# Copyright 2020 The HuggingFace Team. 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.
"""Tensorflow trainer class."""

import datetime
import math
import os
from typing import Callable, Dict, Optional, Tuple


# Integrations must be imported before ML frameworks:
from .integrations import (  # isort: split
    is_comet_available,
    is_wandb_available,
)

import numpy as np
import tensorflow as tf
from packaging.version import parse
from tensorflow.python.distribute.values import PerReplica

from .modeling_tf_utils import TFPreTrainedModel
from .optimization_tf import GradientAccumulator, create_optimizer
from .trainer_utils import PREFIX_CHECKPOINT_DIR, EvalPrediction, EvaluationStrategy, PredictionOutput, set_seed
from .training_args_tf import TFTrainingArguments
from .utils import logging


if is_wandb_available():
    import wandb

if is_comet_available():
    import comet_ml

logger = logging.get_logger(__name__)


class TFTrainer:
    """
    TFTrainer is a simple but feature-complete training and eval loop for TensorFlow, optimized for 🤗 Transformers.

    Args:
        model (:class:`~transformers.TFPreTrainedModel`):
            The model to train, evaluate or use for predictions.
        args (:class:`~transformers.TFTrainingArguments`):
            The arguments to tweak training.
        train_dataset (:class:`~tf.data.Dataset`, `optional`):
            The dataset to use for training. The dataset should yield tuples of ``(features, labels)`` where
            ``features`` is a dict of input features and ``labels`` is the labels. If ``labels`` is a tensor, the loss
            is calculated by the model by calling ``model(features, labels=labels)``. If ``labels`` is a dict, such as
            when using a QuestionAnswering head model with multiple targets, the loss is instead calculated by calling
            ``model(features, **labels)``.
        eval_dataset (:class:`~tf.data.Dataset`, `optional`):
            The dataset to use for evaluation. The dataset should yield tuples of ``(features, labels)`` where
            ``features`` is a dict of input features and ``labels`` is the labels. If ``labels`` is a tensor, the loss
            is calculated by the model by calling ``model(features, labels=labels)``. If ``labels`` is a dict, such as
            when using a QuestionAnswering head model with multiple targets, the loss is instead calculated by calling
            ``model(features, **labels)``.
        compute_metrics (:obj:`Callable[[EvalPrediction], Dict]`, `optional`):
            The function that will be used to compute metrics at evaluation. Must take a
            :class:`~transformers.EvalPrediction` and return a dictionary string to metric values.
        tb_writer (:obj:`tf.summary.SummaryWriter`, `optional`):
            Object to write to TensorBoard.
        optimizers (:obj:`Tuple[tf.keras.optimizers.Optimizer, tf.keras.optimizers.schedules.LearningRateSchedule]`, `optional`):
            A tuple containing the optimizer and the scheduler to use. The optimizer default to an instance of
            :class:`tf.keras.optimizers.Adam` if :obj:`args.weight_decay_rate` is 0 else an instance of
            :class:`~transformers.AdamWeightDecay`. The scheduler will default to an instance of
            :class:`tf.keras.optimizers.schedules.PolynomialDecay` if :obj:`args.num_warmup_steps` is 0 else an
            instance of :class:`~transformers.WarmUp`.
    """

    def __init__(
        self,
        model: TFPreTrainedModel,
        args: TFTrainingArguments,
        train_dataset: Optional[tf.data.Dataset] = None,
        eval_dataset: Optional[tf.data.Dataset] = None,
        compute_metrics: Optional[Callable[[EvalPrediction], Dict]] = None,
        tb_writer: Optional[tf.summary.SummaryWriter] = None,
        optimizers: Tuple[tf.keras.optimizers.Optimizer, tf.keras.optimizers.schedules.LearningRateSchedule] = (
            None,
            None,
        ),
    ):
        assert parse(tf.__version__).release >= (2, 2, 0), (
            "You need to run the TensorFlow trainer with at least the version 2.2.0, your version is %r "
            % tf.__version__
        )

        self.model = model
        self.args = args
        self.train_dataset = train_dataset
        self.eval_dataset = eval_dataset
        self.compute_metrics = compute_metrics
        self.optimizer, self.lr_scheduler = optimizers
        self.gradient_accumulator = GradientAccumulator()
        self.global_step = 0
        self.epoch_logging = 0

        if tb_writer is not None:
            self.tb_writer = tb_writer
        else:
            self.tb_writer = tf.summary.create_file_writer(self.args.logging_dir)

        if is_wandb_available():
            self.setup_wandb()
        elif os.environ.get("WANDB_DISABLED") != "true":
            logger.info(
                "You are instantiating a Trainer but W&B is not installed. To use wandb logging, "
                "run `pip install wandb; wandb login` see https://docs.wandb.com/huggingface."
            )

        if is_comet_available():
            self.setup_comet()
        elif os.environ.get("COMET_MODE") != "DISABLED":
            logger.info(
                "To use comet_ml logging, run `pip/conda install comet_ml` "
                "see https://www.comet.ml/docs/python-sdk/huggingface/"
            )

        set_seed(self.args.seed)

    def get_train_tfdataset(self) -> tf.data.Dataset:
        """
        Returns the training :class:`~tf.data.Dataset`.

        Subclass and override this method if you want to inject some custom behavior.
        """
        if self.train_dataset is None:
            raise ValueError("Trainer: training requires a train_dataset.")

        self.total_train_batch_size = self.args.train_batch_size * self.args.gradient_accumulation_steps
        self.num_train_examples = tf.data.experimental.cardinality(self.train_dataset).numpy()

        if self.num_train_examples < 0:
            raise ValueError("The training dataset must have an asserted cardinality")

        ds = (
            self.train_dataset.repeat()
            .shuffle(self.num_train_examples, seed=self.args.seed)
            .batch(self.total_train_batch_size, drop_remainder=self.args.dataloader_drop_last)
            .prefetch(tf.data.experimental.AUTOTUNE)
        )

        return self.args.strategy.experimental_distribute_dataset(ds)

    def get_eval_tfdataset(self, eval_dataset: Optional[tf.data.Dataset] = None) -> tf.data.Dataset:
        """
        Returns the evaluation :class:`~tf.data.Dataset`.

        Args:
            eval_dataset (:class:`~tf.data.Dataset`, `optional`):
                If provided, will override `self.eval_dataset`. The dataset should yield tuples of ``(features,
                labels)`` where ``features`` is a dict of input features and ``labels`` is the labels. If ``labels`` is
                a tensor, the loss is calculated by the model by calling ``model(features, labels=labels)``. If
                ``labels`` is a dict, such as when using a QuestionAnswering head model with multiple targets, the loss
                is instead calculated by calling ``model(features, **labels)``.

        Subclass and override this method if you want to inject some custom behavior.
        """
        if eval_dataset is None and self.eval_dataset is None:
            raise ValueError("Trainer: evaluation requires an eval_dataset.")

        eval_dataset = eval_dataset if eval_dataset is not None else self.eval_dataset
        num_examples = tf.data.experimental.cardinality(eval_dataset).numpy()

        if num_examples < 0:
            raise ValueError("The training dataset must have an asserted cardinality")

        approx = math.floor if self.args.dataloader_drop_last else math.ceil
        steps = approx(num_examples / self.args.eval_batch_size)
        ds = (
            eval_dataset.repeat()
            .batch(self.args.eval_batch_size, drop_remainder=self.args.dataloader_drop_last)
            .prefetch(tf.data.experimental.AUTOTUNE)
        )

        return self.args.strategy.experimental_distribute_dataset(ds), steps, num_examples

    def get_test_tfdataset(self, test_dataset: tf.data.Dataset) -> tf.data.Dataset:
        """
        Returns a test :class:`~tf.data.Dataset`.

        Args:
            test_dataset (:class:`~tf.data.Dataset`):
                The dataset to use. The dataset should yield tuples of ``(features, labels)`` where ``features`` is a
                dict of input features and ``labels`` is the labels. If ``labels`` is a tensor, the loss is calculated
                by the model by calling ``model(features, labels=labels)``. If ``labels`` is a dict, such as when using
                a QuestionAnswering head model with multiple targets, the loss is instead calculated by calling
                ``model(features, **labels)``.

        Subclass and override this method if you want to inject some custom behavior.
        """

        num_examples = tf.data.experimental.cardinality(test_dataset).numpy()

        if num_examples < 0:
            raise ValueError("The training dataset must have an asserted cardinality")

        approx = math.floor if self.args.dataloader_drop_last else math.ceil
        steps = approx(num_examples / self.args.eval_batch_size)
        ds = (
            test_dataset.repeat()
            .batch(self.args.eval_batch_size, drop_remainder=self.args.dataloader_drop_last)
            .prefetch(tf.data.experimental.AUTOTUNE)
        )

        return self.args.strategy.experimental_distribute_dataset(ds), steps, num_examples

    def create_optimizer_and_scheduler(self, num_training_steps: int):
        """
        Setup the optimizer and the learning rate scheduler.

        We provide a reasonable default that works well. If you want to use something else, you can pass a tuple in the
        TFTrainer's init through :obj:`optimizers`, or subclass and override this method.
        """
        if not self.optimizer and not self.lr_scheduler:
            self.optimizer, self.lr_scheduler = create_optimizer(
                self.args.learning_rate,
                num_training_steps,
                self.args.warmup_steps,
                adam_beta1=self.args.adam_beta1,
                adam_beta2=self.args.adam_beta2,
                adam_epsilon=self.args.adam_epsilon,
                weight_decay_rate=self.args.weight_decay,
                power=self.args.poly_power,
            )

    def setup_wandb(self):
        """
        Setup the optional Weights & Biases (`wandb`) integration.

        One can subclass and override this method to customize the setup if needed. Find more information `here
        <https://docs.wandb.com/huggingface>`__. You can also override the following environment variables:

        Environment:
            WANDB_PROJECT:
                (Optional): str - "huggingface" by default, set this to a custom string to store results in a different
                project.
            WANDB_DISABLED:
                (Optional): boolean - defaults to false, set to "true" to disable wandb entirely.
        """

        logger.info('Automatic Weights & Biases logging enabled, to disable set os.environ["WANDB_DISABLED"] = "true"')
        combined_dict = {**self.model.config.to_dict(), **self.args.to_sanitized_dict()}
        wandb.init(project=os.getenv("WANDB_PROJECT", "huggingface"), config=combined_dict, name=self.args.run_name)

    def setup_comet(self):
        """
        Setup the optional Comet.ml integration.

        Environment:
            COMET_MODE:
                (Optional): str - "OFFLINE", "ONLINE", or "DISABLED"
            COMET_PROJECT_NAME:
                (Optional): str - Comet.ml project name for experiments
            COMET_OFFLINE_DIRECTORY:
                (Optional): str - folder to use for saving offline experiments when `COMET_MODE` is "OFFLINE"

        For a number of configurable items in the environment, see `here
        <https://www.comet.ml/docs/python-sdk/advanced/#comet-configuration-variables>`__
        """
        comet_mode = os.getenv("COMET_MODE", "ONLINE").upper()
        args = {"project_name": os.getenv("COMET_PROJECT_NAME", "huggingface")}
        experiment = None
        if comet_mode == "ONLINE":
            experiment = comet_ml.Experiment(**args)
            logger.info("Automatic Comet.ml online logging enabled")
        elif comet_mode == "OFFLINE":
            args["offline_directory"] = os.getenv("COMET_OFFLINE_DIRECTORY", "./")
            experiment = comet_ml.OfflineExperiment(**args)
            logger.info("Automatic Comet.ml offline logging enabled; use `comet upload` when finished")
        if experiment is not None:
            experiment._set_model_graph(self.model, framework="transformers")
            experiment._log_parameters(self.args, prefix="args/", framework="transformers")
            experiment._log_parameters(self.model.config, prefix="config/", framework="transformers")

    def prediction_loop(
        self,
        dataset: tf.data.Dataset,
        steps: int,
        num_examples: int,
        description: str,
        prediction_loss_only: Optional[bool] = None,
    ) -> PredictionOutput:
        """
        Prediction/evaluation loop, shared by :func:`~transformers.TFTrainer.evaluate` and
        :func:`~transformers.TFTrainer.predict`.

        Works both with or without labels.
        """

        prediction_loss_only = (
            prediction_loss_only if prediction_loss_only is not None else self.args.prediction_loss_only
        )

        logger.info("***** Running %s *****", description)
        logger.info("  Num examples = %d", num_examples)
        logger.info("  Batch size = %d", self.args.eval_batch_size)

        label_ids: np.ndarray = None
        preds: np.ndarray = None
        self.eval_loss = tf.keras.metrics.Sum()

        # Reset the past mems state at the beginning of the evaluation if necessary.
        if self.args.past_index >= 0:
            self._past = None

        for step, batch in enumerate(dataset):
            logits = self.distributed_prediction_steps(batch)
            _, labels = batch

            if not prediction_loss_only:
                if isinstance(logits, tuple):
                    logits = logits[0]

                if isinstance(labels, tuple):
                    labels = labels[0]

                if self.args.n_replicas > 1:
                    for val in logits.values:
                        if preds is None:
                            preds = val.numpy()
                        else:
                            preds = np.append(preds, val.numpy(), axis=0)

                    for val in labels.values:
                        if label_ids is None:
                            label_ids = val.numpy()
                        else:
                            label_ids = np.append(label_ids, val.numpy(), axis=0)
                else:
                    if preds is None:
                        preds = logits.numpy()
                    else:
                        preds = np.append(preds, logits.numpy(), axis=0)

                    if label_ids is None:
                        label_ids = labels.numpy()
                    else:
                        label_ids = np.append(label_ids, labels.numpy(), axis=0)

                if step == steps:
                    break

        if self.compute_metrics is not None and preds is not None and label_ids is not None:
            metrics = self.compute_metrics(EvalPrediction(predictions=preds, label_ids=label_ids))
        else:
            metrics = {}

        metrics["eval_loss"] = self.eval_loss.result().numpy() / steps

        for key in list(metrics.keys()):
            if not key.startswith("eval_"):
                metrics[f"eval_{key}"] = metrics.pop(key)

        if self.args.past_index and hasattr(self, "_past"):
            # Clean the state at the end of training
            delattr(self, "_past")

        return PredictionOutput(predictions=preds, label_ids=label_ids, metrics=metrics)

    def log(self, logs: Dict[str, float]) -> None:
        """
        Log :obj:`logs` on the various objects watching training.

        Subclass and override this method to inject custom behavior.

        Args:
            logs (:obj:`Dict[str, float]`):
                The values to log.
        """
        logs["epoch"] = self.epoch_logging

        if self.tb_writer:
            with self.tb_writer.as_default():
                for k, v in logs.items():
                    tf.summary.scalar(k, v, step=self.global_step)
            self.tb_writer.flush()

        if is_wandb_available():
            wandb.log(logs, step=self.global_step)

        if is_comet_available():
            experiment = comet_ml.config.get_global_experiment()
            if experiment is not None:
                experiment._log_metrics(
                    logs, step=self.global_step, epoch=self.epoch_logging, framework="transformers"
                )

        output = {**logs, **{"step": self.global_step}}

        logger.info(output)

    def evaluate(self, eval_dataset: Optional[tf.data.Dataset] = None) -> Dict[str, float]:
        """
        Run evaluation and returns metrics.

        The calling script will be responsible for providing a method to compute metrics, as they are task-dependent
        (pass it to the init :obj:`compute_metrics` argument).

        Args:
            eval_dataset (:class:`~tf.data.Dataset`, `optional`):
                Pass a dataset if you wish to override :obj:`self.eval_dataset`. The dataset should yield tuples of
                ``(features, labels)`` where ``features`` is a dict of input features and ``labels`` is the labels. If
                ``labels`` is a tensor, the loss is calculated by the model by calling ``model(features,
                labels=labels)``. If ``labels`` is a dict, such as when using a QuestionAnswering head model with
                multiple targets, the loss is instead calculated by calling ``model(features, **labels)``.

        Returns:
            A dictionary containing the evaluation loss and the potential metrics computed from the predictions.
        """
        eval_ds, steps, num_examples = self.get_eval_tfdataset(eval_dataset)

        output = self.prediction_loop(eval_ds, steps, num_examples, description="Evaluation")
        logs = {**output.metrics}
        logs["epoch"] = self.epoch_logging

        self.log(logs)

        return output.metrics

    def prediction_step(
        self, features: tf.Tensor, labels: tf.Tensor, nb_instances_in_global_batch: tf.Tensor
    ) -> tf.Tensor:
        """
        Compute the prediction on features and update the loss with labels.

        Subclass and override to inject some custom behavior.
        """
        per_example_loss, logits = self.run_model(features, labels, False)
        scaled_loss = per_example_loss / tf.cast(nb_instances_in_global_batch, dtype=per_example_loss.dtype)

        self.eval_loss.update_state(scaled_loss)

        return logits

    @tf.function
    def distributed_prediction_steps(self, batch):

        nb_instances_in_batch = self._compute_nb_instances(batch)
        inputs = self._get_step_inputs(batch, nb_instances_in_batch)

        logits = self.args.strategy.run(self.prediction_step, inputs)

        return logits

    def train(self) -> None:
        """
        Train method to train the model.
        """
        train_ds = self.get_train_tfdataset()

        if self.args.debug:
            tf.summary.trace_on(graph=True, profiler=True)

        self.gradient_accumulator.reset()

        num_update_steps_per_epoch = self.num_train_examples / self.total_train_batch_size

        # In fact, ``self.args.dataloader_drop_last`` has no effect in `trainer_tf.py`, because
        # the dataset is repeated before being batched.
        # It has the effect only when TPU is used which requires explicit tensor shape in order to make
        # the gradient accumulation implementation work.
        approx = math.floor if self.args.dataloader_drop_last else math.ceil
        num_update_steps_per_epoch = approx(num_update_steps_per_epoch)

        # At least one update for each epoch.
        num_update_steps_per_epoch = max(num_update_steps_per_epoch, 1)
        self.steps_per_epoch = num_update_steps_per_epoch

        if self.args.max_steps > 0:
            t_total = self.args.max_steps
            epochs = (self.args.max_steps // self.steps_per_epoch) + int(
                self.args.max_steps % self.steps_per_epoch > 0
            )
        else:
            t_total = self.steps_per_epoch * self.args.num_train_epochs
            epochs = self.args.num_train_epochs

        # Since ``self.args.num_train_epochs`` can be `float`, we make ``epochs`` be a `float` always.
        epochs = float(epochs)

        with self.args.strategy.scope():
            self.create_optimizer_and_scheduler(num_training_steps=t_total)
            folder = os.path.join(self.args.output_dir, PREFIX_CHECKPOINT_DIR)
            ckpt = tf.train.Checkpoint(optimizer=self.optimizer, model=self.model)
            self.model.ckpt_manager = tf.train.CheckpointManager(ckpt, folder, max_to_keep=self.args.save_total_limit)

            iterations = self.optimizer.iterations
            epochs_trained = 0
            steps_trained_in_current_epoch = 0
            if self.model.ckpt_manager.latest_checkpoint:

                logger.info(
                    "Checkpoint file %s found and restoring from checkpoint", self.model.ckpt_manager.latest_checkpoint
                )
                ckpt.restore(self.model.ckpt_manager.latest_checkpoint).expect_partial()

                self.global_step = iterations.numpy()

                epochs_trained = self.global_step // self.steps_per_epoch
                steps_trained_in_current_epoch = self.global_step % self.steps_per_epoch

                logger.info("  Continuing training from checkpoint, will skip to saved global_step")
                logger.info("  Continuing training from epoch %d", epochs_trained)
                logger.info("  Continuing training from global step %d", self.global_step)
                logger.info("  Will skip the first %d steps in the first epoch", steps_trained_in_current_epoch)

            tf.summary.experimental.set_step(self.global_step)

            with self.tb_writer.as_default():
                tf.summary.text("args", self.args.to_json_string())

            self.tb_writer.flush()

            logger.info("***** Running training *****")
            logger.info("  Num examples = %d", self.num_train_examples)
            # TODO: We might want to print a more precise ``epochs`` if self.args.max_steps > 0 ?
            logger.info("  Num Epochs = %d", epochs)
            logger.info("  Instantaneous batch size per device = %d", self.args.per_device_train_batch_size)
            logger.info(
                "  Total train batch size (w. parallel, distributed & accumulation) = %d", self.total_train_batch_size
            )
            logger.info("  Gradient Accumulation steps = %d", self.args.gradient_accumulation_steps)
            logger.info("  Steps per epoch = %d", self.steps_per_epoch)
            logger.info("  Total optimization steps = %d", t_total)

            self.train_loss = tf.keras.metrics.Sum()
            start_time = datetime.datetime.now()

            for epoch_iter in range(epochs_trained, int(epochs)):
                # Reset the past mems state at the beginning of each epoch if necessary.
                if self.args.past_index >= 0:
                    self._past = None

                for step, batch in enumerate(train_ds):

                    # Skip past any already trained steps if resuming training
                    if steps_trained_in_current_epoch > 0:
                        steps_trained_in_current_epoch -= 1
                        continue

                    self.distributed_training_steps(batch)

                    self.global_step = iterations.numpy()
                    self.epoch_logging = epoch_iter + (step + 1) / self.steps_per_epoch

                    training_loss = self.train_loss.result() / (step + 1)

                    if self.args.debug:
                        logs = {}
                        logs["loss"] = training_loss.numpy()
                        logs["epoch"] = self.epoch_logging

                        self.log(logs)

                    if self.global_step == 1 and self.args.debug:
                        with self.tb_writer.as_default():
                            tf.summary.trace_export(
                                name="training", step=self.global_step, profiler_outdir=self.args.logging_dir
                            )

                    if (
                        self.args.eval_steps > 0
                        and self.args.evaluation_strategy == EvaluationStrategy.STEPS
                        and self.global_step % self.args.eval_steps == 0
                    ):
                        self.evaluate()

                    if (self.args.logging_steps > 0 and self.global_step % self.args.logging_steps == 0) or (
                        self.global_step == 1 and self.args.logging_first_step
                    ):
                        logs = {}
                        logs["loss"] = training_loss.numpy()
                        logs["learning_rate"] = self.lr_scheduler(self.global_step).numpy()
                        logs["epoch"] = self.epoch_logging

                        self.log(logs)

                    if self.args.save_steps > 0 and self.global_step % self.args.save_steps == 0:
                        ckpt_save_path = self.model.ckpt_manager.save()

                        logger.info("Saving checkpoint for step {} at {}".format(self.global_step, ckpt_save_path))

                    if self.args.max_steps > 0 and self.global_step >= t_total:
                        break

                    if self.global_step % self.steps_per_epoch == 0:
                        break

                self.train_loss.reset_states()

                if self.args.max_steps > 0 and self.global_step >= self.args.max_steps:
                    break

            end_time = datetime.datetime.now()

            logger.info("Training took: {}".format(str(end_time - start_time)))

        if self.args.past_index and hasattr(self, "_past"):
            # Clean the state at the end of training
            delattr(self, "_past")

    def training_step(self, features, labels, nb_instances_in_global_batch):
        """
        Perform a training step on features and labels.

        Subclass and override to inject some custom behavior.
        """
        per_example_loss, _ = self.run_model(features, labels, True)
        scaled_loss = per_example_loss / tf.cast(nb_instances_in_global_batch, dtype=per_example_loss.dtype)
        gradients = tf.gradients(scaled_loss, self.model.trainable_variables)
        gradients = [
            g if g is not None else tf.zeros_like(v) for g, v in zip(gradients, self.model.trainable_variables)
        ]

        if self.args.gradient_accumulation_steps > 1:
            self.gradient_accumulator(gradients)

        self.train_loss.update_state(scaled_loss)

        if self.args.gradient_accumulation_steps == 1:
            return gradients

    def apply_gradients(self, features, labels, nb_instances_in_global_batch):
        if self.args.gradient_accumulation_steps == 1:
            gradients = self.training_step(features, labels, nb_instances_in_global_batch)

            self.optimizer.apply_gradients(list(zip(gradients, self.model.trainable_variables)))
        else:
            for _ in tf.range(self.args.gradient_accumulation_steps):
                reduced_features = {
                    k: ft[: self.args.train_batch_size // self.args.n_replicas] for k, ft in features.items()
                }
                reduced_labels = labels[: self.args.train_batch_size // self.args.n_replicas]

                self.training_step(reduced_features, reduced_labels, nb_instances_in_global_batch)

                features = {
                    k: tf.concat(
                        [ft[self.args.train_batch_size // self.args.n_replicas :], reduced_features[k]],
                        axis=0,
                    )
                    for k, ft in features.items()
                }

                labels = tf.concat(
                    [labels[self.args.train_batch_size // self.args.n_replicas :], reduced_labels], axis=0
                )

            gradients = self.gradient_accumulator.gradients
            gradients = [
                (tf.clip_by_value(grad, -self.args.max_grad_norm, self.args.max_grad_norm)) for grad in gradients
            ]

            self.optimizer.apply_gradients(list(zip(gradients, self.model.trainable_variables)))
            self.gradient_accumulator.reset()

    @tf.function
    def distributed_training_steps(self, batch):
        with self.args.strategy.scope():

            nb_instances_in_batch = self._compute_nb_instances(batch)
            inputs = self._get_step_inputs(batch, nb_instances_in_batch)

            self.args.strategy.run(self.apply_gradients, inputs)

    @staticmethod
    def _compute_nb_instances(batch):

        labels = batch[-1]
        if isinstance(labels, PerReplica):
            labels = tf.concat(labels.values, axis=0)

        nb_instances = tf.reduce_sum(tf.cast(labels != -100, dtype=tf.int32))

        return nb_instances

    @staticmethod
    def _get_step_inputs(batch, nb_instances):

        features, labels = batch

        if isinstance(labels, PerReplica):
            # need to make a `PerReplica` objects for ``nb_instances``
            nb_instances = PerReplica([nb_instances] * len(labels.values))

        step_inputs = (features, labels, nb_instances)

        return step_inputs

    def run_model(self, features, labels, training):
        """
        Computes the loss of the given features and labels pair.

        Subclass and override this method if you want to inject some custom behavior.

        Args:
            features (:obj:`tf.Tensor`): A batch of input features.
            labels (:obj:`tf.Tensor`): A batch of labels.
            training (:obj:`bool`): Whether or not to run the model in training mode.

        Returns:
            A tuple of two :obj:`tf.Tensor`: The loss and logits.
        """

        if self.args.past_index >= 0 and getattr(self, "_past", None) is not None:
            features["mems"] = self._past

        if isinstance(labels, (dict)):
            outputs = self.model(features, training=training, **labels)[:2]
        else:
            outputs = self.model(features, labels=labels, training=training)[:2]

        loss, logits = outputs[:2]

        if self.args.past_index >= 0:
            self._past = outputs[self.args.past_index]

        return loss, logits

    def predict(self, test_dataset: tf.data.Dataset) -> PredictionOutput:
        """
        Run prediction and returns predictions and potential metrics.

        Depending on the dataset and your use case, your test dataset may contain labels. In that case, this method
        will also return metrics, like in :obj:`evaluate()`.

        Args:
            test_dataset (:class:`~tf.data.Dataset`):
                Dataset to run the predictions on. The dataset should yield tuples of ``(features, labels)`` where
                ``features`` is a dict of input features and ``labels`` is the labels. If ``labels`` is a tensor, the
                loss is calculated by the model by calling ``model(features, labels=labels)``. If ``labels`` is a dict,
                such as when using a QuestionAnswering head model with multiple targets, the loss is instead calculated
                by calling ``model(features, **labels)``

        Returns: `NamedTuple` A namedtuple with the following keys:

            - predictions (:obj:`np.ndarray`): The predictions on :obj:`test_dataset`.
            - label_ids (:obj:`np.ndarray`, `optional`): The labels (if the dataset contained some).
            - metrics (:obj:`Dict[str, float]`, `optional`): The potential dictionary of metrics (if the dataset
              contained labels).
        """
        test_ds, steps, num_examples = self.get_test_tfdataset(test_dataset)

        return self.prediction_loop(test_ds, steps, num_examples, description="Prediction")

    def save_model(self, output_dir: Optional[str] = None):
        """
        Will save the model, so you can reload it using :obj:`from_pretrained()`.
        """
        output_dir = output_dir if output_dir is not None else self.args.output_dir

        logger.info("Saving model in {}".format(output_dir))

        if not isinstance(self.model, TFPreTrainedModel):
            raise ValueError("Trainer.model appears to not be a PreTrainedModel")

        self.model.save_pretrained(output_dir)
