class TimeSpan

class TimeSpan extends IntegerData implements DurationInterface {
    
    /**
     * {@inheritdoc}
     */
    public function getDuration() {
        if ($this->value) {
            // Keep the duration in seconds as there is generally no valid way to
            // convert it to days, months or years.
            return new \DateInterval('PT' . $this->value . 'S');
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function setDuration(\DateInterval $duration, $notify = TRUE) {
        // Note that this applies the assumption of 12 month's a 30 days and
        // each year having 365 days. There is no accurate conversion for time spans
        // exceeding a day.
        $this->value = $duration->y * 365 * 24 * 60 * 60 + $duration->m * 30 * 24 * 60 * 60 + $duration->d * 24 * 60 * 60 + $duration->h * 60 * 60 + $duration->i * 60 + $duration->s;
        // Notify the parent of any changes.
        if ($notify && isset($this->parent)) {
            $this->parent
                ->onChange($this->name);
        }
    }

}