import platform
import random
from functools import partial
from typing import Optional, Union

import numpy as np
from mmcv.parallel import collate
from mmcv.runner import get_dist_info
from mmcv.utils import Registry, build_from_cfg
from torch.utils.data import DataLoader
from torch.utils.data.dataset import Dataset

from .samplers import DistributedSampler

if platform.system() != 'Windows':
    # https://github.com/pytorch/pytorch/issues/973
    import resource
    rlimit = resource.getrlimit(resource.RLIMIT_NOFILE)
    base_soft_limit = rlimit[0]
    hard_limit = rlimit[1]
    soft_limit = min(max(4096, base_soft_limit), hard_limit)
    resource.setrlimit(resource.RLIMIT_NOFILE, (soft_limit, hard_limit))

DATASETS = Registry('dataset')
PIPELINES = Registry('pipeline')


def build_dataset(cfg: Union[dict, list, tuple],
                  default_args: Optional[Union[dict, None]] = None):
    """"Build dataset by the given config."""
    from .dataset_wrappers import (
        ConcatDataset,
        RepeatDataset,
    )
    if isinstance(cfg, (list, tuple)):
        dataset = ConcatDataset([build_dataset(c, default_args) for c in cfg])
    elif cfg['type'] == 'RepeatDataset':
        dataset = RepeatDataset(build_dataset(cfg['dataset'], default_args),
                                cfg['times'])
    else:
        dataset = build_from_cfg(cfg, DATASETS, default_args)

    return dataset


def build_dataloader(dataset: Dataset,
                     samples_per_gpu: int,
                     workers_per_gpu: int,
                     num_gpus: Optional[int] = 1,
                     dist: Optional[bool] = True,
                     shuffle: Optional[bool] = True,
                     round_up: Optional[bool] = True,
                     seed: Optional[Union[int, None]] = None,
                     persistent_workers: Optional[bool] = True,
                     **kwargs):
    """Build PyTorch DataLoader.

    In distributed training, each GPU/process has a dataloader.
    In non-distributed training, there is only one dataloader for all GPUs.

    Args:
        dataset (:obj:`Dataset`): A PyTorch dataset.
        samples_per_gpu (int): Number of training samples on each GPU, i.e.,
            batch size of each GPU.
        workers_per_gpu (int): How many subprocesses to use for data loading
            for each GPU.
        num_gpus (int, optional): Number of GPUs. Only used in non-distributed
            training.
        dist (bool, optional): Distributed training/test or not. Default: True.
        shuffle (bool, optional): Whether to shuffle the data at every epoch.
            Default: True.
        round_up (bool, optional): Whether to round up the length of dataset by
            adding extra samples to make it evenly divisible. Default: True.
        persistent_workers (bool): If True, the data loader will not shutdown
            the worker processes after a dataset has been consumed once.
            This allows to maintain the workers Dataset instances alive.
            The argument also has effect in PyTorch>=1.7.0.
            Default: True
        kwargs: any keyword argument to be used to initialize DataLoader

    Returns:
        DataLoader: A PyTorch dataloader.
    """
    rank, world_size = get_dist_info()
    if dist:
        sampler = DistributedSampler(dataset,
                                     world_size,
                                     rank,
                                     shuffle=shuffle,
                                     round_up=round_up)
        shuffle = False
        batch_size = samples_per_gpu
        num_workers = workers_per_gpu
    else:
        sampler = None
        batch_size = num_gpus * samples_per_gpu
        num_workers = num_gpus * workers_per_gpu

    init_fn = partial(
        worker_init_fn, num_workers=num_workers, rank=rank,
        seed=seed) if seed is not None else None

    data_loader = DataLoader(dataset,
                             batch_size=batch_size,
                             sampler=sampler,
                             num_workers=num_workers,
                             collate_fn=partial(
                                 collate, samples_per_gpu=samples_per_gpu),
                             pin_memory=False,
                             shuffle=shuffle,
                             worker_init_fn=init_fn,
                             persistent_workers=persistent_workers,
                             **kwargs)

    return data_loader


def worker_init_fn(worker_id: int, num_workers: int, rank: int, seed: int):
    """Init random seed for each worker."""
    # The seed of each worker equals to
    # num_worker * rank + worker_id + user_seed
    worker_seed = num_workers * rank + worker_id + seed
    np.random.seed(worker_seed)
    random.seed(worker_seed)