This MODX Snippet convert german date DD.MM.YYYY to YYYY-MM-DD

dateconvert.php

<?php
/**
 * dateConvert
 *
 * DESCRIPTION
 *
 * This Snippet convert DD.MM.YYYY to YYYY-MM-DD
 *
 * PROPERTIES:
 *
 * &input required
 * &options required
 *
 * USAGE:
 *
 * [[+date:dateConvert=`%Y-%m-%d`]]
 *
 */

# vars
$input = $modx->getOption('input', $scriptProperties, false);

# split string
if ($input) {
    list($d, $m, $y) = explode('.', $input);
    $time = strtotime($y . '-' . $m . '-' . $d);
} else {
    $time = time();
}

return strftime($options, $time);