abstract class CustomCSVImportPluginBase extends PluginBase implements CustomCSVImportPluginInterface, ContainerFactoryPluginInterface {

  /**
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;

  /**
   * @var \Drupal\Core\File\FileSystemInterface
   */
  protected $fileSystem;

  /**
   * {@inheritdoc}
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, EntityTypeManagerInterface $entity_type_manager = NULL, FileSystemInterface $file_system = NULL) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);

    $this->entityTypeManager = $entity_type_manager;
    $this->fileSystem = $file_system;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static(
      $configuration,
      $plugin_id,
      $plugin_definition,
      $container->get('entity_type.manager'),
      $container->get('file_system')
    );
  }

/**
   * Load for edit or create new entity by unique id from CSV.
   *
   * @param $id
   *   Unique ID in CSV file.
   * @param $entity_type
   *   The entity type id.
   * @param $bundle
   *   The bundle of entity type.
   * @param $field_id
   *   Proxy field`s name of unique id from CSV for edit.
   *
   * @return \Drupal\Core\Entity\EntityInterface|null
   *
   * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
   * @throws \Drupal\Component\Plugin\Exception\PluginNotFoundException
   */
  protected function getContentEntityByUid($id, $entity_type, $bundle, $field_id) {
    $storage = $this->entityTypeManager->getStorage($entity_type);
    $bundle_name = $this->getContentBundleName();

    $eid = $storage->getQuery()
      ->condition($bundle_name, $bundle)
      ->condition($field_id, $id)
      ->execute();

    if (!empty($eid)) {
      $entity = $storage->load($eid[key($eid)]);
    }
    else {
      $entity = $storage->create([
        $bundle_name => $bundle,
        'langcode' => 'en',
        'uid' => 1,
        'status' => 1,
      ]);

      $entity->set($field_id, $id);
    }

    return $entity;
  }