAY_INLINE_PATTERN = %r{
(?<matched>\$\$\ *(?<math>[^$\n]+?)\ *\$\$)
}x.freeze
# Order dependent. Handle the `$$` syntax before the `$` syntax
DOLLAR_MATH_PIPELINE = [
{ pattern: DOLLAR_DISPLAY_INLINE_PATTERN, style: :display },
{ pattern: DOLLAR_INLINE_PATTERN, style: :inline }
].freeze
# Do not recognize math inside these tags
IGNORED_ANCESTOR_TAGS = %w[pre code tt].to_set
def call
process_dollar_pipeline
doc
end
def process_dollar_pipeline
doc.xpath('descendant-or-self::text()').each do |node|
next if has_ancestor?(node, IGNORED_ANCESTOR_TAGS)
node_html = node.to_html
next unless node_html.match?(DOLLAR_INLINE_PATTERN) ||
node_html.match?(DOLLAR_DISPLAY_INLINE_PATTERN)
temp_doc = Nokogiri::HTML.fragment(node_html)
DOLLAR_MATH_PIPELINE.each do |pipeline|
temp_doc.xpath('child::text()').each do |temp_node|
html = temp_node.to_html
temp_node.content.scan(pipeline[:pattern]).each do |matched, math|
html.sub!(matched, math_html(math: math, style: pipeline[:style]))
end
temp_node.replace(html)
end
end
node.replace(temp_doc)
end
end
private
def math_html(math:, style:)
"<code data-math-style=\"#{style}\">#{math}</code>"
end
end
end
end
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