def to_seconds(base = nil)
      rest = [weeks, days, hours, minutes, seconds].map(&:to_seconds)

      years.to_seconds(base) + months_to_seconds(base) + rest.reduce(&:+)
    end
def to_seconds(base = nil)
      rest = [weeks, days, hours, minutes, seconds].map(&:to_seconds)

      years.to_seconds(base) + months_to_seconds(base) + rest.reduce(&:+)
    end
@param [ISO8601::DateTime, nil] base (nil) The base datetime to
   calculate the duration against an specific point in time.

 @return [Numeric] The duration in seconds