datetimehelper.php

<?php

class DateTimeHelper {

    /**
     * @param array $dateintervals Array of \DateInterval
     * @return \DateInterval
     */
    public function calculateIntervalAverage($dateintervals)
    {
        $offset = new \DateTime('@0');

        foreach ($dateintervals as $interval)
            $offset->add($interval);

        $averageSeconds = round($offset->getTimestamp() / count($dateintervals));

        $today = new \DateTime('@0');
        $datetime = new \DateTime('@0');
        $datetime->setTime(0, 0, $averageSeconds);

        return $datetime->diff($today);
    }

    /**
     * @param array $dateIntervals Array of \DateInterval
     * @return \DateInterval|null
     */
    public function calculateIntervalMin($dateIntervals)
    {
        $min = null;

        foreach ($dateIntervals as $interval)
        {
            $dateTimeInterval = new \DateTime('@0');
            $dateTimeInterval->add($interval);
            
            if ($min == null) {
                $min = $interval;
                continue;
            }

            $emptyDateTime = new \DateTime('@0');
            $emptyDateTime->add($min);

            if ($emptyDateTime > $dateTimeInterval)
                $min = $interval;
        }

        return $min;
    }

    /**
     * @param array $dateIntervals Array of \DateInterval
     * @return \DateInterval|null
     */
    public function calculateIntervalMax($dateIntervals)
    {
        $max = null;

        foreach ($dateIntervals as $interval)
        {
            $dateTimeInterval = new \DateTime('@0');
            $dateTimeInterval->add($interval);
            
            if ($max == null) {
                $max = $interval;
                continue;
            }

            $emptyDateTime = new \DateTime('@0');
            $emptyDateTime->add($max);

            if ($emptyDateTime < $dateTimeInterval)
                $max = $interval;
        }

        return $max;
    }
}