Fix PHP datetime time zone.

gistfile1.txt

$wrongDate = new \DateTime('2018-04-25 16:00:00', new \DateTimeZone('+0300'));
// Wed, 25 Apr 2018 16:00:00 +0300

fixZone($wrongDate, new \DateTimeZone('UTC'));
// Wed, 25 Apr 2018 16:00:00 +0000

function fixZone(\DateTime $dateTime, DateTimeZone $rightZone)
{
    $offset     = $dateTime->getOffset();
    $zoneOffset = $rightZone->getOffset($dateTime);

    $diff = $zoneOffset - $offset;

    if ($diff > 0) {
        $dateTime->modify(sprintf('- %d seconds', $diff));
        $dateTime->setTimezone($rightZone);
    }
    if ($diff < 0) {
        $diff = abs($diff);
        $dateTime->modify(sprintf('%d seconds', $diff));
        $dateTime->setTimezone($rightZone);
    }
}