private function next($dayOfWeek)
    {
        $days = [
            self::SUNDAY    => 'Sunday',
            self::MONDAY    => 'Monday',
            self::TUESDAY   => 'Tuesday',
            self::WEDNESDAY => 'Wednesday',
            self::THURSDAY  => 'Thursday',
            self::FRIDAY    => 'Friday',
            self::SATURDAY  => 'Saturday',
        ];

        $dow = $days[$dayOfWeek];

        return $this->startOfDay()->modify("next $dow");
    }