code: def _find_extra_chunks_for_offset_window(
      cls, op, inp, cur_chunk_index
  ):
      from ...indexing.loc import DataFrameLocGetItem
  
      # when window is offset, center=True is not supported
      assert not op.center
  
      axis = op.axis
      window = pd.Timedelta(op.window)
      ndim = inp.ndim
  
      # find prev chunks
      i = cur_chunk_index[axis]
      prev_chunks = []
      cur_index_min = inp.cix[cur_chunk_index].index_value.min_val
      start = cur_index_min - window
      assert cur_chunk_index is not None
      while i > 0:
          prev_chunk_index = list(cur_chunk_index)
          prev_chunk_index[axis] = i - 1
          prev_chunk_index = tuple(prev_chunk_index)
  
          prev_chunk = inp.cix[prev_chunk_index]
          prev_index_max = prev_chunk.index_value.max_val
          if prev_index_max >= start:
              slices = [slice(None)] * ndim
              slices[axis] = slice(start, None)
              prev_chunk_op = DataFrameLocGetItem(
                  indexes=slices,
                  output_types=prev_chunk.op.output_types,
              )
              slice_prev_chunk = prev_chunk_op.new_chunk([prev_chunk])
              prev_chunks.insert(0, slice_prev_chunk)
          else:
              # index max < start, break
              break
  
          i -= 1
  
      return prev_chunks, []
  
imports: import numpy
  import pandas
  from ....None import opcodes
  from ....core import recursive_tile
  from ....serialization.serializables import FieldTypes, AnyField, Int64Field, BoolField, StringField, Int32Field, KeyField, TupleField, DictField, ListField
  from ....utils import lazy_import, has_unknown_shape, pd_release_version, calc_nsplits
  from ...operands import DataFrameOperand, DataFrameOperandMixin
  from ...core import DATAFRAME_TYPE
  from ...utils import build_empty_df, build_empty_series, parse_index
label_desc: Use image node_id 19 for calling the DataFrameRollingAgg obj's underlying member method code with example usage: obj._find_extra_chunks_for_offset_window(cls, op, inp, cur_chunk_index) and returns: prev_chunks,  list