import logging
import random
import re
from collections import OrderedDict

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

from mmdet import datasets
from mmdet.core import (CocoDistEvalmAPHook, CocoDistEvalRecallHook,
                        DistEvalmAPHook, DistOptimizerHook, Fp16OptimizerHook)
from mmdet.datasets import DATASETS, build_dataloader
from mmdet.models import RPN


def get_root_logger(log_file=None, log_level=logging.INFO):
    logger = logging.getLogger('mmdet')
    # if the logger has been initialized, just return it
    if logger.hasHandlers():
        return logger

    logging.basicConfig(
        format='%(asctime)s - %(levelname)s - %(message)s', level=log_level)
    rank, _ = get_dist_info()
    if rank != 0:
        logger.setLevel('ERROR')
    elif log_file is not None:
        file_handler = logging.FileHandler(log_file, 'w')
        file_handler.setFormatter(
            logging.Formatter('%(asctime)s - %(levelname)s - %(message)s'))
        file_handler.setLevel(log_level)
        logger.addHandler(file_handler)

    return logger


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 parse_losses(losses):
    log_vars = OrderedDict()
    for loss_name, loss_value in losses.items():
        if isinstance(loss_value, torch.Tensor):
            log_vars[loss_name] = loss_value.mean()
        elif isinstance(loss_value, list):
            log_vars[loss_name] = sum(_loss.mean() for _loss in loss_value)
        else:
            raise TypeError(
                '{} is not a tensor or list of tensors'.format(loss_name))

    loss = sum(_value for _key, _value in log_vars.items() if 'loss' in _key)

    log_vars['loss'] = loss
    for loss_name, loss_value in log_vars.items():
        # reduce loss when distributed training
        if dist.is_available() and dist.is_initialized():
            loss_value = loss_value.data.clone()
            dist.all_reduce(loss_value.div_(dist.get_world_size()))
        log_vars[loss_name] = loss_value.item()

    return loss, log_vars


def batch_processor(model, data, train_mode):
    """Process a data batch.

    This method is required as an argument of Runner, which defines how to
    process a data batch and obtain proper outputs. The first 3 arguments of
    batch_processor are fixed.

    Args:
        model (nn.Module): A PyTorch model.
        data (dict): The data batch in a dict.
        train_mode (bool): Training mode or not. It may be useless for some
            models.

    Returns:
        dict: A dict containing losses and log vars.
    """
    losses = model(**data)
    loss, log_vars = parse_losses(losses)

    outputs = dict(
        loss=loss, log_vars=log_vars, num_samples=len(data['img'].data))

    return outputs


def train_detector(model,
                   dataset,
                   cfg,
                   distributed=False,
                   validate=False,
                   timestamp=None):
    logger = get_root_logger(cfg.log_level)

    # start training
    if distributed:
        _dist_train(
            model,
            dataset,
            cfg,
            validate=validate,
            logger=logger,
            timestamp=timestamp)
    else:
        _non_dist_train(
            model,
            dataset,
            cfg,
            validate=validate,
            logger=logger,
            timestamp=timestamp)


def build_optimizer(model, optimizer_cfg):
    """Build optimizer from configs.

    Args:
        model (:obj:`nn.Module`): The model with parameters to be optimized.
        optimizer_cfg (dict): The config dict of the optimizer.
            Positional fields are:
                - type: class name of the optimizer.
                - lr: base learning rate.
            Optional fields are:
                - any arguments of the corresponding optimizer type, e.g.,
                  weight_decay, momentum, etc.
                - paramwise_options: a dict with 3 accepted fileds
                  (bias_lr_mult, bias_decay_mult, norm_decay_mult).
                  `bias_lr_mult` and `bias_decay_mult` will be multiplied to
                  the lr and weight decay respectively for all bias parameters
                  (except for the normalization layers), and
                  `norm_decay_mult` will be multiplied to the weight decay
                  for all weight and bias parameters of normalization layers.

    Returns:
        torch.optim.Optimizer: The initialized optimizer.

    Example:
        >>> model = torch.nn.modules.Conv1d(1, 1, 1)
        >>> optimizer_cfg = dict(type='SGD', lr=0.01, momentum=0.9,
        >>>                      weight_decay=0.0001)
        >>> optimizer = build_optimizer(model, optimizer_cfg)
    """
    if hasattr(model, 'module'):
        model = model.module

    optimizer_cfg = optimizer_cfg.copy()
    paramwise_options = optimizer_cfg.pop('paramwise_options', None)
    # if no paramwise option is specified, just use the global setting
    if paramwise_options is None:
        return obj_from_dict(optimizer_cfg, torch.optim,
                             dict(params=model.parameters()))
    else:
        assert isinstance(paramwise_options, dict)
        # get base lr and weight decay
        base_lr = optimizer_cfg['lr']
        base_wd = optimizer_cfg.get('weight_decay', None)
        # weight_decay must be explicitly specified if mult is specified
        if ('bias_decay_mult' in paramwise_options
                or 'norm_decay_mult' in paramwise_options):
            assert base_wd is not None
        # get param-wise options
        bias_lr_mult = paramwise_options.get('bias_lr_mult', 1.)
        bias_decay_mult = paramwise_options.get('bias_decay_mult', 1.)
        norm_decay_mult = paramwise_options.get('norm_decay_mult', 1.)
        # set param-wise lr and weight decay
        params = []
        for name, param in model.named_parameters():
            param_group = {'params': [param]}
            if not param.requires_grad:
                # FP16 training needs to copy gradient/weight between master
                # weight copy and model weight, it is convenient to keep all
                # parameters here to align with model.parameters()
                params.append(param_group)
                continue

            # for norm layers, overwrite the weight decay of weight and bias
            # TODO: obtain the norm layer prefixes dynamically
            if re.search(r'(bn|gn)(\d+)?.(weight|bias)', name):
                if base_wd is not None:
                    param_group['weight_decay'] = base_wd * norm_decay_mult
            # for other layers, overwrite both lr and weight decay of bias
            elif name.endswith('.bias'):
                param_group['lr'] = base_lr * bias_lr_mult
                if base_wd is not None:
                    param_group['weight_decay'] = base_wd * bias_decay_mult
            # otherwise use the global settings

            params.append(param_group)

        optimizer_cls = getattr(torch.optim, optimizer_cfg.pop('type'))
        return optimizer_cls(params, **optimizer_cfg)


def _dist_train(model,
                dataset,
                cfg,
                validate=False,
                logger=None,
                timestamp=None):
    # prepare data loaders
    dataset = dataset if isinstance(dataset, (list, tuple)) else [dataset]
    data_loaders = [
        build_dataloader(
            ds, cfg.data.imgs_per_gpu, cfg.data.workers_per_gpu, dist=True)
        for ds in dataset
    ]
    # put model on gpus
    model = MMDistributedDataParallel(model.cuda())

    # build runner
    optimizer = build_optimizer(model, cfg.optimizer)
    runner = Runner(
        model, batch_processor, optimizer, cfg.work_dir, logger=logger)
    # 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)
    else:
        optimizer_config = DistOptimizerHook(**cfg.optimizer_config)

    # register hooks
    runner.register_training_hooks(cfg.lr_config, optimizer_config,
                                   cfg.checkpoint_config, cfg.log_config)
    runner.register_hook(DistSamplerSeedHook())
    # register eval hooks
    if validate:
        val_dataset_cfg = cfg.data.val
        eval_cfg = cfg.get('evaluation', {})
        if isinstance(model.module, RPN):
            # TODO: implement recall hooks for other datasets
            runner.register_hook(
                CocoDistEvalRecallHook(val_dataset_cfg, **eval_cfg))
        else:
            dataset_type = DATASETS.get(val_dataset_cfg.type)
            if issubclass(dataset_type, datasets.CocoDataset):
                runner.register_hook(
                    CocoDistEvalmAPHook(val_dataset_cfg, **eval_cfg))
            else:
                runner.register_hook(
                    DistEvalmAPHook(val_dataset_cfg, **eval_cfg))

    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, cfg.total_epochs)


def _non_dist_train(model,
                    dataset,
                    cfg,
                    validate=False,
                    logger=None,
                    timestamp=None):
    if validate:
        raise NotImplementedError('Built-in validation is not implemented '
                                  'yet in not-distributed training. Use '
                                  'distributed training or test.py and '
                                  '*eval.py scripts instead.')
    # prepare data loaders
    dataset = dataset if isinstance(dataset, (list, tuple)) else [dataset]
    data_loaders = [
        build_dataloader(
            ds,
            cfg.data.imgs_per_gpu,
            cfg.data.workers_per_gpu,
            cfg.gpus,
            dist=False) for ds in dataset
    ]
    # put model on gpus
    model = MMDataParallel(model, device_ids=range(cfg.gpus)).cuda()

    # build runner
    optimizer = build_optimizer(model, cfg.optimizer)
    runner = Runner(
        model, batch_processor, optimizer, cfg.work_dir, logger=logger)
    # 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=False)
    else:
        optimizer_config = cfg.optimizer_config
    runner.register_training_hooks(cfg.lr_config, optimizer_config,
                                   cfg.checkpoint_config, cfg.log_config)

    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, cfg.total_epochs)
