# Copyright (c) OpenMMLab. All rights reserved.
import random
import warnings

import numpy as np
import torch
import torch.distributed as dist
from mmcv.parallel import MMDataParallel, MMDistributedDataParallel
from mmcv.runner import (DistSamplerSeedHook, build_optimizer, build_runner,
                         get_dist_info)

from mmcls.core import DistOptimizerHook
from mmcls.datasets import build_dataloader, build_dataset
from mmcls.utils import get_root_logger

# TODO import eval hooks from mmcv and delete them from mmcls
try:
    from mmcv.runner.hooks import EvalHook, DistEvalHook
except ImportError:
    warnings.warn('DeprecationWarning: EvalHook and DistEvalHook from mmcls '
                  'will be deprecated.'
                  'Please install mmcv through master branch.')
    from mmcls.core import EvalHook, DistEvalHook

# TODO import optimizer hook from mmcv and delete them from mmcls
try:
    from mmcv.runner import Fp16OptimizerHook
except ImportError:
    warnings.warn('DeprecationWarning: FP16OptimizerHook from mmcls will be '
                  'deprecated. Please install mmcv>=1.1.4.')
    from mmcls.core import Fp16OptimizerHook


def init_random_seed(seed=None, device='cuda'):
    """Initialize random seed.

    If the seed is not set, the seed will be automatically randomized,
    and then broadcast to all processes to prevent some potential bugs.

    Args:
        seed (int, Optional): The seed. Default to None.
        device (str): The device where the seed will be put on.
            Default to 'cuda'.

    Returns:
        int: Seed to be used.
    """
    if seed is not None:
        return seed

    # Make sure all ranks share the same random seed to prevent
    # some potential bugs. Please refer to
    # https://github.com/open-mmlab/mmdetection/issues/6339
    rank, world_size = get_dist_info()
    seed = np.random.randint(2**31)
    if world_size == 1:
        return seed

    if rank == 0:
        random_num = torch.tensor(seed, dtype=torch.int32, device=device)
    else:
        random_num = torch.tensor(0, dtype=torch.int32, device=device)
    dist.broadcast(random_num, src=0)
    return random_num.item()


def set_random_seed(seed, deterministic=False):
    """Set random seed.

    Args:
        seed (int): Seed to be used.
        deterministic (bool): Whether to set the deterministic option for
            CUDNN backend, i.e., set `torch.backends.cudnn.deterministic`
            to True and `torch.backends.cudnn.benchmark` to False.
            Default: False.
    """
    random.seed(seed)
    np.random.seed(seed)
    torch.manual_seed(seed)
    torch.cuda.manual_seed_all(seed)
    if deterministic:
        torch.backends.cudnn.deterministic = True
        torch.backends.cudnn.benchmark = False


def train_model(model,
                dataset,
                cfg,
                distributed=False,
                validate=False,
                timestamp=None,
                device=None,
                meta=None):
    logger = get_root_logger()

    # prepare data loaders
    dataset = dataset if isinstance(dataset, (list, tuple)) else [dataset]

    sampler_cfg = cfg.data.get('sampler', None)

    data_loaders = [
        build_dataloader(
            ds,
            cfg.data.samples_per_gpu,
            cfg.data.workers_per_gpu,
            # cfg.gpus will be ignored if distributed
            num_gpus=len(cfg.gpu_ids),
            dist=distributed,
            round_up=True,
            seed=cfg.seed,
            sampler_cfg=sampler_cfg) for ds in dataset
    ]

    # put model on gpus
    if distributed:
        find_unused_parameters = cfg.get('find_unused_parameters', False)
        # Sets the `find_unused_parameters` parameter in
        # torch.nn.parallel.DistributedDataParallel
        model = MMDistributedDataParallel(
            model.cuda(),
            device_ids=[torch.cuda.current_device()],
            broadcast_buffers=False,
            find_unused_parameters=find_unused_parameters)
    else:
        if device == 'cpu':
            warnings.warn(
                'The argument `device` is deprecated. To use cpu to train, '
                'please refers to https://mmclassification.readthedocs.io/en'
                '/latest/getting_started.html#train-a-model')
            model = model.cpu()
        else:
            model = MMDataParallel(model, device_ids=cfg.gpu_ids)
            if not model.device_ids:
                from mmcv import digit_version, __version__
                assert digit_version(__version__) >= (1, 4, 4), \
                    'To train with CPU, please confirm your mmcv version ' \
                    'is not lower than v1.4.4'

    # build runner
    optimizer = build_optimizer(model, cfg.optimizer)

    if cfg.get('runner') is None:
        cfg.runner = {
            'type': 'EpochBasedRunner',
            'max_epochs': cfg.total_epochs
        }
        warnings.warn(
            'config is now expected to have a `runner` section, '
            'please set `runner` in your config.', UserWarning)

    runner = build_runner(
        cfg.runner,
        default_args=dict(
            model=model,
            batch_processor=None,
            optimizer=optimizer,
            work_dir=cfg.work_dir,
            logger=logger,
            meta=meta))

    # an ugly walkaround to make the .log and .log.json filenames the same
    runner.timestamp = timestamp

    # fp16 setting
    fp16_cfg = cfg.get('fp16', None)
    if fp16_cfg is not None:
        optimizer_config = Fp16OptimizerHook(
            **cfg.optimizer_config, **fp16_cfg, distributed=distributed)
    elif distributed and 'type' not in cfg.optimizer_config:
        optimizer_config = DistOptimizerHook(**cfg.optimizer_config)
    else:
        optimizer_config = cfg.optimizer_config

    # register hooks
    runner.register_training_hooks(
        cfg.lr_config,
        optimizer_config,
        cfg.checkpoint_config,
        cfg.log_config,
        cfg.get('momentum_config', None),
        custom_hooks_config=cfg.get('custom_hooks', None))
    if distributed and cfg.runner['type'] == 'EpochBasedRunner':
        runner.register_hook(DistSamplerSeedHook())

    # register eval hooks
    if validate:
        val_dataset = build_dataset(cfg.data.val, dict(test_mode=True))
        val_dataloader = build_dataloader(
            val_dataset,
            samples_per_gpu=cfg.data.samples_per_gpu,
            workers_per_gpu=cfg.data.workers_per_gpu,
            dist=distributed,
            shuffle=False,
            round_up=True)
        eval_cfg = cfg.get('evaluation', {})
        eval_cfg['by_epoch'] = cfg.runner['type'] != 'IterBasedRunner'
        eval_hook = DistEvalHook if distributed else EvalHook
        # `EvalHook` needs to be executed after `IterTimerHook`.
        # Otherwise, it will cause a bug if use `IterBasedRunner`.
        # Refers to https://github.com/open-mmlab/mmcv/issues/1261
        runner.register_hook(
            eval_hook(val_dataloader, **eval_cfg), priority='LOW')

    if cfg.resume_from:
        runner.resume(cfg.resume_from)
    elif cfg.load_from:
        runner.load_checkpoint(cfg.load_from)
    runner.run(data_loaders, cfg.workflow)
