public static function getDateIntervalSpec(DateInterval $interval)
    {
        $date = array_filter([
            static::PERIOD_YEARS => abs($interval->y),
            static::PERIOD_MONTHS => abs($interval->m),
            static::PERIOD_DAYS => abs($interval->d),
        ]);

        $time = array_filter([
            static::PERIOD_HOURS => abs($interval->h),
            static::PERIOD_MINUTES => abs($interval->i),
            static::PERIOD_SECONDS => abs($interval->s),
        ]);

        $specString = static::PERIOD_PREFIX;

        foreach ($date as $key => $value) {
            $specString .= $value.$key;
        }

        if (count($time) > 0) {
            $specString .= static::PERIOD_TIME_PREFIX;
            foreach ($time as $key => $value) {
                $specString .= $value.$key;
            }
        }

        return $specString === static::PERIOD_PREFIX ? 'PT0S' : $specString;
    }