class EmbeddedDataSource

class EmbeddedDataSource extends SourcePluginBase {
    
    /**
     * Data obtained from the source plugin configuration.
     *
     * @var array[]
     *   Array of data rows, each one an array of values keyed by field names.
     */
    protected $dataRows = [];
    
    /**
     * Description of the unique ID fields for this source.
     *
     * @var array[]
     *   Each array member is keyed by a field name, with a value that is an
     *   array with a single member with key 'type' and value a column type such
     *   as 'integer'.
     */
    protected $ids = [];
    
    /**
     * {@inheritdoc}
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration) {
        parent::__construct($configuration, $plugin_id, $plugin_definition, $migration);
        $this->dataRows = $configuration['data_rows'];
        $this->ids = $configuration['ids'];
    }
    
    /**
     * {@inheritdoc}
     */
    public function fields() {
        if ($this->count() > 0) {
            $first_row = reset($this->dataRows);
            $field_names = array_keys($first_row);
            return array_combine($field_names, $field_names);
        }
        else {
            return [];
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function initializeIterator() {
        return new \ArrayIterator($this->dataRows);
    }
    
    /**
     * {@inheritdoc}
     */
    public function __toString() {
        return 'Embedded data';
    }
    
    /**
     * {@inheritdoc}
     */
    public function getIds() {
        return $this->ids;
    }
    
    /**
     * {@inheritdoc}
     */
    public function count($refresh = FALSE) {
        // We do not want this source plugin to have a cacheable count.
        // @see \Drupal\migrate_cache_counts_test\Plugin\migrate\source\CacheableEmbeddedDataSource
        return count($this->dataRows);
    }

}