interface FormSubmitterInterface

interface FormSubmitterInterface {
    
    /**
     * Handles the submitted form, executing callbacks and processing responses.
     *
     * @param array $form
     *   An associative array containing the structure of the form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     *
     * @return null|\Symfony\Component\HttpFoundation\Response
     *   If a response was set by a submit handler, or if the form needs to
     *   redirect, a Response object will be returned.
     */
    public function doSubmitForm(&$form, FormStateInterface &$form_state);
    
    /**
     * Executes custom submission handlers for a given form.
     *
     * Button-specific handlers are checked first. If none exist, the function
     * falls back to form-level handlers.
     *
     * @param $form
     *   An associative array containing the structure of the form.
     * @param $form_state
     *   The current state of the form. If the user submitted the form by clicking
     *   a button with custom handler functions defined, those handlers will be
     *   stored here.
     */
    public function executeSubmitHandlers(&$form, FormStateInterface &$form_state);
    
    /**
     * Redirects the user to a URL after a form has been processed.
     *
     * After a form is submitted and processed, normally the user should be
     * redirected to a new destination page. This function figures out what that
     * destination should be, based on the $form_state and the 'destination'
     * query string in the request URL, and redirects the user there.
     *
     * The result of \Drupal\Core\Form|FormStateInterface::getRedirect()
     * determines where to redirect the user. See the possible return values
     * listed there. If the result is FALSE, then the user will not be redirected.
     *
     * Here is an example of how to set up a form to redirect to the path 'user':
     * @code
     * $form_state->setRedirect('user.page');
     * @endcode
     * And here is an example of how to redirect to 'node/123?foo=bar#baz':
     * @code
     * $form_state->setRedirect('entity.node.canonical',
     *   array('node' => 123),
     *   array(
     *     'query' => array(
     *       'foo' => 'bar',
     *     ),
     *     'fragment' => 'baz',
     *   ),
     * );
     * @endcode
     *
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     *
     * @return \Symfony\Component\HttpFoundation\RedirectResponse|null
     *
     * @see \Drupal\Core\Form\FormBuilderInterface::processForm()
     * @see \Drupal\Core\Form\FormBuilderInterface::buildForm()
     */
    public function redirectForm(FormStateInterface $form_state);

}