<?php

namespace Drupal\Core\Field;

use Drupal\Core\Form\FormStateInterface;
use Symfony\Component\Validator\ConstraintViolationInterface;

/**
 * Interface definition for field widget plugins.
 *
 * This interface details the methods that most plugin implementations will want
 * to override. See Drupal\Core\Field\WidgetBaseInterface for base
 * wrapping methods that should most likely be inherited directly from
 * Drupal\Core\Field\WidgetBase..
 *
 * @ingroup field_widget
 */
interface WidgetInterface extends WidgetBaseInterface {

  /**
   * Returns a form to configure settings for the widget.
   *
   * Invoked from \Drupal\field_ui\Form\EntityDisplayFormBase to allow
   * administrators to configure the widget. The field_ui module takes care of
   * handling submitted form values.
   *
   * @param array $form
   *   The form where the settings form is being included in.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   *
   * @return array
   *   The form definition for the widget settings.
   */
  public function settingsForm(array $form, FormStateInterface $form_state);

  /**
   * Returns a short summary for the current widget settings.
   *
   * If an empty result is returned, a UI can still be provided to display
   * a settings form in case the widget has configurable settings.
   *
   * @return array
   *   A short summary of the widget settings.
   */
  public function settingsSummary();

  /**
   * Returns the form for a single field widget.
   *
   * Field widget form elements should be based on the passed-in $element, which
   * contains the base form element properties derived from the field
   * configuration.
   *
   * The BaseWidget methods will set the weight, field name and delta values for
   * each form element. If there are multiple values for this field, the
   * formElement() method will be called as many times as needed.
   *
   * Other modules may alter the form element provided by this function using
   * hook_field_widget_single_element_form_alter() or
   * hook_field_widget_single_element_WIDGET_TYPE_form_alter().
   *
   * The FAPI element callbacks (such as #process, #element_validate,
   * #value_callback, etc.) used by the widget do not have access to the
   * original $field_definition passed to the widget's constructor. Therefore,
   * if any information is needed from that definition by those callbacks, the
   * widget implementing this method, or a
   * hook_field_widget[_WIDGET_TYPE]_form_alter() implementation, must extract
   * the needed properties from the field definition and set them as ad-hoc
   * $element['#custom'] properties, for later use by its element callbacks.
   *
   * @param \Drupal\Core\Field\FieldItemListInterface $items
   *   Array of default values for this field.
   * @param int $delta
   *   The order of this item in the array of sub-elements (0, 1, 2, etc.).
   * @param array $element
   *   A form element array containing basic properties for the widget:
   *   - #field_parents: The 'parents' space for the field in the form. Most
   *       widgets can simply overlook this property. This identifies the
   *       location where the field values are placed within
   *       $form_state->getValues(), and is used to access processing
   *       information for the field through the getWidgetState() and
   *       setWidgetState() methods.
   *   - #title: The sanitized element label for the field, ready for output.
   *   - #description: The sanitized element description for the field, ready
   *     for output.
   *   - #required: A Boolean indicating whether the element value is required;
   *     for required multiple value fields, only the first widget's values are
   *     required.
   *   - #delta: The order of this item in the array of sub-elements; see $delta
   *     above.
   * @param array $form
   *   The form structure where widgets are being 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 current state of the form.
   *
   * @return array
   *   The form elements for a single widget for this field.
   *
   * @see hook_field_widget_single_element_form_alter()
   * @see hook_field_widget_single_element_WIDGET_TYPE_form_alter()
   */
  public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state);

  /**
   * Assigns a field-level validation error to the right widget sub-element.
   *
   * Depending on the widget's internal structure, a field-level validation
   * error needs to be flagged on the right sub-element.
   *
   * @param array $element
   *   An array containing the form element for the widget, as generated by
   *   formElement().
   * @param \Symfony\Component\Validator\ConstraintViolationInterface $violation
   *   A constraint violation reported during the validation phase.
   * @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 current state of the form.
   *
   * @return array|bool
   *   The element on which the error should be flagged, or FALSE to completely
   *   ignore the violation (use with care!).
   */
  public function errorElement(array $element, ConstraintViolationInterface $violation, array $form, FormStateInterface $form_state);

  /**
   * Massages the form values into the format expected for field values.
   *
   * @param array $values
   *   The submitted form values produced by the widget.
   *   - If the widget does not manage multiple values itself, the array holds
   *     the values generated by the multiple copies of the $element generated
   *     by the formElement() method, keyed by delta.
   *   - If the widget manages multiple values, the array holds the values
   *     of the form element generated by the formElement() method.
   * @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 of field values, keyed by delta.
   */
  public function massageFormValues(array $values, array $form, FormStateInterface $form_state);

  /**
   * Returns if the widget can be used for the provided field.
   *
   * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
   *   The field definition that should be checked.
   *
   * @return bool
   *   TRUE if the widget can be used, FALSE otherwise.
   */
  public static function isApplicable(FieldDefinitionInterface $field_definition);

}