# Copyright 2021 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.

from typing import Any, Dict, List, Optional, Tuple, Union

import torch
from torch import nn
from torch.utils.data.dataset import Dataset
from torch.utils.data.distributed import DistributedSampler

from ..trainer import Trainer
from ..trainer_pt_utils import (
    DistributedLengthGroupedSampler,
    SequentialDistributedSampler,
    nested_detach,
    nested_numpify,
)
from ..utils import logging
from .training_args_sm import is_smdistributed_available


logger = logging.get_logger(__name__)


if is_smdistributed_available():
    import smdistributed.modelparallel.torch as smp

    @smp.step()
    def forward_backward(model, inputs):
        outputs = model(**inputs)
        loss = outputs["loss"] if isinstance(outputs, dict) else outputs[0]
        model.backward(loss)
        return loss

    @smp.step()
    def forward_only(model, inputs):
        return model(**inputs)

    def smp_gather(tensor):
        if isinstance(tensor, (list, tuple)):
            return type(tensor)(smp_gather(t) for t in tensor)
        elif isinstance(tensor, dict):
            return type(tensor)({k: smp_gather(v) for k, v in tensor.items()})
        elif not isinstance(tensor, torch.Tensor):
            raise TypeError(
                f"Can't gather the values of type {type(tensor)}, only of nested list/tuple/dicts of tensors."
            )
        all_tensors = smp.allgather(tensor, smp.CommGroup.DP_GROUP)
        return torch.cat([t.cpu() for t in all_tensors], dim=0)

    def nested_smp_concat(tensor):
        if isinstance(tensor, (list, tuple)):
            return type(tensor)(nested_smp_concat(t) for t in tensor)
        elif isinstance(tensor, dict):
            return type(tensor)({k: nested_smp_concat(v) for k, v in tensor.items()})
        # It doesn't seem possible to check here if `tensor` is a StepOutput because StepOutput lives in `smp.step`
        # which is also the name of the decorator so Python is confused.
        return tensor.concat().detach().cpu()


class SageMakerTrainer(Trainer):
    def __init__(self, args=None, **kwargs):
        super().__init__(args=args, **kwargs)
        self.is_model_parallel_enabled = is_smdistributed_available() and self.args.mp_parameters != ""
        if self.is_model_parallel_enabled and self.args.gradient_accumulation_steps != 1:
            raise ValueError("Gradient accumulation is not supported when model parallel is enabled.")

    def _get_train_sampler(self):
        if self.is_model_parallel_enabled:
            if self.args.group_by_length:
                return DistributedLengthGroupedSampler(
                    self.train_dataset, self.args.train_batch_size, num_replicas=smp.dp_size(), rank=smp.dp_rank()
                )
            else:
                return DistributedSampler(self.train_dataset, num_replicas=smp.dp_size(), rank=smp.dp_rank())
        else:
            return super()._get_train_sampler()

    def _get_eval_sampler(self, eval_dataset: Dataset) -> Optional[torch.utils.data.sampler.Sampler]:
        if self.is_model_parallel_enabled:
            return SequentialDistributedSampler(eval_dataset, num_replicas=smp.dp_size(), rank=smp.dp_rank())
        else:
            return super()._get_eval_sampler(eval_dataset)

    def _wrap_model(self, model, training=True):
        if self.is_model_parallel_enabled:
            # Wrapping the base model twice in a DistributedModel will raise an error.
            if isinstance(self.model_wrapped, smp.model.DistributedModel):
                return self.model_wrapped
            return smp.DistributedModel(model)
        else:
            return super()._wrap_model(model)

    def create_optimizer_and_scheduler(self, num_training_steps: int):
        super().create_optimizer_and_scheduler(num_training_steps)
        if self.is_model_parallel_enabled:
            self.optimizer = smp.DistributedOptimizer(self.optimizer)

    def training_step(self, model: nn.Module, inputs: Dict[str, Union[torch.Tensor, Any]]) -> torch.Tensor:
        if self.is_model_parallel_enabled:
            model.train()
            inputs = self._prepare_inputs(inputs)
            loss_mb = forward_backward(model, inputs)
            return loss_mb.reduce_mean().detach().to(self.args.device)
        else:
            return super().training_step(model, inputs)

    def _gather_and_numpify(self, tensors, name):
        if self.is_model_parallel_enabled:
            tensors = smp_gather(tensors)
            return nested_numpify(tensors)
        else:
            return super()._gather_and_numpify(tensors, name)

    def prediction_step(
        self,
        model: nn.Module,
        inputs: Dict[str, Union[torch.Tensor, Any]],
        prediction_loss_only: bool,
        ignore_keys: Optional[List[str]] = None,
    ) -> Tuple[Optional[float], Optional[torch.Tensor], Optional[torch.Tensor]]:
        if self.is_model_parallel_enabled:
            has_labels = all(inputs.get(k) is not None for k in self.label_names)
            inputs = self._prepare_inputs(inputs)

            if ignore_keys is None:
                if hasattr(self.model, "config"):
                    ignore_keys = getattr(self.model.config, "keys_to_ignore_at_inference", [])
                else:
                    ignore_keys = []

            with torch.no_grad():
                raw_outputs = forward_only(model, inputs)
                if has_labels:
                    if isinstance(raw_outputs, dict):
                        loss_mb = raw_outputs["loss"]
                        logits_mb = tuple(v for k, v in raw_outputs.items() if k not in ignore_keys + ["loss"])
                    else:
                        loss_mb = raw_outputs[0]
                        logits_mb = raw_outputs[1:]

                    loss = loss_mb.reduce_mean().detach().cpu()
                    logits = nested_smp_concat(logits_mb)
                else:
                    loss = None
                    if isinstance(raw_outputs, dict):
                        logits_mb = tuple(v for k, v in raw_outputs.items() if k not in ignore_keys)
                    else:
                        logits_mb = raw_outputs
                    logits = nested_smp_concat(logits_mb)

            if prediction_loss_only:
                return (loss, None, None)

            if len(logits) == 1:
                logits = logits[0]

            if has_labels:
                labels = nested_detach(tuple(inputs.get(name) for name in self.label_names))
                if len(labels) == 1:
                    labels = labels[0]
            else:
                labels = None

            return (loss, logits, labels)
        else:
            return super().prediction_step(model, inputs, prediction_loss_only, ignore_keys=ignore_keys)
