abstract class FieldItemBase

abstract class FieldItemBase extends Map implements FieldItemInterface {

  /**
   * {@inheritdoc}
   */
  public static function defaultStorageSettings() {
    return [];
  }

  /**
   * {@inheritdoc}
   */
  public static function defaultFieldSettings() {
    return [];
  }

  /**
   * {@inheritdoc}
   */
  public static function storageSettingsSummary(FieldStorageDefinitionInterface $storage_definition) : array {
    return [];
  }

  /**
   * {@inheritdoc}
   */
  public static function fieldSettingsSummary(FieldDefinitionInterface $field_definition) : array {
    return [];
  }

  /**
   * {@inheritdoc}
   */
  public static function mainPropertyName() {
    return 'value';
  }

  /**
   * {@inheritdoc}
   */
  public function __construct(ComplexDataDefinitionInterface $definition, $name = NULL, TypedDataInterface $parent = NULL) {
    parent::__construct($definition, $name, $parent);

    // Initialize computed properties by default, such that they get cloned
    // with the whole item.
    foreach ($this->definition
      ->getPropertyDefinitions() as $name => $definition) {
      if ($definition
        ->isComputed()) {
        $this->properties[$name] = \Drupal::typedDataManager()
          ->getPropertyInstance($this, $name);
      }
    }
  }

  /**
   * {@inheritdoc}
   */
  public function getEntity() {
    return $this
      ->getParent()
      ->getEntity();
  }

  /**
   * {@inheritdoc}
   */
  public function getLangcode() {
    return $this
      ->getParent()
      ->getLangcode();
  }

  /**
   * {@inheritdoc}
   */
  public function getFieldDefinition() {
    return $this->definition
      ->getFieldDefinition();
  }

  /**
   * Returns the array of field settings.
   *
   * @return array
   *   The array of settings.
   */
  protected function getSettings() {
    return $this
      ->getFieldDefinition()
      ->getSettings();
  }

  /**
   * Returns the value of a field setting.
   *
   * @param string $setting_name
   *   The setting name.
   *
   * @return mixed
   *   The setting value.
   */
  protected function getSetting($setting_name) {
    return $this
      ->getFieldDefinition()
      ->getSetting($setting_name);
  }

  /**
   * {@inheritdoc}
   */
  public function setValue($values, $notify = TRUE) {

    // Treat the values as property value of the first property, if no array is
    // given.
    if (isset($values) && !is_array($values)) {
      $keys = array_keys($this->definition
        ->getPropertyDefinitions());
      $values = [
        $keys[0] => $values,
      ];
    }
    parent::setValue($values, $notify);
  }

  /**
   * {@inheritdoc}
   *
   * Different to the parent Map class, we avoid creating property objects as
   * far as possible in order to optimize performance. Thus we just update
   * $this->values if no property object has been created yet.
   */
  protected function writePropertyValue($property_name, $value) {

    // For defined properties there is either a property object or a plain
    // value that needs to be updated.
    if (isset($this->properties[$property_name])) {
      $this->properties[$property_name]
        ->setValue($value, FALSE);
    }
    else {
      $this->values[$property_name] = $value;
    }
  }

  /**
   * {@inheritdoc}
   */
  public function __get($name) {

    // There is either a property object or a plain value - possibly for a
    // not-defined property. If we have a plain value, directly return it.
    if (isset($this->properties[$name])) {
      return $this->properties[$name]
        ->getValue();
    }
    elseif (isset($this->values[$name])) {
      return $this->values[$name];
    }
  }

  /**
   * {@inheritdoc}
   */
  public function __set($name, $value) {

    // Support setting values via property objects, but take care in as the
    // value of the 'entity' property is typed data also.
    if ($value instanceof TypedDataInterface && !$value instanceof EntityInterface) {
      $value = $value
        ->getValue();
    }
    $this
      ->set($name, $value);
  }

  /**
   * {@inheritdoc}
   */
  public function __isset($name) {
    if (isset($this->properties[$name])) {
      return $this->properties[$name]
        ->getValue() !== NULL;
    }
    return isset($this->values[$name]);
  }

  /**
   * {@inheritdoc}
   */
  public function __unset($name) {
    if ($this->definition
      ->getPropertyDefinition($name)) {
      $this
        ->set($name, NULL);
    }
    else {

      // Explicitly unset the property in $this->values if a non-defined
      // property is unset, such that its key is removed from $this->values.
      unset($this->values[$name]);
    }
  }

  /**
   * {@inheritdoc}
   */
  public function view($display_options = []) {
    $view_builder = \Drupal::entityTypeManager()
      ->getViewBuilder($this
      ->getEntity()
      ->getEntityTypeId());
    return $view_builder
      ->viewFieldItem($this, $display_options);
  }

  /**
   * {@inheritdoc}
   */
  public function preSave() {
  }

  /**
   * {@inheritdoc}
   */
  public function postSave($update) {
  }

  /**
   * {@inheritdoc}
   */
  public function delete() {
  }

  /**
   * {@inheritdoc}
   */
  public static function generateSampleValue(FieldDefinitionInterface $field_definition) {
  }

  /**
   * {@inheritdoc}
   */
  public function deleteRevision() {
  }

  /**
   * {@inheritdoc}
   */
  public function storageSettingsForm(array &$form, FormStateInterface $form_state, $has_data) {
    return [];
  }

  /**
   * {@inheritdoc}
   */
  public function fieldSettingsForm(array $form, FormStateInterface $form_state) {
    return [];
  }

  /**
   * {@inheritdoc}
   */
  public static function storageSettingsToConfigData(array $settings) {
    return $settings;
  }

  /**
   * {@inheritdoc}
   */
  public static function storageSettingsFromConfigData(array $settings) {
    return $settings;
  }

  /**
   * {@inheritdoc}
   */
  public static function fieldSettingsToConfigData(array $settings) {
    return $settings;
  }

  /**
   * {@inheritdoc}
   */
  public static function fieldSettingsFromConfigData(array $settings) {
    return $settings;
  }

  /**
   * {@inheritdoc}
   */
  public static function calculateDependencies(FieldDefinitionInterface $field_definition) {
    return [];
  }

  /**
   * {@inheritdoc}
   */
  public static function calculateStorageDependencies(FieldStorageDefinitionInterface $field_definition) {
    return [];
  }

  /**
   * {@inheritdoc}
   */
  public static function onDependencyRemoval(FieldDefinitionInterface $field_definition, array $dependencies) {
    return FALSE;
  }

}