class Asciidoctor::Document

def fill_datetime_attributes attrs, input_mtime
  # See https://reproducible-builds.org/specs/source-date-epoch/
  now = (::ENV.key? 'SOURCE_DATE_EPOCH') ? (source_date_epoch = (::Time.at Integer ::ENV['SOURCE_DATE_EPOCH']).utc) : ::Time.now
  if (localdate = attrs['localdate'])
    attrs['localyear'] ||= (localdate.index '-') == 4 ? (localdate.slice 0, 4) : nil
  else
    localdate = attrs['localdate'] = now.strftime '%F'
    attrs['localyear'] ||= now.year.to_s
  end
  # %Z is OS dependent and may contain characters that aren't UTF-8 encoded (see asciidoctor#2770 and asciidoctor.js#23)
  localtime = (attrs['localtime'] ||= now.strftime %(%T #{now.utc_offset == 0 ? 'UTC' : '%z'}))
  attrs['localdatetime'] ||= %(#{localdate} #{localtime})
  # docdate, doctime and docdatetime should default to localdate, localtime and localdatetime if not otherwise set
  input_mtime = source_date_epoch || input_mtime || now
  if (docdate = attrs['docdate'])
    attrs['docyear'] ||= ((docdate.index '-') == 4 ? (docdate.slice 0, 4) : nil)
  else
    docdate = attrs['docdate'] = input_mtime.strftime '%F'
    attrs['docyear'] ||= input_mtime.year.to_s
  end
  # %Z is OS dependent and may contain characters that aren't UTF-8 encoded (see asciidoctor#2770 and asciidoctor.js#23)
  doctime = (attrs['doctime'] ||= input_mtime.strftime %(%T #{input_mtime.utc_offset == 0 ? 'UTC' : '%z'}))
  attrs['docdatetime'] ||= %(#{docdate} #{doctime})
  nil
end