class FormOperations

class FormOperations implements ContainerInjectionInterface {
    
    /**
     * The workspace manager service.
     *
     * @var \Drupal\workspaces\WorkspaceManagerInterface
     */
    protected $workspaceManager;
    
    /**
     * Constructs a new FormOperations instance.
     *
     * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
     *   The workspace manager service.
     */
    public function __construct(WorkspaceManagerInterface $workspace_manager) {
        $this->workspaceManager = $workspace_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('workspaces.manager'));
    }
    
    /**
     * Alters forms to disallow editing in non-default workspaces.
     *
     * @param array $form
     *   An associative array containing the structure of the form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     * @param string $form_id
     *   The form ID.
     *
     * @see hook_form_alter()
     */
    public function formAlter(array &$form, FormStateInterface $form_state, $form_id) {
        // No alterations are needed if we're not in a workspace context.
        if (!$this->workspaceManager
            ->hasActiveWorkspace()) {
            return;
        }
        // Add an additional validation step for every form if we are in a
        // non-default workspace.
        $this->addWorkspaceValidation($form);
        // If a form has already been marked as safe or not to submit in a
        // non-default workspace, we don't have anything else to do.
        if ($form_state->has('workspace_safe')) {
            return;
        }
        // No forms are safe to submit in a non-default workspace by default, except
        // for the whitelisted ones defined below.
        $workspace_safe = FALSE;
        // Whitelist a few forms that we know are safe to submit.
        $form_object = $form_state->getFormObject();
        $is_workspace_form = $form_object instanceof WorkspaceFormInterface;
        $is_search_form = in_array($form_object->getFormId(), [
            'search_block_form',
            'search_form',
        ], TRUE);
        $is_views_exposed_form = $form_object instanceof ViewsExposedForm;
        if ($is_workspace_form || $is_search_form || $is_views_exposed_form) {
            $workspace_safe = TRUE;
        }
        $form_state->set('workspace_safe', $workspace_safe);
    }
    
    /**
     * Adds our validation handler recursively on each element of a form.
     *
     * @param array &$element
     *   An associative array containing the structure of the form.
     */
    protected function addWorkspaceValidation(array &$element) {
        // Recurse through all children and add our validation handler if needed.
        foreach (Element::children($element) as $key) {
            if (isset($element[$key]) && $element[$key]) {
                $this->addWorkspaceValidation($element[$key]);
            }
        }
        if (isset($element['#validate'])) {
            $element['#validate'][] = [
                static::class,
                'validateDefaultWorkspace',
            ];
        }
    }
    
    /**
     * Validation handler which sets a validation error for all unsupported forms.
     */
    public static function validateDefaultWorkspace(array &$form, FormStateInterface $form_state) {
        if ($form_state->get('workspace_safe') !== TRUE) {
            $form_state->setError($form, new TranslatableMarkup('This form can only be submitted in the default workspace.'));
        }
    }

}