private function calculateDaysBetween($date1, $date2)
{
$match = '/^\d{4}-\d{1,2}\-\d{1,2}$/';
if (!\preg_match($match, $date1) || !\preg_match($match, $date2)) {
return 0;
}
$d1 = new DateTime($date1);
$d2 = new DateTime($date2);
$diff = $d2->diff($d1);
$days = (float)$diff->format('%a');
if ($diff->invert === 1) {
$days *= -1;
}
return $days;
}