trait ViewsReferenceTrait in Views Reference Field 8.2

trait ViewsReferenceTrait {

  /**
   * Build a field element for a viewsreference field.
   *
   * @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
   *   The field item element.
   * @param array $form
   *   The overall form array.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   Array of default values for this field.
   *
   * @return array
   *   The changed field element.
   */
  public function fieldElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
    $field_name = $this->fieldDefinition
      ->getName();

    // Determine the element parents.
    $field_parents = [];
    if (isset($element['#field_parents'])) {
      $field_parents = $element['#field_parents'];
    }
    elseif (isset($element['target_id']['#field_parents'])) {
      $field_parents = $element['target_id']['#field_parents'];
    }
    $field_path = array_merge($field_parents, [
      $field_name,
      $delta,
    ]);
    $target_id_field_path = array_merge($field_path, [
      'target_id',
    ]);

    // Get the current values.
    $field_value = $this
      ->itemCurrentValues($items, $delta, $element, $form, $form_state);

    // Setup JavaScript states.
    switch ($element['target_id']['#type']) {
      case 'select':
        $view_selected_js_state = [
          '!value' => '_none',
        ];
        $ajax_event = 'change';
        $element['target_id']['#default_value'] = isset($field_value['target_id']) ? $field_value['target_id'] : '';
        break;
      default:
        $view_selected_js_state = [
          'filled' => TRUE,
        ];
        $ajax_event = 'viewsreference-select';
        break;
    }

    // Build our target_id field name attribute from the parent elements.
    $target_id_names = $target_id_field_path;
    $target_id_name_string = array_shift($target_id_names);
    foreach ($target_id_names as $target_id_name) {
      $target_id_name_string .= '[' . $target_id_name . ']';
    }

    // We build a unique class name from field elements and any parent elements
    // that might exist which will be used to render the display id options in
    // our ajax function.
    $html_wrapper_id = Html::getUniqueId(implode('-', $field_path));
    $class = get_class($this);
    $element['target_id']['#target_type'] = 'view';
    $element['target_id']['#limit_validation_errors'] = [];
    $element['target_id']['#ajax'] = [
      'callback' => [
        $class,
        'itemAjaxRefresh',
      ],
      'event' => $ajax_event,
      'wrapper' => $html_wrapper_id,
      'progress' => [
        'type' => 'throbber',
        'message' => $this
          ->t('Getting display IDs...'),
      ],
    ];
    $display_id = $field_value['display_id'] ?? NULL;
    $view_name = $field_value['target_id'] ?? NULL;
    $options = [];
    if ($view_name) {

      // Extract the view id from the text.
      preg_match('#\\((.*?)\\)#', $view_name, $match);
      if (!empty($match)) {
        $view_name = $match[1];
      }
      $options = $this
        ->getViewDisplays($view_name);
    }
    $element['display_id'] = [
      '#title' => $this
        ->t('Display'),
      '#type' => 'select',
      '#options' => $options,
      '#default_value' => $display_id,
      '#empty_option' => $this
        ->t('- Select -'),
      '#empty_value' => '',
      '#weight' => 10,
      '#attributes' => [
        'class' => [
          'viewsreference-display-id',
        ],
      ],
      '#states' => [
        'visible' => [
          ':input[name="' . $target_id_name_string . '"]' => $view_selected_js_state,
        ],
        'required' => [
          ':input[name="' . $target_id_name_string . '"]' => $view_selected_js_state,
        ],
      ],
      '#ajax' => [
        'callback' => [
          $class,
          'itemAjaxRefresh',
        ],
        'event' => $ajax_event,
        'wrapper' => $html_wrapper_id,
        'progress' => [
          'type' => 'throbber',
          'message' => $this
            ->t('Getting options...'),
        ],
      ],
    ];
    $field_data = [];
    if (isset($field_value['data'])) {
      $field_data = unserialize($field_value['data'], [
        'allowed_classes' => FALSE,
      ]);
    }
    $element['options'] = [
      '#type' => 'details',
      '#title' => $this
        ->t('Options'),
      '#weight' => 10,
      '#states' => [
        'visible' => [
          ':input[name="' . $target_id_name_string . '"]' => $view_selected_js_state,
        ],
      ],
    ];
    $viewsreference_plugin_manager = \Drupal::service('plugin.manager.viewsreference.setting');
    $plugin_definitions = $viewsreference_plugin_manager
      ->getDefinitions();
    $enabled_settings = array_filter($this
      ->getFieldSetting('enabled_settings') ?? []);
    foreach ($enabled_settings as $enabled_setting) {
      if (!empty($plugin_definitions[$enabled_setting])) {
        $plugin_definition = $plugin_definitions[$enabled_setting];

        /** @var \Drupal\viewsreference\Plugin\ViewsReferenceSettingInterface $plugin_instance */
        $plugin_instance = $viewsreference_plugin_manager
          ->createInstance($plugin_definition['id'], [
          'view_name' => $view_name,
          'display_id' => $display_id,
        ]);
        $element['options'][$plugin_definition['id']] = [
          '#title' => $plugin_definition['label'],
          '#type' => 'textfield',
          '#default_value' => $field_data[$plugin_definition['id']] ?? $plugin_definition['default_value'],
          '#states' => [
            'visible' => [
              ':input[name="' . $target_id_name_string . '"]' => $view_selected_js_state,
            ],
          ],
        ];
        $plugin_instance
          ->alterFormField($element['options'][$plugin_definition['id']]);
      }
    }
    if (empty($enabled_settings)) {
      unset($element['options']);
    }
    $element['#attached']['library'][] = 'viewsreference/viewsreference';
    $element['#after_build'][] = [
      $class,
      'itemResetValues',
    ];

    // Wrap element for AJAX replacement.
    $element = [
      '#prefix' => '<div id="' . $html_wrapper_id . '">',
      '#suffix' => '</div>',
      // Pass the id along to other methods.
      '#wrapper_id' => $html_wrapper_id,
    ] + $element;
    return $element;
  }

  /**
   * Build a field element for a viewsreference field.
   *
   * @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
   *   The field item element.
   * @param array $form
   *   The overall form array.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   Array of default values for this field.
   *
   * @return array
   *   The changed field element.
   */
  public function itemCurrentValues(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
    $values = [];
    $field_name = $this->fieldDefinition
      ->getName();
    $value_parents = [];
    if (isset($element['#field_parents'])) {
      $value_parents = $element['#field_parents'];
    }
    elseif (isset($element['target_id']['#field_parents'])) {
      $value_parents = $element['target_id']['#field_parents'];
    }
    $value_parents = array_merge($value_parents, [
      $field_name,
      $delta,
    ]);

    // Get the current value.
    $form_input_values = $form_state
      ->getUserInput();
    $input_value_exists = NULL;
    if ($form_input_values) {

      // User input.
      $input_values = NestedArray::getValue($form_input_values, $value_parents, $input_value_exists);
      if ($input_value_exists) {
        $values = $input_values;
      }
    }
    if (!$input_value_exists) {
      if ($item_state_values = $form_state
        ->getValue($value_parents)) {

        // Stored form state.
        $values = $item_state_values;
      }
      elseif ($item_values = $items[$delta]
        ->getValue()) {

        // Saved items values.
        $values = $item_values;
      }
    }
    return $values;
  }

  /**
   * Clears dependent form values when the view id changes.
   *
   * Implemented as an #after_build callback because #after_build runs before
   * validation, allowing the values to be cleared early enough to prevent the
   * "Illegal choice" error.
   */
  public static function itemResetValues(array $element, FormStateInterface $form_state) {
    $triggering_element = $form_state
      ->getTriggeringElement();
    if (!$triggering_element) {
      return $element;
    }
    $keys = [
      'target_id' => [
        'display_id',
      ],
    ];
    $triggering_element_name = end($triggering_element['#parents']);
    if (isset($keys[$triggering_element_name])) {
      $input =& $form_state
        ->getUserInput();
      foreach ($keys[$triggering_element_name] as $key) {
        $parents = array_merge($element['#parents'], [
          $key,
        ]);
        NestedArray::setValue($input, $parents, '');
        $element[$key]['#value'] = '';
      }
    }
    return $element;
  }

  /**
   * Ajax callback to refresh the widget.
   */
  public static function itemAjaxRefresh(array $form, FormStateInterface $form_state) {
    $triggering_element = $form_state
      ->getTriggeringElement();
    $parents = $triggering_element['#array_parents'];
    array_pop($parents);
    return NestedArray::getValue($form, $parents);
  }

  /**
   * Helper function to get all display ids.
   */
  protected function getAllViewsDisplayIds() {
    $views = Views::getAllViews();
    $options = [];
    foreach ($views as $view) {
      if ($displays = $view
        ->get('display')) {
        foreach ($displays as $display) {
          $options[$display['id']] = $display['display_title'];
        }
      }
    }
    return $options;
  }

  /**
   * Get displays for a particular view.
   *
   * @param string $view_id
   *   The view ID.
   *
   * @return array
   *   An array containing displays for the view.
   */
  protected function getViewDisplays($view_id) {
    $options = [];
    $view_plugins = array_diff($this
      ->getFieldSetting('plugin_types'), [
      '0',
    ]);

    /** @var \Drupal\views\Entity\View $view */
    if ($view = \Drupal::service('entity_type.manager')
      ->getStorage('view')
      ->load($view_id)) {
      if ($displays = $view
        ->get('display')) {
        usort($displays, function ($a, $b) {
          return $a['position'] <=> $b['position'];
        });
        foreach ($displays as $display) {
          if (in_array($display['display_plugin'], $view_plugins, TRUE)) {
            $options[$display['id']] = $display['display_title'];
          }
        }
      }
    }
    return $options;
  }

  /**
   * Get view names for a list of view machine names.
   *
   * @param array $views_array
   *   An array containing view machine names.
   *
   * @return array
   *   An array with view labels keyed by machine name.
   */
  protected function getViewNames(array $views_array) {
    $views_list = [];
    foreach ($views_array as $key => $value) {
      if ($view = Views::getView($key)) {
        $views_list[$view->storage
          ->id()] = $view->storage
          ->label();
      }
    }
    return $views_list;
  }

  /**
   * Massages the form values into the format expected for field values.
   *
   * We need to flatten the options array and serialize the settings for the
   * data attribute.
   *
   * @param array $values
   *   The submitted form values produced by the widget.
   * @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) {
    $values = parent::massageFormValues($values, $form, $form_state);
    foreach ($values as $key => $value) {
      if (isset($value['options']) && is_array($value['options'])) {
        foreach ($value['options'] as $ind => $option) {
          $values[$key][$ind] = $option;
        }
        unset($value['options']);
      }
    }

    // Serialize settings to store them in the data attribute.
    $values = $this
      ->serializeSettingsValues($values);
    return $values;
  }

  /**
   * Serialize views reference settings for storage in the data attribute.
   *
   * @param array $values
   *   The submitted form values produced by the widget.
   *
   * @return array
   *   The changed values with a serialized data attribute.
   */
  protected function serializeSettingsValues(array $values) {
    $viewsreference_plugin_manager = \Drupal::service('plugin.manager.viewsreference.setting');
    $plugin_definitions = $viewsreference_plugin_manager
      ->getDefinitions();
    foreach ($values as $delta => $value) {
      $serialized_fields = [];
      foreach ($plugin_definitions as $plugin_definition) {
        $serialized_fields[$plugin_definition['id']] = isset($value[$plugin_definition['id']]) ? $value[$plugin_definition['id']] : NULL;
        unset($values[$delta][$plugin_definition['id']]);
      }
      $values[$delta]['data'] = serialize($serialized_fields);
    }
    return $values;
  }

}