interface EntityFormDisplayInterface

interface EntityFormDisplayInterface extends EntityDisplayInterface {
    
    /**
     * Adds field widgets to an entity form.
     *
     * The form elements for the entity's fields are added by reference as direct
     * children in the $form parameter. This parameter can be a full form
     * structure (most common case for entity edit forms), or a sub-element of a
     * larger form.
     *
     * By default, submitted field values appear at the top-level of
     * $form_state->getValues(). A different location within
     * $form_state->getValues() can be specified by setting the '#parents'
     * property on the incoming $form parameter. Because of name clashes, two
     * instances of the same field cannot appear within the same $form element, or
     * within the same '#parents' space.
     *
     * Sample resulting structure in $form:
     * @code
     *   '#parents' => The location of field values in $form_state->getValues(),
     *   '#entity_type' => The name of the entity type,
     *   '#bundle' => The name of the bundle,
     *   // One sub-array per field appearing in the entity, keyed by field name.
     *   // The structure of the array differs slightly depending on whether the
     *   // widget is 'single-value' (provides the input for one field value,
     *   // most common case), and will therefore be repeated as many times as
     *   // needed, or 'multiple-values' (one single widget allows the input of
     *   // several values; e.g., checkboxes, select box, etc.).
     *   'field_foo' => array(
     *     '#access' => TRUE if the current user has 'edit' grants for the field,
     *       FALSE if not.
     *     'widget' => array(
     *       '#field_name' => The name of the field,
     *       '#title' => The label of the field,
     *       '#description' => The description text for the field,
     *       '#required' => Whether or not the field is required,
     *       '#field_parents' => The 'parents' space for the field in the form,
     *          equal to the #parents property of the $form parameter received by
     *          this method,
     *
     *       // For 'multiple-value' widgets, the remaining elements in the
     *       // sub-array depend on the widget.
     *
     *       // For 'single-value' widgets:
     *       '#theme' => 'field_multiple_value_form',
     *       '#cardinality' => The field cardinality,
     *       '#cardinality_multiple' => TRUE if the field can contain multiple
     *         items, FALSE otherwise.
     *       // One sub-array per copy of the widget, keyed by delta.
     *       0 => array(
     *         '#title' => The title to be displayed by the widget,
     *         '#description' => The description text for the field,
     *         '#required' => Whether the widget should be marked required,
     *         '#delta' => 0,
     *         '#weight' => 0,
     *         '#field_parents' => Same as above,
     *         // The remaining elements in the sub-array depend on the widget.
     *         ...
     *       ),
     *       1 => array(
     *         ...
     *       ),
     *       ...
     *     ),
     *     ...
     *   ),
     * )
     * @endcode
     *
     * Additionally, some processing data is placed in $form_state, and can be
     * accessed by \Drupal\Core\Field\WidgetBaseInterface::getWidgetState() and
     * \Drupal\Core\Field\WidgetBaseInterface::setWidgetState().
     *
     * @param \Drupal\Core\Entity\FieldableEntityInterface $entity
     *   The entity.
     * @param array $form
     *   The form structure to fill in. This can be a full form structure, or a
     *   sub-element of a larger form. The #parents property can be set to
     *   control the location of submitted field values within
     *   $form_state->getValues(). If not specified, $form['#parents'] is set to
     *   an empty array, which results in field values located at the top-level of
     *   $form_state->getValues().
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The form state.
     */
    public function buildForm(FieldableEntityInterface $entity, array &$form, FormStateInterface $form_state);
    
    /**
     * Extracts field values from the submitted widget values into the entity.
     *
     * This accounts for drag-and-drop reordering of field values, and filtering
     * of empty values.
     *
     * @param \Drupal\Core\Entity\FieldableEntityInterface $entity
     *   The entity.
     * @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.
     *
     * @return array
     *   An array whose keys and values are the keys of the top-level entries in
     *   $form_state->getValues() that have been processed. The remaining entries,
     *   if any, do not correspond to widgets and should be extracted manually by
     *   the caller if needed.
     */
    public function extractFormValues(FieldableEntityInterface $entity, array &$form, FormStateInterface $form_state);
    
    /**
     * Validates submitted widget values and sets the corresponding form errors.
     *
     * This method invokes entity validation and takes care of flagging them on
     * the form. This is particularly useful when all elements on the form are
     * managed by the form display.
     *
     * As an alternative, entity validation can be invoked separately such that
     * some violations can be flagged manually. In that case
     * \Drupal\Core\Entity\Display\EntityFormDisplayInterface::flagViolations()
     * must be used for flagging violations related to the form display.
     *
     * Note that there are two levels of validation for fields in forms: widget
     * validation and field validation:
     * - Widget validation steps are specific to a given widget's own form
     *   structure and UI metaphors. They are executed during normal form
     *   validation, usually through Form API's #element_validate property.
     *   Errors reported at this level are typically those that prevent the
     *   extraction of proper field values from the submitted form input.
     * - If no form / widget errors were reported for the field, field validation
     *   steps are performed according to the "constraints" specified by the
     *   field definition as part of the entity validation. That validation is
     *   independent of the specific widget being used in a given form, and is
     *   also performed on REST entity submissions.
     *
     * @param \Drupal\Core\Entity\FieldableEntityInterface $entity
     *   The entity.
     * @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 validateFormValues(FieldableEntityInterface $entity, array &$form, FormStateInterface $form_state);
    
    /**
     * Flags entity validation violations as form errors.
     *
     * This method processes all violations passed, thus any violations not
     * related to fields of the form display must be processed before this method
     * is invoked.
     *
     * The method flags constraint violations related to fields shown on the
     * form as form errors on the correct form elements. Possibly pre-existing
     * violations of hidden fields (so fields not appearing in the display) are
     * ignored. Other, non-field related violations are passed through and set as
     * form errors according to the property path of the violations.
     *
     * @param \Drupal\Core\Entity\EntityConstraintViolationListInterface $violations
     *   The 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 flagWidgetsErrorsFromViolations(EntityConstraintViolationListInterface $violations, array &$form, FormStateInterface $form_state);

}