import warnings
from contextlib import contextmanager
from typing import Any, Callable, Dict, Iterator, List, Optional, Union

import torch
import torch.nn as nn
from torch.optim import Optimizer
from torch.optim.lr_scheduler import _LRScheduler as LRScheduler
from torch.utils.data import DataLoader

from colossalai.checkpoint_io import GeneralCheckpointIO
from colossalai.interface import ModelWrapper, OptimizerWrapper

from .accelerator import Accelerator
from .mixed_precision import MixedPrecision, mixed_precision_factory
from .plugin import Plugin
from .plugin.pp_plugin_base import PipelinePluginBase

__all__ = ['Booster']


class Booster:
    """
    Booster is a high-level API for training neural networks. It provides a unified interface for
    training with different precision, accelerator, and plugin.


    ```python
    # Following is pseudocode

    colossalai.launch(...)
    plugin = GeminiPlugin(...)
    booster = Booster(precision='fp16', plugin=plugin)

    model = GPT2()
    optimizer = HybridAdam(model.parameters())
    dataloader = plugin.prepare_dataloader(train_dataset, batch_size=8)
    lr_scheduler = LinearWarmupScheduler()
    criterion = GPTLMLoss()

    model, optimizer, criterion, dataloader, lr_scheduler = booster.boost(model, optimizer, criterion, dataloader, lr_scheduler)

    for epoch in range(max_epochs):
        for input_ids, attention_mask in dataloader:
            outputs = model(input_ids.cuda(), attention_mask.cuda())
            loss = criterion(outputs.logits, input_ids)
            booster.backward(loss, optimizer)
            optimizer.step()
            lr_scheduler.step()
            optimizer.zero_grad()
    ```

    Args:
        device (str or torch.device): The device to run the training. Default: None.
                                      If plugin is not used or plugin doesn't control the device,
                                      this argument will be set as training device ('cuda' will be used if argument is None).
        mixed_precision (str or MixedPrecision): The mixed precision to run the training. Default: None.
                                If the argument is a string, it can be 'fp16', 'fp16_apex', 'bf16', or 'fp8'.
                                'fp16' would use PyTorch AMP while `fp16_apex` would use Nvidia Apex.
        plugin (Plugin): The plugin to run the training. Default: None.
    """

    def __init__(self,
                 device: Optional[str] = None,
                 mixed_precision: Optional[Union[MixedPrecision, str]] = None,
                 plugin: Optional[Plugin] = None) -> None:
        if plugin is not None:
            assert isinstance(
                plugin, Plugin), f'Expected the argument plugin to be an instance of Plugin, but got {type(plugin)}.'
        self.plugin = plugin

        # set accelerator
        if self.plugin and self.plugin.control_device():
            self.accelerator = None
            if device is not None:
                warnings.warn('The plugin will control the accelerator, so the device argument will be ignored.')
        else:
            device = device or 'cuda'
            self.accelerator = Accelerator(device)

        # set precision
        if self.plugin and self.plugin.control_precision():
            if mixed_precision is not None:
                warnings.warn('The plugin will control the precision, so the mixed_precision argument will be ignored.')
            self.mixed_precision = None
        elif mixed_precision is None:
            self.mixed_precision = None
        else:
            # validate and set precision
            if isinstance(mixed_precision, str):
                # the user will take the default arguments for amp training
                self.mixed_precision = mixed_precision_factory(mixed_precision)
            elif isinstance(mixed_precision, MixedPrecision):
                # the user can customize the arguments by passing the precision object
                self.mixed_precision = mixed_precision
            else:
                raise ValueError(
                    f'Expected the argument mixed_precision to be a string or an instance of Precision, but got {type(mixed_precision)}.'
                )

        if self.plugin is not None and self.plugin.control_checkpoint_io():
            self.checkpoint_io = self.plugin.get_checkpoint_io()
        else:
            self.checkpoint_io = GeneralCheckpointIO()

    def boost(
        self,
        model: nn.Module,
        optimizer: Optional[Optimizer] = None,
        criterion: Optional[Callable] = None,
        dataloader: Optional[DataLoader] = None,
        lr_scheduler: Optional[LRScheduler] = None,
    ) -> List[Union[nn.Module, Optimizer, LRScheduler, DataLoader]]:
        """
        Wrap and inject features to the passed in model, optimizer, criterion, lr_scheduler, and dataloader.

        Args:
            model (nn.Module): Convert model into a wrapped model for distributive training.
                               The model might be decorated or partitioned by plugin's strategy after execution of this method.
            optimizer (Optimizer, optional): Convert optimizer into a wrapped optimizer for distributive training.
                                             The optimizer's param groups or states might be decorated or partitioned by plugin's strategy after execution of this method. Defaults to None.
            criterion (Callable, optional): The function that calculates loss. Defaults to None.
            dataloader (DataLoader, optional): The prepared dataloader for training. Defaults to None.
            lr_scheduler (LRScheduler, optional): The learning scheduler for training. Defaults to None.

        Returns:
            List[Union[nn.Module, Optimizer, LRScheduler, DataLoader]]: The list of boosted input arguments.
        """
        # TODO(FrankLeeeee): consider multi-model and multi-optimizer case
        # TODO(FrankLeeeee): consider multi-dataloader case
        # transform model for mixed precision
        if self.plugin:
            model, optimizer, criterion, dataloader, lr_scheduler = self.plugin.configure(
                model, optimizer, criterion, dataloader, lr_scheduler)

        if self.plugin and not self.plugin.control_device():
            # transform model for accelerator
            model = self.accelerator.configure(model)

        if self.mixed_precision and (self.plugin is None or self.plugin and not self.plugin.control_precision()):
            # transform model for mixed precision
            # when mixed_precision is specified and the plugin is not given or does not control the precision
            model, optimizer, criterion = self.mixed_precision.configure(model, optimizer, criterion)

        return model, optimizer, criterion, dataloader, lr_scheduler

    def backward(self, loss: torch.Tensor, optimizer: Optimizer) -> None:
        """Execution of backward during training step.

        Args:
            loss (torch.Tensor): The loss for backpropagation.
            optimizer (Optimizer): The optimizer to be updated.
        """
        # TODO(frank lee): implement this method with plugin
        optimizer.backward(loss)

    def execute_pipeline(self,
                         data_iter: Iterator,
                         model: nn.Module,
                         criterion: Callable[[Any, Any], torch.Tensor],
                         optimizer: Optional[Optimizer] = None,
                         return_loss: bool = True,
                         return_outputs: bool = False) -> Dict[str, Any]:
        """
        Execute forward & backward when utilizing pipeline parallel.
        Return loss or Huggingface style model outputs if needed.

        Warning: This function is tailored for the scenario of pipeline parallel.
        As a result, please don't do the forward/backward pass in the conventional way (model(input)/loss.backward())
        when doing pipeline parallel training with booster, which will cause unexpected errors.

        Args:
            data_iter(Iterator): The iterator for getting the next batch of data. Usually there are two ways to obtain this argument:
                                 1. wrap the dataloader to iterator through: iter(dataloader)
                                 2. get the next batch from dataloader, and wrap this batch to iterator: iter([batch])
            model (nn.Module): The model to execute forward/backward, it should be a model wrapped by a plugin that supports pipeline.
            criterion: (Callable[[Any, Any], torch.Tensor]): Criterion to be used. It should take two arguments: model outputs and inputs, and returns loss tensor.
                                                             'lambda y, x: loss_fn(y)' can turn a normal loss function into a valid two-argument criterion here.
            optimizer (Optimizer, optional): The optimizer for execution of backward. Can be None when only doing forward (i.e. evaluation). Defaults to None.
            return_loss (bool, optional): Whether to return loss in the dict returned by this method. Defaults to True.
            return_output (bool, optional): Whether to return Huggingface style model outputs in the dict returned by this method. Defaults to False.

        Returns:
            Dict[str, Any]: Output dict in the form of {'loss': ..., 'outputs': ...}.
                            ret_dict['loss'] is the loss of forward if return_loss is set to True, else None.
                            ret_dict['outputs'] is the Huggingface style model outputs during forward if return_output is set to True, else None.
        """
        assert isinstance(self.plugin,
                          PipelinePluginBase), f'The plugin {self.plugin.__class__.__name__} does not support pipeline.'
        return self.plugin.execute_pipeline(data_iter, model, criterion, optimizer, return_loss, return_outputs)

    def no_sync(self, model: nn.Module = None, optimizer: OptimizerWrapper = None) -> contextmanager:
        """Context manager to disable gradient synchronization across DP process groups.
           Support torch DDP and Low Level ZeRO-1 for now.

        Args:
            model (nn.Module): The model to be disabled gradient synchronization, for DDP
            optimizer (OptimizerWrapper): The optimizer to be disabled gradient synchronization, for ZeRO1-1

        Returns:
            contextmanager: Context to disable gradient synchronization.
        """
        assert self.plugin is not None, f'no_sync is only enabled when a plugin is provided and the plugin supports no_sync.'
        assert self.plugin.support_no_sync(), f'The plugin {self.plugin.__class__.__name__} does not support no_sync.'
        return self.plugin.no_sync(model, optimizer)

    def load_model(self, model: Union[nn.Module, ModelWrapper], checkpoint: str, strict: bool = True) -> None:
        """Load model from checkpoint.

        Args:
            model (nn.Module or ModelWrapper): A model boosted by Booster.
            checkpoint (str): Path to the checkpoint. It must be a local path.
                It should be a directory path if the checkpoint is sharded. Otherwise, it should be a file path.
            strict (bool, optional): whether to strictly enforce that the keys
                in :attr:`state_dict` match the keys returned by this module's
                :meth:`~torch.nn.Module.state_dict` function. Defaults to True.
        """
        self.checkpoint_io.load_model(model, checkpoint, strict)

    def save_model(self,
                   model: Union[nn.Module, ModelWrapper],
                   checkpoint: str,
                   shard: bool = False,
                   gather_dtensor: bool = True,
                   prefix: Optional[str] = None,
                   size_per_shard: int = 1024,
                   use_safetensors: bool = False) -> None:
        """Save model to checkpoint.

        Args:
            model (nn.Module or ModelWrapper): A model boosted by Booster.
            checkpoint (str): Path to the checkpoint. It must be a local path.
                It is a file path if ``shard=False``. Otherwise, it is a directory path.
            shard (bool, optional): Whether to save checkpoint a sharded way.
                If true, the checkpoint will be a folder with the same format as Huggingface transformers checkpoint. Otherwise, it will be a single file. Defaults to False.
            gather_dtensor (bool, optional): whether to gather the distributed tensor to the first device. Default: True.
            prefix (str, optional): A prefix added to parameter and buffer
                names to compose the keys in state_dict. Defaults to None.
            size_per_shard (int, optional): Maximum size of checkpoint shard file in MB. This is useful only when ``shard=True``. Defaults to 1024.
            use_safetensors (bool, optional): whether to use safe tensors. Default: False. If set to True, the checkpoint will be saved.
        """
        self.checkpoint_io.save_model(model,
                                      checkpoint=checkpoint,
                                      shard=shard,
                                      gather_dtensor=gather_dtensor,
                                      prefix=prefix,
                                      size_per_shard=size_per_shard,
                                      use_safetensors=use_safetensors)

    def load_optimizer(self, optimizer: Optimizer, checkpoint: str) -> None:
        """Load optimizer from checkpoint.

        Args:
            optimizer (Optimizer): An optimizer boosted by Booster.
            checkpoint (str): Path to the checkpoint. It must be a local path.
                It should be a directory path if the checkpoint is sharded. Otherwise, it should be a file path.
            prefix (str, optional): A prefix added to parameter and buffer
                names to compose the keys in state_dict. Defaults to None.
            size_per_shard (int, optional): Maximum size of checkpoint shard file in MB. This is useful only when ``shard=True``. Defaults to 1024.
        """
        self.checkpoint_io.load_optimizer(optimizer, checkpoint)

    def save_optimizer(self,
                       optimizer: Optimizer,
                       checkpoint: str,
                       shard: bool = False,
                       gather_dtensor: bool = True,
                       prefix: Optional[str] = None,
                       size_per_shard: int = 1024) -> None:
        """
        Save optimizer to checkpoint.

        Args:
            optimizer (Optimizer): An optimizer boosted by Booster.
            checkpoint (str): Path to the checkpoint. It must be a local path.
                It is a file path if ``shard=False``. Otherwise, it is a directory path.
            shard (bool, optional): Whether to save checkpoint a sharded way.
                If true, the checkpoint will be a folder. Otherwise, it will be a single file. Defaults to False.
            gather_dtensor (bool): whether to gather the distributed tensor to the first device. Default: True.
            prefix (str, optional): A prefix added to parameter and buffer
                names to compose the keys in state_dict. Defaults to None.
            size_per_shard (int, optional): Maximum size of checkpoint shard file in MB. This is useful only when ``shard=True``. Defaults to 1024.
        """
        self.checkpoint_io.save_optimizer(optimizer, checkpoint, shard, gather_dtensor, prefix, size_per_shard)

    def save_lr_scheduler(self, lr_scheduler: LRScheduler, checkpoint: str) -> None:
        """Save lr scheduler to checkpoint.

        Args:
            lr_scheduler (LRScheduler): A lr scheduler boosted by Booster.
            checkpoint (str): Path to the checkpoint. It must be a local file path.
        """
        self.checkpoint_io.save_lr_scheduler(lr_scheduler, checkpoint)

    def load_lr_scheduler(self, lr_scheduler: LRScheduler, checkpoint: str) -> None:
        """Load lr scheduler from checkpoint.

        Args:
            lr_scheduler (LRScheduler): A lr scheduler boosted by Booster.
            checkpoint (str): Path to the checkpoint. It must be a local file path.
        """
        self.checkpoint_io.load_lr_scheduler(lr_scheduler, checkpoint)
