struct SendableRecordBatchStream {
  // currently executing stream
  inner: SendableRecordBatchStream,
  // any batches that have been buffered so far
  batches: Vec<RecordBatch>,
  // current batch being shown
  current_batch: usize,
}

impl SendableRecordBatchStream {
  /// return the next batch in the stream
  async fn next(&self) -> &RecordBatch {
    self.current_batch += 1;
    self.current()
  }

  /// go to current_index
 async fn current(&self) -> &RecordBatch{
    while self.batches.len()+1 < current_batch {
      // fetch next batch from inner and put into self.batches
    }
    self.batches[self.current_batch]
  }
}