class ContentEntity

class ContentEntity extends SourcePluginBase implements ContainerFactoryPluginInterface {
    use EntityFieldDefinitionTrait;
    
    /**
     * The entity type manager.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    protected $entityTypeManager;
    
    /**
     * The entity field manager.
     *
     * @var \Drupal\Core\Entity\EntityFieldManagerInterface
     */
    protected $entityFieldManager;
    
    /**
     * The entity type bundle info service.
     *
     * @var \Drupal\Core\Entity\EntityTypeBundleInfoInterface
     */
    protected $entityTypeBundleInfo;
    
    /**
     * The entity type definition.
     *
     * @var \Drupal\Core\Entity\EntityTypeInterface
     */
    protected $entityType;
    
    /**
     * The plugin's default configuration.
     *
     * @var array
     */
    protected $defaultConfiguration = [
        'bundle' => NULL,
        'include_translations' => TRUE,
        'add_revision_id' => TRUE,
    ];
    
    /**
     * {@inheritdoc}
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration, EntityTypeManagerInterface $entity_type_manager, EntityFieldManagerInterface $entity_field_manager, EntityTypeBundleInfoInterface $entity_type_bundle_info) {
        if (empty($plugin_definition['entity_type'])) {
            throw new InvalidPluginDefinitionException($plugin_id, 'Missing required "entity_type" definition.');
        }
        $this->entityTypeManager = $entity_type_manager;
        $this->entityFieldManager = $entity_field_manager;
        $this->entityTypeBundleInfo = $entity_type_bundle_info;
        $this->entityType = $this->entityTypeManager
            ->getDefinition($plugin_definition['entity_type']);
        if (!$this->entityType instanceof ContentEntityTypeInterface) {
            throw new InvalidPluginDefinitionException($plugin_id, sprintf('The entity type (%s) is not supported. The "content_entity" source plugin only supports content entities.', $plugin_definition['entity_type']));
        }
        if (!empty($configuration['bundle'])) {
            if (!$this->entityType
                ->hasKey('bundle')) {
                throw new \InvalidArgumentException(sprintf('A bundle was provided but the entity type (%s) is not bundleable.', $plugin_definition['entity_type']));
            }
            $bundle_info = array_keys($this->entityTypeBundleInfo
                ->getBundleInfo($this->entityType
                ->id()));
            if (!in_array($configuration['bundle'], $bundle_info, TRUE)) {
                throw new \InvalidArgumentException(sprintf('The provided bundle (%s) is not valid for the (%s) entity type.', $configuration['bundle'], $plugin_definition['entity_type']));
            }
        }
        parent::__construct($configuration + $this->defaultConfiguration, $plugin_id, $plugin_definition, $migration);
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration = NULL) {
        return new static($configuration, $plugin_id, $plugin_definition, $migration, $container->get('entity_type.manager'), $container->get('entity_field.manager'), $container->get('entity_type.bundle.info'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function __toString() {
        return (string) $this->entityType
            ->getPluralLabel();
    }
    
    /**
     * Initializes the iterator with the source data.
     *
     * @return \Generator
     *   A data generator for this source.
     */
    protected function initializeIterator() {
        $ids = $this->query()
            ->execute();
        return $this->yieldEntities($ids);
    }
    
    /**
     * Loads and yields entities, one at a time.
     *
     * @param array $ids
     *   The entity IDs.
     *
     * @return \Generator
     *   An iterable of the loaded entities.
     */
    protected function yieldEntities(array $ids) {
        $storage = $this->entityTypeManager
            ->getStorage($this->entityType
            ->id());
        foreach ($ids as $id) {
            
            /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
            $entity = $storage->load($id);
            (yield $this->toArray($entity));
            if ($this->configuration['include_translations']) {
                foreach ($entity->getTranslationLanguages(FALSE) as $language) {
                    (yield $this->toArray($entity->getTranslation($language->getId())));
                }
            }
        }
    }
    
    /**
     * Converts an entity to an array.
     *
     * Makes all IDs into flat values. All other values are returned as per
     * $entity->toArray(), which is a nested array.
     *
     * @param \Drupal\Core\Entity\ContentEntityInterface $entity
     *   The entity to convert.
     *
     * @return array
     *   The entity, represented as an array.
     */
    protected function toArray(ContentEntityInterface $entity) {
        $return = $entity->toArray();
        // This is necessary because the IDs must be flat. They cannot be nested for
        // the ID map.
        foreach (array_keys($this->getIds()) as $id) {
            
            /** @var \Drupal\Core\TypedData\Plugin\DataType\ItemList $value */
            $value = $entity->get($id);
            // Force the IDs on top of the previous values.
            $return[$id] = $value->first()
                ->getString();
        }
        return $return;
    }
    
    /**
     * Query to retrieve the entities.
     *
     * @return \Drupal\Core\Entity\Query\QueryInterface
     *   The query.
     */
    public function query() {
        $query = $this->entityTypeManager
            ->getStorage($this->entityType
            ->id())
            ->getQuery()
            ->accessCheck(FALSE);
        if (!empty($this->configuration['bundle'])) {
            $query->condition($this->entityType
                ->getKey('bundle'), $this->configuration['bundle']);
        }
        // Exclude anonymous user account.
        if ($this->entityType
            ->id() === 'user' && !empty($this->entityType
            ->getKey('id'))) {
            $query->condition($this->entityType
                ->getKey('id'), 0, '>');
        }
        return $query;
    }
    
    /**
     * {@inheritdoc}
     */
    public function count($refresh = FALSE) {
        // If no translations are included, then a simple query is possible.
        if (!$this->configuration['include_translations']) {
            return parent::count($refresh);
        }
        // @TODO: Determine a better way to retrieve a valid count for translations.
        // https://www.drupal.org/project/drupal/issues/2937166
        return MigrateSourceInterface::NOT_COUNTABLE;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function doCount() {
        return $this->query()
            ->count()
            ->execute();
    }
    
    /**
     * {@inheritdoc}
     */
    public function fields() {
        // Retrieving fields from a non-fieldable content entity will throw a
        // LogicException. Return an empty list of fields instead.
        if (!$this->entityType
            ->entityClassImplements('Drupal\\Core\\Entity\\FieldableEntityInterface')) {
            return [];
        }
        $field_definitions = $this->entityFieldManager
            ->getBaseFieldDefinitions($this->entityType
            ->id());
        if (!empty($this->configuration['bundle'])) {
            $field_definitions += $this->entityFieldManager
                ->getFieldDefinitions($this->entityType
                ->id(), $this->configuration['bundle']);
        }
        $fields = array_map(function ($definition) {
            return (string) $definition->getLabel();
        }, $field_definitions);
        return $fields;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getIds() {
        $id_key = $this->entityType
            ->getKey('id');
        $ids[$id_key] = $this->getDefinitionFromEntity($id_key);
        if ($this->configuration['add_revision_id'] && $this->entityType
            ->isRevisionable()) {
            $revision_key = $this->entityType
                ->getKey('revision');
            $ids[$revision_key] = $this->getDefinitionFromEntity($revision_key);
        }
        if ($this->entityType
            ->isTranslatable()) {
            $langcode_key = $this->entityType
                ->getKey('langcode');
            $ids[$langcode_key] = $this->getDefinitionFromEntity($langcode_key);
        }
        return $ids;
    }

}