interface WidgetBaseInterface

interface WidgetBaseInterface extends PluginSettingsInterface {
    
    /**
     * Creates a form element for a field.
     *
     * If the entity associated with the form is new (i.e., $entity->isNew() is
     * TRUE), the 'default value', if any, is pre-populated. Also allows other
     * modules to alter the form element by implementing their own hooks.
     *
     * @param \Drupal\Core\Field\FieldItemListInterface $items
     *   An array of the field values. When creating a new entity this may be NULL
     *   or an empty array to use default values.
     * @param array $form
     *   An array representing the form that the editing element will be attached
     *   to.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     * @param int $get_delta
     *   Used to get only a specific delta value of a multiple value field.
     *
     * @return array
     *   The form element array created for this field.
     */
    public function form(FieldItemListInterface $items, array &$form, FormStateInterface $form_state, $get_delta = NULL);
    
    /**
     * Extracts field values from submitted form values.
     *
     * @param \Drupal\Core\Field\FieldItemListInterface $items
     *   The field values. This parameter is altered by reference to receive the
     *   incoming form values.
     * @param array $form
     *   The form structure where field elements are attached to. This might be a
     *   full form structure, or a sub-element of a larger form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The form state.
     */
    public function extractFormValues(FieldItemListInterface $items, array $form, FormStateInterface $form_state);
    
    /**
     * Reports field-level validation errors against actual form elements.
     *
     * @param \Drupal\Core\Field\FieldItemListInterface $items
     *   The field values.
     * @param \Symfony\Component\Validator\ConstraintViolationListInterface $violations
     *   A list of constraint violations to flag.
     * @param array $form
     *   The form structure where field elements are attached to. This might be a
     *   full form structure, or a sub-element of a larger form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The form state.
     */
    public function flagErrors(FieldItemListInterface $items, ConstraintViolationListInterface $violations, array $form, FormStateInterface $form_state);
    
    /**
     * Retrieves processing information about the widget from $form_state.
     *
     * This method is static so that it can be used in static Form API callbacks.
     *
     * @param array $parents
     *   The array of #parents where the field lives in the form.
     * @param string $field_name
     *   The field name.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The form state.
     *
     * @return array
     *   An array with the following key/value pairs:
     *   - items_count: The number of widgets to display for the field.
     *   - array_parents: The location of the field's widgets within the $form
     *     structure. This entry is populated at '#after_build' time.
     */
    public static function getWidgetState(array $parents, $field_name, FormStateInterface $form_state);
    
    /**
     * Stores processing information about the widget in $form_state.
     *
     * This method is static so that it can be used in static Form API #callbacks.
     *
     * @param array $parents
     *   The array of #parents where the widget lives in the form.
     * @param string $field_name
     *   The field name.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The form state.
     * @param array $field_state
     *   The array of data to store. See getWidgetState() for the structure and
     *   content of the array.
     */
    public static function setWidgetState(array $parents, $field_name, FormStateInterface $form_state, array $field_state);

}