get start and end date

$date = '28-02-2015'
$nextDateWeek = new \DateTime(date('Y-m-d', strtotime($date . '+1 week')));
$lastDateWeek = new \DateTime(date('Y-m-d', strtotime($date . '-1 week')));
$lastWeek = $nextDateWeek->format("W");
$nextWeek = $lastDateWeek->format("W");
$selectedYear = date('Y', strtotime($date));

$nextWeekDays = Common::getStartAndEndDate($nextWeek, $selectedYear);
$lastWeekDays = Common::getStartAndEndDate($lastWeek, $selectedYear);

public static function getStartAndEndDate($week, $year)
{
    $dto = new \DateTime();
    $dto->setISODate($year, $week);
    $ret['firstDay'] = $dto->format('d-m-Y');
    $dto->modify('+6 days');
    $ret['lastDay'] = $dto->format('d-m-Y');
    return $ret;
}