Simple conversion of WordPress i18n date format to jQuery UI Datepicker format

convert_date_format_to_jqueryui_datepicker.php

<?php
/**
 * Converts a given WordPress date format to jQuery UI Datepicker format.
 *
 * @author  Denison Martins <[email protected]>
 *
 * @see     https://codex.wordpress.org/Formatting_Date_and_Time
 * @see     http://api.jqueryui.com/datepicker
 *
 * @throws  InvalidArgumentException
 *
 * @param   string  $date_format_original
 *
 * @return  string
 */
function convert_date_format_to_jqueryui_datepicker($date_format_original)
{
    if (!is_string($date_format_original)) {
        throw new \InvalidArgumentException('The supplied parameter must be a string.');
    }

    if (!preg_match_all('/([\w])/', $date_format_original, $current_date_format_terms)) {
        return $date_format_original;
    }

    $format_terms_map = [
        'j' => 'd',
        'd' => 'dd',
        'l' => 'DD',
        'n' => 'm',
        'm' => 'mm',
        'F' => 'MM',
        'Y' => 'yy',
        'U' => '@',
    ];

    return array_reduce(
        array_unique($current_date_format_terms[0]),
        function($new_format, $format_term_needle) use ($format_terms_map) {
            if (!isset($format_terms_map[$format_term_needle])) {
                return $new_format;
            }

            return str_replace($format_term_needle, $format_terms_map[$format_term_needle], $new_format);
        },
        $date_format_original
    );
}