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require 'uri'
module Banzai
module Filter
# HTML filter that adds class="code math" and removes the dollar sign in $`2+2`$.
#
class MathFilter < HTML::Pipeline::Filter
# This picks out <code>...</code>.
INLINE_MATH = 'descendant-or-self::code'.freeze
# Pick out a code block which is declared math
DISPLAY_MATH = "descendant-or-self::pre[contains(@class, 'math') and contains(@class, 'code')]".freeze
# Attribute indicating inline or display math.
STYLE_ATTRIBUTE = 'data-math-style'.freeze
# Class used for tagging elements that should be rendered
TAG_CLASS = 'js-render-math'.freeze
INLINE_CLASSES = "code math #{TAG_CLASS}".freeze
DOLLAR_SIGN = '$'.freeze
def call
doc.xpath(INLINE_MATH).each do |code|
closing = code.next
opening = code.previous
# We need a sibling before and after.
# They should end and start with $ respectively.
if closing && opening &&
closing.content.first == DOLLAR_SIGN &&
opening.content.last == DOLLAR_SIGN
code[:class] = INLINE_CLASSES
code[STYLE_ATTRIBUTE] = 'inline'
closing.content = closing.content[1..-1]
opening.content = opening.content[0..-2]
end
end
doc.xpath(DISPLAY_MATH).each do |el|
el[STYLE_ATTRIBUTE] = 'display'
el[:class] += " #{TAG_CLASS}"
end
doc
end
end
end
end
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