# Copyright 2018 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Abstract wrapper for deduplicating previously processed work."""

from __future__ import print_function
from __future__ import absolute_import
from __future__ import division


def CheckpointSequence(already_processed, save, sequence, limit=None):
  """Yields elements from |sequence| that haven't been processed, saving after.

  Args:
    already_processed: A callback which returns whether the item was already
        processed.
    save: A callback which checkpoints the given element.
    limit: The maximum number of elements to yield. Note this is not
        equivalent to itertools.islice(limit, _Checkpoint(...)) because the
        last element of that sequence would not be checkpointed.
    sequence: A sequence of elements to yield from
  """
  i = 0
  for item in sequence:
    if limit is not None and i >= limit:
      return
    if not already_processed(item):
      yield item
      save(item)
      i += 1