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# frozen_string_literal: true
module Banzai
module Filter
# In order to allow a user to short-circuit our reference shortcuts
# (such as # or !), the user should be able to escape them, like \#.
# CommonMark supports this, however it removes all information about
# what was actually a literal. In order to short-circuit the reference,
# we must surround backslash escaped ASCII punctuation with a custom sequence.
# This way CommonMark will properly handle the backslash escaped chars
# but we will maintain knowledge (the sequence) that it was a literal.
#
# We need to surround the character, not just prefix it. It could
# get converted into an entity by CommonMark and we wouldn't know how many
# characters there are. The entire literal needs to be surrounded with
# a `span` tag, which short-circuits our reference processing.
#
# We can't use a custom HTML tag since we could be initially surrounding
# text in an href, and then CommonMark will not be able to parse links
# properly. So we use `cmliteral-` and `-cmliteral`
#
# https://spec.commonmark.org/0.29/#backslash-escapes
#
# This filter does the initial surrounding, and MarkdownPostEscapeFilter
# does the conversion into span tags.
class MarkdownPreEscapeFilter < HTML::Pipeline::TextFilter
# We just need to target those that are special GitLab references
REFERENCE_CHARACTERS = '@#!$&~%^'
ASCII_PUNCTUATION = %r{(\\[#{REFERENCE_CHARACTERS}])}.freeze
LITERAL_KEYWORD = 'cmliteral'
def call
@text.gsub(ASCII_PUNCTUATION) do |match|
# The majority of markdown does not have literals. If none
# are found, we can bypass the post filter
result[:escaped_literals] = true
"#{LITERAL_KEYWORD}-#{match}-#{LITERAL_KEYWORD}"
end
end
end
end
end
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