- var_dump: documentation ( source)
<?php
function firstDayOfWeek($date)
{
$day = DateTime::createFromFormat('d-m-Y', $date);
$day->setISODate((int)$day->format('o'), (int)$day->format('W'), 1);
return $day->format('d-m-Y');
}
var_dump(firstDayOfWeek('15-07-2017'));