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# frozen_string_literal: true
module Banzai
module Filter
class FrontMatterFilter < HTML::Pipeline::Filter
DELIM_LANG = {
'---' => 'yaml',
'+++' => 'toml',
';;;' => 'json'
}.freeze
DELIM = Regexp.union(DELIM_LANG.keys)
PATTERN = %r{
\A(?:[^\r\n]*coding:[^\r\n]*)? # optional encoding line
\s*
^(?<delim>#{DELIM})[ \t]*(?<lang>\S*) # opening front matter marker (optional language specifier)
\s*
^(?<front_matter>.*?) # front matter (not greedy)
\s*
^\k<delim> # closing front matter marker
\s*
}mx.freeze
def call
html.sub(PATTERN) do |_match|
lang = $~[:lang].presence || DELIM_LANG[$~[:delim]]
["```#{lang}", $~[:front_matter], "```", "\n"].join("\n")
end
end
end
end
end
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