# Copyright 2022 DeepMind Technologies Limited
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
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"""Defines the interface for a checkpointer."""

from typing import Optional, TypeVar, Protocol


CheckpointableState = TypeVar("CheckpointableState")


class Checkpointer(Protocol[CheckpointableState]):
  """The interface that checkpoints must satisfy to work with the benchmarker.

  The checkpointer must support reading and writing checkpointable state.
  """

  def write(self, state: CheckpointableState) -> None:
    """Writes a checkpoint.

    Args:
      state: Arbitrary checkpointable state
    """

  def restore(self) -> Optional[CheckpointableState]:
    """Restores the most recent checkpointed state.

    Returns:
      The most recent checkpoint that was successfully written using write,
      or None if no checkpoint state is available.
    """
