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\RevisionableStorageInterface $storage */
            $storage = $this->entityTypeManager
                ->getStorage($entity->getEntityTypeId());
            
            /** @var \Drupal\Core\Entity\ContentEntityInterface $original_entity */
            $original_entity = $storage->loadRevision($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;
    }

}