class ToolbarItemConstraintValidator

class ToolbarItemConstraintValidator extends ConstraintValidator implements ContainerInjectionInterface {
    use PluginManagerDependentValidatorTrait;
    
    /**
     * {@inheritdoc}
     *
     * @throws \Symfony\Component\Validator\Exception\UnexpectedTypeException
     *   Thrown when the given constraint is not supported by this validator.
     */
    public function validate($toolbar_item, Constraint $constraint) {
        if (!$constraint instanceof ToolbarItemConstraint) {
            throw new UnexpectedTypeException($constraint, __NAMESPACE__ . '\\ToolbarItem');
        }
        if ($toolbar_item === NULL) {
            return;
        }
        if (!static::isValidToolbarItem($toolbar_item)) {
            $this->context
                ->buildViolation($constraint->message)
                ->setParameter('%toolbar_item', $toolbar_item)
                ->setInvalidValue($toolbar_item)
                ->addViolation();
        }
    }
    
    /**
     * Validates the given toolbar item.
     *
     * @param string $toolbar_item
     *   A toolbar item as expected by CKEditor 5.
     *
     * @return bool
     *   Whether the given toolbar item is valid or not.
     */
    protected function isValidToolbarItem(string $toolbar_item) : bool {
        // Special case: the toolbar group separator.
        // @see https://ckeditor.com/docs/ckeditor5/latest/features/toolbar/toolbar.html#separating-toolbar-items
        if ($toolbar_item === '|') {
            return TRUE;
        }
        // Special case: the breakpoint separator.
        // @see https://ckeditor.com/docs/ckeditor5/latest/features/toolbar/toolbar.html#explicit-wrapping-breakpoint
        if ($toolbar_item === '-') {
            return TRUE;
        }
        $available_toolbar_items = array_keys($this->pluginManager
            ->getToolbarItems());
        return in_array($toolbar_item, $available_toolbar_items, TRUE);
    }

}