abstract class Entity

abstract class Entity extends DestinationBase implements ContainerFactoryPluginInterface, DependentPluginInterface {
  use DependencyTrait;
  use EntityFieldDefinitionTrait;

  /**
   * The entity storage.
   *
   * @var \Drupal\Core\Entity\EntityStorageInterface
   */
  protected $storage;

  /**
   * The list of the bundles of this entity type.
   *
   * @var array
   */
  protected $bundles;

  /**
   * Construct a new entity.
   *
   * @param array $configuration
   *   A configuration array containing information about the plugin instance.
   * @param string $plugin_id
   *   The plugin_id for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Drupal\migrate\Plugin\MigrationInterface $migration
   *   The migration.
   * @param \Drupal\Core\Entity\EntityStorageInterface $storage
   *   The storage for this entity type.
   * @param array $bundles
   *   The list of bundles this entity type has.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration, EntityStorageInterface $storage, array $bundles) {
    $plugin_definition += [
      'label' => $storage
        ->getEntityType()
        ->getPluralLabel(),
    ];
    parent::__construct($configuration, $plugin_id, $plugin_definition, $migration);
    $this->storage = $storage;
    $this->bundles = $bundles;
    $this->supportsRollback = TRUE;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration = NULL) {
    $entity_type_id = static::getEntityTypeId($plugin_id);
    return new static($configuration, $plugin_id, $plugin_definition, $migration, $container
      ->get('entity_type.manager')
      ->getStorage($entity_type_id), array_keys($container
      ->get('entity_type.bundle.info')
      ->getBundleInfo($entity_type_id)));
  }

  /**
   * Gets the bundle for the row taking into account the default.
   *
   * @param \Drupal\migrate\Row $row
   *   The current row we're importing.
   *
   * @return string
   *   The bundle for this row.
   */
  public function getBundle(Row $row) {
    $default_bundle = isset($this->configuration['default_bundle']) ? $this->configuration['default_bundle'] : '';
    $bundle_key = $this
      ->getKey('bundle');
    return $row
      ->getDestinationProperty($bundle_key) ?: $default_bundle;
  }

  /**
   * {@inheritdoc}
   */
  public function fields(MigrationInterface $migration = NULL) {

    // TODO: Implement fields() method.
  }

  /**
   * Creates or loads an entity.
   *
   * @param \Drupal\migrate\Row $row
   *   The row object.
   * @param array $old_destination_id_values
   *   The old destination IDs.
   *
   * @return \Drupal\Core\Entity\EntityInterface
   *   The entity we are importing into.
   */
  protected function getEntity(Row $row, array $old_destination_id_values) {
    $entity_id = reset($old_destination_id_values) ?: $this
      ->getEntityId($row);
    if (!empty($entity_id) && ($entity = $this->storage
      ->load($entity_id))) {

      // Allow updateEntity() to change the entity.
      $entity = $this
        ->updateEntity($entity, $row) ?: $entity;
    }
    else {

      // Attempt to ensure we always have a bundle.
      if ($bundle = $this
        ->getBundle($row)) {
        $row
          ->setDestinationProperty($this
          ->getKey('bundle'), $bundle);
      }

      // Stubs might need some required fields filled in.
      if ($row
        ->isStub()) {
        $this
          ->processStubRow($row);
      }
      $entity = $this->storage
        ->create($row
        ->getDestination());
      $entity
        ->enforceIsNew();
    }
    return $entity;
  }

  /**
   * Gets the entity ID of the row.
   *
   * @param \Drupal\migrate\Row $row
   *   The row of data.
   *
   * @return string
   *   The entity ID for the row that we are importing.
   */
  protected function getEntityId(Row $row) {
    return $row
      ->getDestinationProperty($this
      ->getKey('id'));
  }

  /**
   * Returns a specific entity key.
   *
   * @param string $key
   *   The name of the entity key to return.
   *
   * @return string|bool
   *   The entity key, or FALSE if it does not exist.
   *
   * @see \Drupal\Core\Entity\EntityTypeInterface::getKeys()
   */
  protected function getKey($key) {
    return $this->storage
      ->getEntityType()
      ->getKey($key);
  }

  /**
   * {@inheritdoc}
   */
  public function rollback(array $destination_identifier) {

    // Delete the specified entity from Drupal if it exists.
    $entity = $this->storage
      ->load(reset($destination_identifier));
    if ($entity) {
      $entity
        ->delete();
    }
  }

  /**
   * {@inheritdoc}
   */
  public function calculateDependencies() {
    $this
      ->addDependency('module', $this->storage
      ->getEntityType()
      ->getProvider());
    return $this->dependencies;
  }

}