class String

  def old_snake_case
    gsub(/\B[A-Z]/, '_\&').downcase
  end

  def new_snake_case
    if self =~ /^[A-Z]+$/
      return self.downcase
    else
      self.gsub(/([A-Z]{1,})(?=[A-Z][a-z]?)/) do |m|
        m.capitalize
      end.gsub(/\B[A-Z]/, '_\&').downcase
    end
  end

  def matt_snake_case
    return self.downcase if self =~ /^[A-Z]+$/
    self.gsub(/([A-Z]+)(?=[A-Z][a-z]?)|\B[A-Z]/, '_\&') =~ /_*(.*)/
      return $+.downcase
  end

end

puts 'RequestURITooLarge'.new_snake_case
puts 'HTTPVersionNotSupported'.new_snake_case
puts 'OK'.new_snake_case
puts 'CNNNews'.new_snake_case
puts "HTTPVersionURINotCompatible".new_snake_case
puts "HeadlineCNNNews".new_snake_case

# >> request_uri_too_large
# >> http_version_not_supported
# >> ok
# >> cnn_news
# >> http_version_uri_not_compatible
# >> headline_cnn_news

puts 'RequestURITooLarge'.matt_snake_case
puts 'HTTPVersionNotSupported'.matt_snake_case
puts 'OK'.matt_snake_case
puts 'CNNNews'.matt_snake_case
puts "HTTPVersionURINotCompatible".matt_snake_case
puts "HeadlineCNNNews".matt_snake_case

# >> request_uri_too_large
# >> http_version_not_supported
# >> ok
# >> cnn_news
# >> http_version_uri_not_compatible
# >> headline_cnn_news