module LibvirtAsync
  class LogFormatter
    LOG_FORMAT = "%s, %s [%d/%s/%s] %s\n".freeze
    DEFAULT_DATETIME_FORMAT = "%F %T.%N".freeze

    attr_accessor :datetime_format

    def initialize
      @datetime_format = nil
    end

    def call(severity, time, progname, message)
      LOG_FORMAT % [
          severity[0..0],
          format_datetime(time),
          Process.pid,
          "0x#{Fiber.current.object_id.to_s(16)}",
          progname,
          format_message(message)
      ]
    end

    private

    def format_datetime(time)
      time.strftime(@datetime_format || DEFAULT_DATETIME_FORMAT)
    end

    def format_message(message)
      case message
      when ::String
        message
      when ::Exception
        "<#{message.class}>:#{message.message}\n#{(message.backtrace || []).join("\n")}"
      else
        message.inspect
      end
    end
  end
end