from typing import Callable, Iterator, List, Optional, Tuple

import torch.nn as nn
from torch.nn.parallel import DistributedDataParallel as DDP
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 CheckpointIO, GeneralCheckpointIO
from colossalai.cluster import DistCoordinator
from colossalai.interface import ModelWrapper, OptimizerWrapper

from .dp_plugin_base import DPPluginBase

__all__ = ["TorchDDPPlugin"]


class TorchDDPCheckpointIO(GeneralCheckpointIO):
    def __init__(self) -> None:
        super().__init__()
        self.coordinator = DistCoordinator()

    def load_unsharded_model(self, model: ModelWrapper, checkpoint: str, strict: bool = True):
        """
        Load model from checkpoint.
        """
        assert isinstance(model, ModelWrapper), "Please boost the model before loading!"
        super().load_unsharded_model(model.unwrap(), checkpoint, strict=strict)

    def save_unsharded_model(self, model: ModelWrapper, checkpoint: str, gather_dtensor: bool, use_safetensors: bool):
        """
        Save model to checkpoint but only on master process.
        """
        assert isinstance(model, ModelWrapper), "Please boost the model before saving!"
        if self.coordinator.is_master():
            super().save_unsharded_model(model.unwrap(), checkpoint, gather_dtensor, use_safetensors)

    def load_unsharded_optimizer(self, optimizer: OptimizerWrapper, checkpoint: str):
        """
        Load optimizer from checkpoint.
        """
        assert isinstance(optimizer, OptimizerWrapper), "Please boost the optimizer before loading!"
        super().load_unsharded_optimizer(optimizer, checkpoint)

    def save_unsharded_optimizer(self, optimizer: OptimizerWrapper, checkpoint: str, gather_dtensor: bool):
        """
        Save optimizer to checkpoint but only on master process.
        """
        assert isinstance(optimizer, OptimizerWrapper), "Please boost the optimizer before saving!"
        if self.coordinator.is_master():
            super().save_unsharded_optimizer(optimizer, checkpoint, gather_dtensor)

    def save_lr_scheduler(self, lr_scheduler: LRScheduler, checkpoint: str):
        """
        Save model to checkpoint but only on master process.
        """
        if self.coordinator.is_master():
            super().save_lr_scheduler(lr_scheduler, checkpoint)

    def save_sharded_model(
        self,
        model: ModelWrapper,
        checkpoint_path: str,
        gather_dtensor: bool = True,
        prefix: Optional[str] = None,
        max_shard_size: int = 1024,
        use_safetensors: bool = False,
    ):
        """
        Save model to checkpoint but only on master process.
        """
        assert isinstance(model, ModelWrapper), "Please boost the model before saving!"
        if self.coordinator.is_master():
            super().save_sharded_model(
                model.unwrap(), checkpoint_path, gather_dtensor, prefix, max_shard_size, use_safetensors
            )

    def load_sharded_model(
        self,
        model: ModelWrapper,
        checkpoint_index_file: str,
        strict: bool = False,
        use_safetensors: bool = False,
        load_sub_module: bool = True,
    ):
        """
        Load model from sharded checkpoint.
        """
        assert isinstance(model, ModelWrapper), "Please boost the model before loading!"
        super().load_sharded_model(model.unwrap(), checkpoint_index_file, strict, use_safetensors, load_sub_module)

    def save_sharded_optimizer(
        self,
        optimizer: OptimizerWrapper,
        checkpoint: str,
        gather_dtensor: bool = True,
        prefix: Optional[str] = None,
        size_per_shard: int = 1024,
    ):
        """
        Save optimizer to sharded checkpoint but only on master process.
        """
        assert isinstance(optimizer, OptimizerWrapper), "Please boost the optimizer before saving!"
        if self.coordinator.is_master():
            super().save_sharded_optimizer(optimizer.unwrap(), checkpoint, gather_dtensor, prefix, size_per_shard)

    def load_sharded_optimizer(
        self,
        optimizer: Optimizer,
        index_file_path: str,
        prefix: Optional[str] = None,
    ):
        """
        Load optimizer from sharded checkpoint.
        """
        assert isinstance(optimizer, OptimizerWrapper), "Please boost the optimizer before loading!"
        super().load_sharded_optimizer(optimizer.unwrap(), index_file_path, prefix)


class TorchDDPModel(ModelWrapper):
    def __init__(self, module: nn.Module, *args, **kwargs) -> None:
        super().__init__(module)
        self.module = DDP(module, *args, **kwargs)

    def unwrap(self):
        return self.module.module


class TorchDDPPlugin(DPPluginBase):
    """
    Plugin for PyTorch DDP.

    ```python
    from colossalai.booster import Booster
    from colossalai.booster.plugin import TorchDDPPlugin

    model, train_dataset, optimizer, criterion = ...
    plugin = TorchDDPPlugin()

    train_dataloader = plugin.prepare_dataloader(train_dataset, batch_size=8)
    booster = Booster(plugin=plugin)
    model, optimizer, train_dataloader, criterion = booster.boost(model, optimizer, train_dataloader, criterion)
    ```

    Args:
        broadcast_buffers (bool, optional): Whether to broadcast buffers in the beginning of training. Defaults to True.
        bucket_cap_mb (int, optional): The bucket size in MB. Defaults to 25.
        find_unused_parameters (bool, optional): Whether to find unused parameters. Defaults to False.
        check_reduction (bool, optional): Whether to check reduction. Defaults to False.
        gradient_as_bucket_view (bool, optional): Whether to use gradient as bucket view. Defaults to False.
        static_graph (bool, optional): Whether to use static graph. Defaults to False.
    """

    def __init__(
        self,
        broadcast_buffers: bool = True,
        bucket_cap_mb: int = 25,
        find_unused_parameters: bool = False,
        check_reduction: bool = False,
        gradient_as_bucket_view: bool = False,
        static_graph: bool = False,
    ) -> None:
        super().__init__()
        self.ddp_kwargs = dict(
            broadcast_buffers=broadcast_buffers,
            bucket_cap_mb=bucket_cap_mb,
            find_unused_parameters=find_unused_parameters,
            check_reduction=check_reduction,
            gradient_as_bucket_view=gradient_as_bucket_view,
            static_graph=static_graph,
        )

    def support_no_sync(self) -> bool:
        return True

    def control_precision(self) -> bool:
        return False

    def supported_precisions(self) -> List[str]:
        return ["fp16", "fp16_apex", "bf16", "fp8"]

    def control_device(self) -> bool:
        return True

    def supported_devices(self) -> List[str]:
        return ["cuda"]

    def configure(
        self,
        model: nn.Module,
        optimizer: Optional[Optimizer] = None,
        criterion: Optional[Callable] = None,
        dataloader: Optional[DataLoader] = None,
        lr_scheduler: Optional[LRScheduler] = None,
    ) -> Tuple[nn.Module, OptimizerWrapper, Callable, DataLoader, LRScheduler]:
        # cast model to cuda
        model = model.cuda()

        # convert model to sync bn
        model = nn.SyncBatchNorm.convert_sync_batchnorm(model, None)

        # wrap the model with PyTorch DDP
        model = TorchDDPModel(model, **self.ddp_kwargs)

        if optimizer is not None and not isinstance(optimizer, OptimizerWrapper):
            optimizer = OptimizerWrapper(optimizer)

        return model, optimizer, criterion, dataloader, lr_scheduler

    def control_checkpoint_io(self) -> bool:
        return True

    def get_checkpoint_io(self) -> CheckpointIO:
        return TorchDDPCheckpointIO()

    def no_sync(self, model: nn.Module, optimizer: OptimizerWrapper) -> Iterator[None]:
        assert isinstance(model, TorchDDPModel), "Model is not boosted by TorchDDPPlugin."
        return model.module.no_sync()
