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require 'rouge/plugins/redcarpet'
module Banzai
module Filter
# HTML Filter to highlight fenced code blocks
#
class SyntaxHighlightFilter < HTML::Pipeline::Filter
include Rouge::Plugins::Redcarpet
def call
doc.search('pre > code').each do |node|
highlight_node(node)
end
doc
end
def highlight_node(node)
language = node.attr('class')
code = node.text
css_classes = "code highlight"
lexer = lexer_for(language)
begin
code = format(lex(lexer, code))
css_classes << " js-syntax-highlight #{lexer.tag}"
rescue
# Gracefully handle syntax highlighter bugs/errors to ensure
# users can still access an issue/comment/etc.
end
highlighted = %(<pre class="#{css_classes}" v-pre="true"><code>#{code}</code></pre>)
# Extracted to a method to measure it
replace_parent_pre_element(node, highlighted)
end
private
# Separate method so it can be instrumented.
def lex(lexer, code)
lexer.lex(code)
end
def format(tokens)
rouge_formatter.format(tokens)
end
def lexer_for(language)
(Rouge::Lexer.find(language) || Rouge::Lexers::PlainText).new
end
def replace_parent_pre_element(node, highlighted)
# Replace the parent `pre` element with the entire highlighted block
node.parent.replace(highlighted)
end
# Override Rouge::Plugins::Redcarpet#rouge_formatter
def rouge_formatter(lexer = nil)
@rouge_formatter ||= Rouge::Formatters::HTML.new
end
end
end
end
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