- var_dump: documentation ( source)
- strftime: documentation ( source)
- str_replace: documentation ( source)
- date: documentation ( source)
<?php
$sourceFormat = 'd-m-Y';
$targetFormat = 'Y-m-d';
$value = '22-11-2017';
$datetime = \DateTime::createFromFormat($sourceFormat, $value, new \DateTimeZone('UTC'));
$targetFormat = str_replace('%e', date('j', $datetime->getTimestamp()), $targetFormat);
$output = strftime($targetFormat, $datetime->getTimestamp());
var_dump($output);