<?php
/**
 * @package     Joomla.Site
 * @subpackage  com_users
 *
 * @copyright   2022 Francesco Potortì
 * @license     GNU General Public License version 2 or later; see LICENSE.txt
 */
defined('JPATH_PLATFORM') or die;

use Joomla\Registry\Registry;
class JFormRuleUserNamePot extends JFormRule
{
    /**
     * Test for sane usernames.
     *
     * Tested under Joomla 3.9
     * To use this rule, the form XML (for example components/com_users/models/forms/registration.xml)
     * needs this:
     * <fieldset name="form_name" addrulepath="components/com_users/models/rules"> </fieldset>
     *
     * and the input (text) field needs this:
     * validate="usernamepot" (basename of this file, under components/com_users/models/rules/)
     * maxlength=10 (recommended, but any number > 0 will do)
     * pcrepattern="/^[0-9a-bA-B]+$/" (recommended, any PCRE will do)
     * validatemessage="User name can only contain letters and numbers" (recommended)
     *
     * @param   SimpleXMLElement  $element  The SimpleXMLElement object representing the `<field>` tag for the form field object.
     * @param   mixed             $value    The form field value to validate.
     * @param   string            $group    The field name group control value. This acts as an array container for the field.
     *                                      For example if the field has name="foo" and the group value is set to "bar" then the
     *                                      full field name would end up being "bar[foo]".
     * @param   Registry          $input    An optional Registry object with the entire data set to validate against the entire form.
     * @param   JForm             $form     The form object for which the field is being tested.
     *
     * @return  boolean  True if the value is valid, false otherwise.
     *
     * @since   3.9
     */
    public function test(SimpleXMLElement $element, $value, $group = null, Registry $input = null, JForm $form = null)
    {
        $maxlen = (int) $element->attributes()->maxlength;
        $pattern = $element->attributes()->pcrepattern;
        $errormessage = $element->attributes()->validatemessage;

        // throw new InvalidArgumentException(sprintf('maxlen=%d, pattern=%s, message=%s', $maxlen, $pattern, $element->attributes()->message));
        
        if (strlen($value) <= $maxlen and preg_match($pattern, $value) === 1)
        {
            return true;
        }

        $element->attributes()->message = $errormessage;
        return false;
    }
}

<?php
/**
 * @package     Joomla.Site
 * @subpackage  com_users
 *
 * @copyright   2022 Francesco Potortì
 * @license     GNU General Public License version 2 or later; see LICENSE.txt
 */
defined('JPATH_PLATFORM') or die;

use Joomla\Registry\Registry;
class JFormRuleUserNamePot extends JFormRule
{
    /**
     * Test for sane usernames.
     *
     * Tested under Joomla 3.9
     * To use this rule, the form XML (for example components/com_users/models/forms/registration.xml)
     * needs this:
     * <fieldset name="form_name" addrulepath="components/com_users/models/rules"> </fieldset>
     *
     * and the input (text) field needs this:
     * validate="usernamepot" (basename of this file, under components/com_users/models/rules/)
     * maxlength=10 (recommended, but any number > 0 will do)
     * pcrepattern="/^[0-9a-zA-Z]+$/" (recommended, any PCRE will do)
     * validatemessage="User name can only contain letters and numbers" (recommended)
     *
     * @param   SimpleXMLElement  $element  The SimpleXMLElement object representing the `<field>` tag for the form field object.
     * @param   mixed             $value    The form field value to validate.
     * @param   string            $group    The field name group control value. This acts as an array container for the field.
     *                                      For example if the field has name="foo" and the group value is set to "bar" then the
     *                                      full field name would end up being "bar[foo]".
     * @param   Registry          $input    An optional Registry object with the entire data set to validate against the entire form.
     * @param   JForm             $form     The form object for which the field is being tested.
     *
     * @return  boolean  True if the value is valid, false otherwise.
     *
     * @since   3.9
     */
    public function test(SimpleXMLElement $element, $value, $group = null, Registry $input = null, JForm $form = null)
    {
        $maxlen = (int) $element->attributes()->maxlength;
        $pattern = $element->attributes()->pcrepattern;
        $errormessage = $element->attributes()->validatemessage;

        // throw new InvalidArgumentException(sprintf('maxlen=%d, pattern=%s, message=%s', $maxlen, $pattern, $element->attributes()->message));
        
        if (strlen($value) <= $maxlen and preg_match($pattern, $value) === 1)
        {
            return true;
        }

        $element->attributes()->message = $errormessage;
        return false;
    }
}