class SourceEditingPreventSelfXssConstraintValidator

class SourceEditingPreventSelfXssConstraintValidator extends ConstraintValidator {
    use TextEditorObjectDependentValidatorTrait;
    
    /**
     * {@inheritdoc}
     *
     * @throws \Symfony\Component\Validator\Exception\UnexpectedTypeException
     *   Thrown when the given constraint is not supported by this validator.
     */
    public function validate($value, Constraint $constraint) {
        if (!$constraint instanceof SourceEditingPreventSelfXssConstraint) {
            throw new UnexpectedTypeException($constraint, __NAMESPACE__ . '\\SourceEditingPreventSelfXssConstraint');
        }
        if (empty($value)) {
            return;
        }
        $restrictions = HTMLRestrictions::fromString($value);
        // @todo Remove this early return in
        //   https://www.drupal.org/project/drupal/issues/2820364. It is only
        //   necessary because CKEditor5ElementConstraintValidator does not run
        //   before this, which means that this validator cannot assume it receives
        //   valid values.
        if ($restrictions->allowsNothing() || count($restrictions->getAllowedElements()) > 1) {
            return;
        }
        // This validation constraint only validates attributes, not tags; so if all
        // attributes are allowed (TRUE) or no attributes are allowed (FALSE),
        // return early. Only proceed when some attributes are allowed (an array).
        $allowed_elements = $restrictions->getAllowedElements(FALSE);
        assert(count($allowed_elements) === 1);
        $tag = array_key_first($allowed_elements);
        $attribute_restrictions = $allowed_elements[$tag];
        if (!is_array($attribute_restrictions)) {
            return;
        }
        $text_editor = $this->createTextEditorObjectFromContext();
        $text_format_allowed_elements = HTMLRestrictions::fromTextFormat($text_editor->getFilterFormat())
            ->getAllowedElements();
        // Any XSS-prevention related measures imposed by filter plugins are relayed
        // through their ::getHtmlRestrictions() return value. The global attribute
        // `*` HTML tag allows attributes to be forbidden.
        // @see https://html.spec.whatwg.org/multipage/dom.html#global-attributes
        // @see \Drupal\ckeditor5\HTMLRestrictions::validateAllowedRestrictionsPhase4()
        // @see \Drupal\filter\Plugin\Filter\FilterHtml::getHTMLRestrictions()
        $forbidden_attributes = [];
        if (array_key_exists('*', $text_format_allowed_elements)) {
            $forbidden_attributes = array_keys(array_filter($text_format_allowed_elements['*'], function ($attribute_value_restriction, string $attribute_name) {
                return $attribute_value_restriction === FALSE;
            }, ARRAY_FILTER_USE_BOTH));
        }
        foreach ($forbidden_attributes as $forbidden_attribute_name) {
            // Forbidden attributes not containing wildcards, such as `style`.
            if (!self::isWildcardAttributeName($forbidden_attribute_name)) {
                if (array_key_exists($forbidden_attribute_name, $attribute_restrictions)) {
                    $this->context
                        ->buildViolation($constraint->message)
                        ->setParameter('%dangerous_tag', $value)
                        ->addViolation();
                }
            }
            else {
                $regex = self::getRegExForWildCardAttributeName($forbidden_attribute_name);
                if (!empty(preg_grep($regex, array_keys($attribute_restrictions)))) {
                    $this->context
                        ->buildViolation($constraint->message)
                        ->setParameter('%dangerous_tag', $value)
                        ->addViolation();
                }
            }
        }
    }
    
    /**
     * Checks whether the given attribute name contains a wildcard, e.g. `data-*`.
     *
     * @param string $attribute_name
     *   The attribute name to check.
     *
     * @return bool
     *   Whether the given attribute name contains a wildcard.
     */
    private static function isWildcardAttributeName(string $attribute_name) : bool {
        assert($attribute_name !== '*');
        return strpos($attribute_name, '*') !== FALSE;
    }
    
    /**
     * Computes a regular expression for matching a wildcard attribute name.
     *
     * @param string $wildcard_attribute_name
     *   The wildcard attribute name for which to compute a regular expression.
     *
     * @return string
     *   The computed regular expression.
     */
    private static function getRegExForWildCardAttributeName(string $wildcard_attribute_name) : string {
        assert(self::isWildcardAttributeName($wildcard_attribute_name));
        return '/^' . str_replace('*', '.*', $wildcard_attribute_name) . '$/';
    }

}