class TextItemBase

abstract class TextItemBase extends FieldItemBase {
  
  /**
   * {@inheritdoc}
   */
  public static function defaultFieldSettings() {
    return [
      'allowed_formats' => [],
    ] + parent::defaultFieldSettings();
  }
  
  /**
   * {@inheritdoc}
   */
  public function fieldSettingsForm(array $form, FormStateInterface $form_state) {
    $element = parent::fieldSettingsForm($form, $form_state);
    $settings = $this->getSettings();
    $element['allowed_formats'] = [
      '#type' => 'checkboxes',
      '#title' => $this->t('Allowed text formats'),
      '#options' => $this->get('format')
        ->getPossibleOptions(),
      '#default_value' => !empty($settings['allowed_formats']) ? $settings['allowed_formats'] : [],
      '#description' => $this->t('Select the allowed text formats. If no formats are selected, all available text formats will be displayed to the user.'),
      '#element_validate' => [
        [
          static::class,
          'validateAllowedFormats',
        ],
      ],
    ];
    return $element;
  }
  
  /**
   * Render API callback: Processes the allowed formats value.
   *
   * Ensure the element's value is an indexed array of selected format IDs.
   * This function is assigned as an #element_validate callback.
   *
   * @see static::fieldSettingsForm()
   */
  public static function validateAllowedFormats(array &$element, FormStateInterface $form_state) {
    $value = array_values(array_filter($form_state->getValue($element['#parents'])));
    $form_state->setValueForElement($element, $value);
  }
  
  /**
   * {@inheritdoc}
   */
  public static function calculateDependencies(FieldDefinitionInterface $field_definition) {
    // Add explicitly allowed formats as config dependencies.
    $format_dependencies = [];
    $dependencies = parent::calculateDependencies($field_definition);
    if (!is_null($field_definition->getSetting('allowed_formats'))) {
      $format_dependencies = array_map(function (string $format_id) {
        return 'filter.format.' . $format_id;
      }, $field_definition->getSetting('allowed_formats'));
    }
    $config = $dependencies['config'] ?? [];
    $dependencies['config'] = array_merge($config, $format_dependencies);
    return $dependencies;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
    $properties['value'] = DataDefinition::create('string')->setLabel(t('Text'))
      ->setRequired(TRUE);
    $properties['format'] = DataDefinition::create('filter_format')->setLabel(t('Text format'))
      ->setSetting('allowed_formats', $field_definition->getSetting('allowed_formats'));
    $properties['processed'] = DataDefinition::create('string')->setLabel(t('Processed text'))
      ->setDescription(t('The text with the text format applied.'))
      ->setComputed(TRUE)
      ->setClass('\\Drupal\\text\\TextProcessed')
      ->setSetting('text source', 'value')
      ->setInternal(FALSE);
    return $properties;
  }
  
  /**
   * {@inheritdoc}
   */
  public function applyDefaultValue($notify = TRUE) {
    // @todo Add in the filter default format here.
    $this->setValue([
      'format' => NULL,
    ], $notify);
    return $this;
  }
  
  /**
   * {@inheritdoc}
   */
  public function isEmpty() {
    $value = $this->get('value')
      ->getValue();
    return $value === NULL || $value === '';
  }
  
  /**
   * {@inheritdoc}
   */
  public function onChange($property_name, $notify = TRUE) {
    // Unset processed properties that are affected by the change.
    foreach ($this->definition
      ->getPropertyDefinitions() as $property => $definition) {
      if ($definition->getClass() == '\\Drupal\\text\\TextProcessed') {
        if ($property_name == 'format' || $definition->getSetting('text source') == $property_name) {
          $this->writePropertyValue($property, NULL);
        }
      }
    }
    parent::onChange($property_name, $notify);
  }
  
  /**
   * {@inheritdoc}
   */
  public static function generateSampleValue(FieldDefinitionInterface $field_definition) {
    $random = new Random();
    $settings = $field_definition->getSettings();
    if (empty($settings['max_length'])) {
      // Textarea handling.
      $value = $random->paragraphs(2);
    }
    else {
      // Textfield handling.
      $max = (int) ceil($settings['max_length'] / 3);
      $value = substr($random->sentences(mt_rand(1, $max), FALSE), 0, $settings['max_length']);
    }
    $values = [
      'value' => $value,
      'summary' => $value,
      'format' => \Drupal::service(FilterFormatRepositoryInterface::class)->getFallbackFormatId(),
    ];
    return $values;
  }

}