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);
  }

}