class VocabularyForm

class VocabularyForm extends BundleEntityFormBase {
    
    /**
     * The vocabulary storage.
     *
     * @var \Drupal\taxonomy\VocabularyStorageInterface
     */
    protected $vocabularyStorage;
    
    /**
     * Constructs a new vocabulary form.
     *
     * @param \Drupal\taxonomy\VocabularyStorageInterface $vocabulary_storage
     *   The vocabulary storage.
     */
    public function __construct(VocabularyStorageInterface $vocabulary_storage) {
        $this->vocabularyStorage = $vocabulary_storage;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity_type.manager')
            ->getStorage('taxonomy_vocabulary'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildEntity(array $form, FormStateInterface $form_state) {
        
        /** @var \Drupal\taxonomy\VocabularyInterface $entity */
        $entity = parent::buildEntity($form, $form_state);
        // The description cannot be an empty string.
        if (trim($form_state->getValue('description')) === '') {
            $entity->set('description', NULL);
        }
        return $entity;
    }
    
    /**
     * {@inheritdoc}
     */
    public function form(array $form, FormStateInterface $form_state) {
        $vocabulary = $this->entity;
        if ($vocabulary->isNew()) {
            $form['#title'] = $this->t('Add vocabulary');
        }
        else {
            $form['#title'] = $this->t('Edit vocabulary');
        }
        $form['name'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Name'),
            '#default_value' => $vocabulary->label(),
            '#maxlength' => 255,
            '#required' => TRUE,
        ];
        $form['vid'] = [
            '#type' => 'machine_name',
            '#default_value' => $vocabulary->id(),
            '#maxlength' => EntityTypeInterface::BUNDLE_MAX_LENGTH,
            '#machine_name' => [
                'exists' => [
                    $this,
                    'exists',
                ],
                'source' => [
                    'name',
                ],
            ],
        ];
        $form['description'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Description'),
            '#default_value' => $vocabulary->getDescription(),
        ];
        $form['revision'] = [
            '#type' => 'checkbox',
            '#title' => $this->t('Create new revision'),
            '#default_value' => $vocabulary->shouldCreateNewRevision(),
            '#description' => $this->t('Create a new revision by default for this vocabulary.'),
        ];
        // $form['langcode'] is not wrapped in an
        // if ($this->moduleHandler->moduleExists('language')) check because the
        // language_select form element works also without the language module being
        // installed. https://www.drupal.org/node/1749954 documents the new element.
        $form['langcode'] = [
            '#type' => 'language_select',
            '#title' => $this->t('Vocabulary language'),
            '#languages' => LanguageInterface::STATE_ALL,
            '#default_value' => $vocabulary->language()
                ->getId(),
        ];
        if ($this->moduleHandler
            ->moduleExists('language')) {
            $form['default_terms_language'] = [
                '#type' => 'details',
                '#title' => $this->t('Term language'),
                '#open' => TRUE,
            ];
            $form['default_terms_language']['default_language'] = [
                '#type' => 'language_configuration',
                '#entity_information' => [
                    'entity_type' => 'taxonomy_term',
                    'bundle' => $vocabulary->id(),
                ],
                '#default_value' => ContentLanguageSettings::loadByEntityTypeBundle('taxonomy_term', $vocabulary->id()),
            ];
        }
        // Set the hierarchy to "multiple parents" by default. This simplifies the
        // vocabulary form and standardizes the term form.
        $form['hierarchy'] = [
            '#type' => 'value',
            '#value' => '0',
        ];
        $form = parent::form($form, $form_state);
        return $this->protectBundleIdElement($form);
    }
    
    /**
     * {@inheritdoc}
     */
    public function save(array $form, FormStateInterface $form_state) {
        $vocabulary = $this->entity;
        $vocabulary->setNewRevision($form_state->getValue([
            'revision',
        ]));
        // Prevent leading and trailing spaces in vocabulary names.
        $vocabulary->set('name', trim($vocabulary->label()));
        $status = $vocabulary->save();
        $edit_link = $this->entity
            ->toLink($this->t('Edit'), 'edit-form')
            ->toString();
        switch ($status) {
            case SAVED_NEW:
                $this->messenger()
                    ->addStatus($this->t('Created new vocabulary %name.', [
                    '%name' => $vocabulary->label(),
                ]));
                $this->logger('taxonomy')
                    ->notice('Created new vocabulary %name.', [
                    '%name' => $vocabulary->label(),
                    'link' => $edit_link,
                ]);
                $form_state->setRedirectUrl($vocabulary->toUrl('overview-form'));
                break;
            case SAVED_UPDATED:
                $this->messenger()
                    ->addStatus($this->t('Updated vocabulary %name.', [
                    '%name' => $vocabulary->label(),
                ]));
                $this->logger('taxonomy')
                    ->notice('Updated vocabulary %name.', [
                    '%name' => $vocabulary->label(),
                    'link' => $edit_link,
                ]);
                $form_state->setRedirectUrl($vocabulary->toUrl('collection'));
                break;
        }
        $form_state->setValue('vid', $vocabulary->id());
        $form_state->set('vid', $vocabulary->id());
    }
    
    /**
     * Determines if the vocabulary already exists.
     *
     * @param string $vid
     *   The vocabulary ID.
     *
     * @return bool
     *   TRUE if the vocabulary exists, FALSE otherwise.
     */
    public function exists($vid) {
        $action = $this->vocabularyStorage
            ->load($vid);
        return !empty($action);
    }

}