# Copyright 2019 The TensorFlow Authors. All Rights Reserved.
#
# 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,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Runs a ResNet model on the ImageNet dataset using custom training loops."""

import math
import os

from absl import app
from absl import flags
from absl import logging
import orbit
import tensorflow as tf

from official.modeling import performance
from official.utils.flags import core as flags_core
from official.utils.misc import distribution_utils
from official.utils.misc import keras_utils
from official.utils.misc import model_helpers
from official.vision.image_classification.resnet import common
from official.vision.image_classification.resnet import imagenet_preprocessing
from official.vision.image_classification.resnet import resnet_runnable

flags.DEFINE_boolean(name='use_tf_function', default=True,
                     help='Wrap the train and test step inside a '
                     'tf.function.')
flags.DEFINE_boolean(name='single_l2_loss_op', default=False,
                     help='Calculate L2_loss on concatenated weights, '
                     'instead of using Keras per-layer L2 loss.')


def build_stats(runnable, time_callback):
  """Normalizes and returns dictionary of stats.

  Args:
    runnable: The module containing all the training and evaluation metrics.
    time_callback: Time tracking callback instance.

  Returns:
    Dictionary of normalized results.
  """
  stats = {}

  if not runnable.flags_obj.skip_eval:
    stats['eval_loss'] = runnable.test_loss.result().numpy()
    stats['eval_acc'] = runnable.test_accuracy.result().numpy()

    stats['train_loss'] = runnable.train_loss.result().numpy()
    stats['train_acc'] = runnable.train_accuracy.result().numpy()

  if time_callback:
    timestamp_log = time_callback.timestamp_log
    stats['step_timestamp_log'] = timestamp_log
    stats['train_finish_time'] = time_callback.train_finish_time
    if time_callback.epoch_runtime_log:
      stats['avg_exp_per_second'] = time_callback.average_examples_per_second

  return stats


def get_num_train_iterations(flags_obj):
  """Returns the number of training steps, train and test epochs."""
  train_steps = (
      imagenet_preprocessing.NUM_IMAGES['train'] // flags_obj.batch_size)
  train_epochs = flags_obj.train_epochs

  if flags_obj.train_steps:
    train_steps = min(flags_obj.train_steps, train_steps)
    train_epochs = 1

  eval_steps = math.ceil(1.0 * imagenet_preprocessing.NUM_IMAGES['validation'] /
                         flags_obj.batch_size)

  return train_steps, train_epochs, eval_steps


def run(flags_obj):
  """Run ResNet ImageNet training and eval loop using custom training loops.

  Args:
    flags_obj: An object containing parsed flag values.

  Raises:
    ValueError: If fp16 is passed as it is not currently supported.

  Returns:
    Dictionary of training and eval stats.
  """
  keras_utils.set_session_config(
      enable_xla=flags_obj.enable_xla)
  performance.set_mixed_precision_policy(flags_core.get_tf_dtype(flags_obj))

  if tf.config.list_physical_devices('GPU'):
    if flags_obj.tf_gpu_thread_mode:
      keras_utils.set_gpu_thread_mode_and_count(
          per_gpu_thread_count=flags_obj.per_gpu_thread_count,
          gpu_thread_mode=flags_obj.tf_gpu_thread_mode,
          num_gpus=flags_obj.num_gpus,
          datasets_num_private_threads=flags_obj.datasets_num_private_threads)
    common.set_cudnn_batchnorm_mode()

  data_format = flags_obj.data_format
  if data_format is None:
    data_format = ('channels_first' if tf.config.list_physical_devices('GPU')
                   else 'channels_last')
  tf.keras.backend.set_image_data_format(data_format)

  strategy = distribution_utils.get_distribution_strategy(
      distribution_strategy=flags_obj.distribution_strategy,
      num_gpus=flags_obj.num_gpus,
      all_reduce_alg=flags_obj.all_reduce_alg,
      num_packs=flags_obj.num_packs,
      tpu_address=flags_obj.tpu)

  per_epoch_steps, train_epochs, eval_steps = get_num_train_iterations(
      flags_obj)
  if not flags_obj.steps_per_loop:
    steps_per_loop = per_epoch_steps
  elif flags_obj.steps_per_loop > per_epoch_steps:
    steps_per_loop = per_epoch_steps
    logging.warn('Setting steps_per_loop to %d to respect epoch boundary.',
                 steps_per_loop)
  else:
    steps_per_loop = flags_obj.steps_per_loop

  logging.info(
      'Training %d epochs, each epoch has %d steps, '
      'total steps: %d; Eval %d steps', train_epochs, per_epoch_steps,
      train_epochs * per_epoch_steps, eval_steps)

  time_callback = keras_utils.TimeHistory(
      flags_obj.batch_size,
      flags_obj.log_steps,
      logdir=flags_obj.model_dir if flags_obj.enable_tensorboard else None)
  with distribution_utils.get_strategy_scope(strategy):
    runnable = resnet_runnable.ResnetRunnable(flags_obj, time_callback,
                                              per_epoch_steps)

  eval_interval = flags_obj.epochs_between_evals * per_epoch_steps
  checkpoint_interval = (
      steps_per_loop * 5 if flags_obj.enable_checkpoint_and_export else None)
  summary_interval = steps_per_loop if flags_obj.enable_tensorboard else None

  checkpoint_manager = tf.train.CheckpointManager(
      runnable.checkpoint,
      directory=flags_obj.model_dir,
      max_to_keep=10,
      step_counter=runnable.global_step,
      checkpoint_interval=checkpoint_interval)

  resnet_controller = orbit.Controller(
      strategy,
      runnable,
      runnable if not flags_obj.skip_eval else None,
      global_step=runnable.global_step,
      steps_per_loop=steps_per_loop,
      checkpoint_manager=checkpoint_manager,
      summary_interval=summary_interval,
      eval_summary_dir=os.path.join(flags_obj.model_dir, 'eval'))

  time_callback.on_train_begin()
  if not flags_obj.skip_eval:
    resnet_controller.train_and_evaluate(
        train_steps=per_epoch_steps * train_epochs,
        eval_steps=eval_steps,
        eval_interval=eval_interval)
  else:
    resnet_controller.train(steps=per_epoch_steps * train_epochs)
  time_callback.on_train_end()

  stats = build_stats(runnable, time_callback)
  return stats


def main(_):
  model_helpers.apply_clean(flags.FLAGS)
  stats = run(flags.FLAGS)
  logging.info('Run stats:\n%s', stats)


if __name__ == '__main__':
  logging.set_verbosity(logging.INFO)
  common.define_keras_flags()
  app.run(main)
