module Lograge
  module Formatters
    class Graylog2
      def call(data)
        # Cloning because we don't want to mess with the original when mutating keys.
        data_clone = data.clone

        base = {
          short_message: short_message(data_clone)
        }

        # Add underscore to every key to follow GELF additional field syntax.
        data_clone.keys.each do |key|
          data_clone[underscore_prefix(key)] = data_clone[key]
          data_clone.delete(key)
        end

        data_clone.merge(base)
      end

      def underscore_prefix(key)
        "_#{key}".to_sym
      end

      def short_message(data)
        "[#{data[:status]}] #{data[:method]} #{data[:path]} (#{data[:controller]}##{data[:action]})"
      end
    end
  end
end