class ModerationStateWidget

class ModerationStateWidget extends OptionsSelectWidget {
  
  /**
   * Current user service.
   *
   * @var \Drupal\Core\Session\AccountInterface
   */
  protected $currentUser;
  
  /**
   * Moderation information service.
   *
   * @var \Drupal\content_moderation\ModerationInformation
   */
  protected $moderationInformation;
  
  /**
   * The entity type manager.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;
  
  /**
   * Moderation state transition validation service.
   *
   * @var \Drupal\content_moderation\StateTransitionValidationInterface
   */
  protected $validator;
  
  /**
   * Constructs a new ModerationStateWidget object.
   *
   * @param string $plugin_id
   *   Plugin id.
   * @param mixed $plugin_definition
   *   Plugin definition.
   * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
   *   Field definition.
   * @param array $settings
   *   Field settings.
   * @param array $third_party_settings
   *   Third party settings.
   * @param \Drupal\Core\Session\AccountInterface $current_user
   *   Current user service.
   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *   Entity type manager.
   * @param \Drupal\content_moderation\ModerationInformation $moderation_information
   *   Moderation information service.
   * @param \Drupal\content_moderation\StateTransitionValidationInterface $validator
   *   Moderation state transition validation service.
   */
  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, array $third_party_settings, AccountInterface $current_user, EntityTypeManagerInterface $entity_type_manager, ModerationInformation $moderation_information, StateTransitionValidationInterface $validator) {
    parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $third_party_settings);
    $this->entityTypeManager = $entity_type_manager;
    $this->currentUser = $current_user;
    $this->moderationInformation = $moderation_information;
    $this->validator = $validator;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static($plugin_id, $plugin_definition, $configuration['field_definition'], $configuration['settings'], $configuration['third_party_settings'], $container->get('current_user'), $container->get('entity_type.manager'), $container->get('content_moderation.moderation_information'), $container->get('content_moderation.state_transition_validation'));
  }
  
  /**
   * {@inheritdoc}
   */
  public function form(FieldItemListInterface $items, array &$form, FormStateInterface $form_state, $get_delta = NULL) {
    $entity = $items->getEntity();
    if (!$this->moderationInformation
      ->isModeratedEntity($entity)) {
      return [];
    }
    return parent::form($items, $form, $form_state, $get_delta);
  }
  
  /**
   * {@inheritdoc}
   */
  public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
    /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
    $entity = $original_entity = $items->getEntity();
    $default = $this->moderationInformation
      ->getOriginalState($entity);
    // If the entity already exists, grab the most recent revision and load it.
    // The moderation state of the saved revision will be used to display the
    // current state as well determine the appropriate transitions.
    if (!$entity->isNew()) {
      /** @var \Drupal\Core\Entity\ContentEntityInterface $original_entity */
      $original_entity = $this->entityTypeManager
        ->getStorage($entity->getEntityTypeId())
        ->loadRevision($entity->getLoadedRevisionId());
      if (!$entity->isDefaultTranslation() && $original_entity->hasTranslation($entity->language()
        ->getId())) {
        $original_entity = $original_entity->getTranslation($entity->language()
          ->getId());
      }
    }
    else {
      $original_entity->set('moderation_state', $default->id());
    }
    /** @var \Drupal\workflows\Transition[] $transitions */
    $transitions = $this->validator
      ->getValidTransitions($original_entity, $this->currentUser);
    $transition_labels = [];
    $default_value = $items->value;
    foreach ($transitions as $transition) {
      $transition_to_state = $transition->to();
      $transition_labels[$transition_to_state->id()] = $transition_to_state->label();
      if ($default->id() === $transition_to_state->id()) {
        $default_value = $default->id();
      }
    }
    $element += [
      '#type' => 'container',
      'current' => [
        '#type' => 'item',
        '#title' => $this->t('Current state'),
        '#markup' => $default->label(),
        '#access' => !$entity->isNew(),
        '#wrapper_attributes' => [
          'class' => [
            'container-inline',
          ],
        ],
      ],
      'state' => [
        '#type' => 'select',
        '#title' => $entity->isNew() ? $this->t('Save as') : $this->t('Change to'),
        '#key_column' => $this->column,
        '#options' => $transition_labels,
        '#default_value' => $default_value,
        '#access' => !empty($transition_labels),
        '#wrapper_attributes' => [
          'class' => [
            'container-inline',
          ],
        ],
      ],
    ];
    $element['#element_validate'][] = [
      static::class,
      'validateElement',
    ];
    return $element;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function validateElement(array $element, FormStateInterface $form_state) {
    $form_state->setValueForElement($element, [
      $element['state']['#key_column'] => $element['state']['#value'],
    ]);
  }
  
  /**
   * {@inheritdoc}
   */
  public static function isApplicable(FieldDefinitionInterface $field_definition) {
    return is_a($field_definition->getClass(), ModerationStateFieldItemList::class, TRUE);
  }
  
  /**
   * {@inheritdoc}
   */
  public function calculateDependencies() {
    $dependencies = parent::calculateDependencies();
    if ($workflow = $this->moderationInformation
      ->getWorkflowForEntityTypeAndBundle($this->fieldDefinition
      ->getTargetEntityTypeId(), $this->fieldDefinition
      ->getTargetBundle())) {
      $dependencies[$workflow->getConfigDependencyKey()][] = $workflow->getConfigDependencyName();
    }
    return $dependencies;
  }

}