# Copyright (c) Open-MMLab. All rights reserved.
import os
import os.path as osp
import pkgutil
import time
import warnings
from collections import OrderedDict
from importlib import import_module

import torch
import torchvision
from torch.optim import Optimizer
from torch.utils import model_zoo

import mmcv
from ..fileio import load as load_file
from ..parallel import is_module_wrapper
from ..utils import mkdir_or_exist
from .dist_utils import get_dist_info

ENV_MMCV_HOME = 'MMCV_HOME'
ENV_XDG_CACHE_HOME = 'XDG_CACHE_HOME'
DEFAULT_CACHE_DIR = '~/.cache'


def _get_mmcv_home():
    mmcv_home = os.path.expanduser(
        os.getenv(
            ENV_MMCV_HOME,
            os.path.join(
                os.getenv(ENV_XDG_CACHE_HOME, DEFAULT_CACHE_DIR), 'mmcv')))

    mkdir_or_exist(mmcv_home)
    return mmcv_home


def load_state_dict(module, state_dict, strict=False, logger=None):
    """Load state_dict to a module.

    This method is modified from :meth:`torch.nn.Module.load_state_dict`.
    Default value for ``strict`` is set to ``False`` and the message for
    param mismatch will be shown even if strict is False.

    Args:
        module (Module): Module that receives the state_dict.
        state_dict (OrderedDict): Weights.
        strict (bool): 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. Default: ``False``.
        logger (:obj:`logging.Logger`, optional): Logger to log the error
            message. If not specified, print function will be used.
    """
    unexpected_keys = []
    all_missing_keys = []
    err_msg = []

    metadata = getattr(state_dict, '_metadata', None)
    state_dict = state_dict.copy()
    if metadata is not None:
        state_dict._metadata = metadata

    # use _load_from_state_dict to enable checkpoint version control
    def load(module, prefix=''):
        # recursively check parallel module in case that the model has a
        # complicated structure, e.g., nn.Module(nn.Module(DDP))
        if is_module_wrapper(module):
            module = module.module
        local_metadata = {} if metadata is None else metadata.get(
            prefix[:-1], {})
        module._load_from_state_dict(state_dict, prefix, local_metadata, True,
                                     all_missing_keys, unexpected_keys,
                                     err_msg)
        for name, child in module._modules.items():
            if child is not None:
                load(child, prefix + name + '.')

    load(module)
    load = None  # break load->load reference cycle

    # ignore "num_batches_tracked" of BN layers
    missing_keys = [
        key for key in all_missing_keys if 'num_batches_tracked' not in key
    ]

    if unexpected_keys:
        err_msg.append('unexpected key in source '
                       f'state_dict: {", ".join(unexpected_keys)}\n')
    if missing_keys:
        err_msg.append(
            f'missing keys in source state_dict: {", ".join(missing_keys)}\n')

    rank, _ = get_dist_info()
    if len(err_msg) > 0 and rank == 0:
        err_msg.insert(
            0, 'The model and loaded state dict do not match exactly\n')
        err_msg = '\n'.join(err_msg)
        if strict:
            raise RuntimeError(err_msg)
        elif logger is not None:
            logger.warning(err_msg)
        else:
            print(err_msg)


def load_url_dist(url, model_dir=None):
    """In distributed setting, this function only download checkpoint at local
    rank 0."""
    rank, world_size = get_dist_info()
    rank = int(os.environ.get('LOCAL_RANK', rank))
    if rank == 0:
        checkpoint = model_zoo.load_url(url, model_dir=model_dir)
    if world_size > 1:
        torch.distributed.barrier()
        if rank > 0:
            checkpoint = model_zoo.load_url(url, model_dir=model_dir)
    return checkpoint


def get_torchvision_models():
    model_urls = dict()
    for _, name, ispkg in pkgutil.walk_packages(torchvision.models.__path__):
        if ispkg:
            continue
        _zoo = import_module(f'torchvision.models.{name}')
        if hasattr(_zoo, 'model_urls'):
            _urls = getattr(_zoo, 'model_urls')
            model_urls.update(_urls)
    return model_urls


def get_external_models():
    mmcv_home = _get_mmcv_home()
    default_json_path = osp.join(mmcv.__path__[0], 'model_zoo/open_mmlab.json')
    default_urls = load_file(default_json_path)
    assert isinstance(default_urls, dict)
    external_json_path = osp.join(mmcv_home, 'open_mmlab.json')
    if osp.exists(external_json_path):
        external_urls = load_file(external_json_path)
        assert isinstance(external_urls, dict)
        default_urls.update(external_urls)

    return default_urls


def get_deprecated_model_names():
    deprecate_json_path = osp.join(mmcv.__path__[0],
                                   'model_zoo/deprecated.json')
    deprecate_urls = load_file(deprecate_json_path)
    assert isinstance(deprecate_urls, dict)

    return deprecate_urls


def _load_checkpoint(filename, map_location=None):
    """Load checkpoint from somewhere (modelzoo, file, url).

    Args:
        filename (str): Accept local filepath, URL, ``torchvision://xxx``,
            ``open-mmlab://xxx``. Please refer to ``docs/model_zoo.md`` for
            details.
        map_location (str | None): Same as :func:`torch.load`. Default: None.

    Returns:
        dict | OrderedDict: The loaded checkpoint. It can be either an
            OrderedDict storing model weights or a dict containing other
            information, which depends on the checkpoint.
    """
    if filename.startswith('modelzoo://'):
        warnings.warn('The URL scheme of "modelzoo://" is deprecated, please '
                      'use "torchvision://" instead')
        model_urls = get_torchvision_models()
        model_name = filename[11:]
        checkpoint = load_url_dist(model_urls[model_name])
    elif filename.startswith('torchvision://'):
        model_urls = get_torchvision_models()
        model_name = filename[14:]
        checkpoint = load_url_dist(model_urls[model_name])
    elif filename.startswith('open-mmlab://'):
        model_urls = get_external_models()
        model_name = filename[13:]
        deprecated_urls = get_deprecated_model_names()
        if model_name in deprecated_urls:
            warnings.warn(f'open-mmlab://{model_name} is deprecated in favor '
                          f'of open-mmlab://{deprecated_urls[model_name]}')
            model_name = deprecated_urls[model_name]
        model_url = model_urls[model_name]
        # check if is url
        if model_url.startswith(('http://', 'https://')):
            checkpoint = load_url_dist(model_url)
        else:
            filename = osp.join(_get_mmcv_home(), model_url)
            if not osp.isfile(filename):
                raise IOError(f'{filename} is not a checkpoint file')
            checkpoint = torch.load(filename, map_location=map_location)
    elif filename.startswith(('http://', 'https://')):
        checkpoint = load_url_dist(filename)
    else:
        if not osp.isfile(filename):
            raise IOError(f'{filename} is not a checkpoint file')
        checkpoint = torch.load(filename, map_location=map_location)
    return checkpoint


def load_checkpoint(model,
                    filename,
                    map_location=None,
                    strict=False,
                    logger=None):
    """Load checkpoint from a file or URI.

    Args:
        model (Module): Module to load checkpoint.
        filename (str): Accept local filepath, URL, ``torchvision://xxx``,
            ``open-mmlab://xxx``. Please refer to ``docs/model_zoo.md`` for
            details.
        map_location (str): Same as :func:`torch.load`.
        strict (bool): Whether to allow different params for the model and
            checkpoint.
        logger (:mod:`logging.Logger` or None): The logger for error message.

    Returns:
        dict or OrderedDict: The loaded checkpoint.
    """
    checkpoint = _load_checkpoint(filename, map_location)
    # OrderedDict is a subclass of dict
    if not isinstance(checkpoint, dict):
        raise RuntimeError(
            f'No state_dict found in checkpoint file {filename}')
    # get state_dict from checkpoint
    if 'state_dict' in checkpoint:
        state_dict = checkpoint['state_dict']
    else:
        state_dict = checkpoint
    # strip prefix of state_dict
    if list(state_dict.keys())[0].startswith('module.'):
        state_dict = {k[7:]: v for k, v in checkpoint['state_dict'].items()}
    # load state_dict
    load_state_dict(model, state_dict, strict, logger)
    return checkpoint


def weights_to_cpu(state_dict):
    """Copy a model state_dict to cpu.

    Args:
        state_dict (OrderedDict): Model weights on GPU.

    Returns:
        OrderedDict: Model weights on GPU.
    """
    state_dict_cpu = OrderedDict()
    for key, val in state_dict.items():
        state_dict_cpu[key] = val.cpu()
    return state_dict_cpu


def save_checkpoint(model, filename, optimizer=None, meta=None):
    """Save checkpoint to file.

    The checkpoint will have 3 fields: ``meta``, ``state_dict`` and
    ``optimizer``. By default ``meta`` will contain version and time info.

    Args:
        model (Module): Module whose params are to be saved.
        filename (str): Checkpoint filename.
        optimizer (:obj:`Optimizer`, optional): Optimizer to be saved.
        meta (dict, optional): Metadata to be saved in checkpoint.
    """
    if meta is None:
        meta = {}
    elif not isinstance(meta, dict):
        raise TypeError(f'meta must be a dict or None, but got {type(meta)}')
    meta.update(mmcv_version=mmcv.__version__, time=time.asctime())

    mmcv.mkdir_or_exist(osp.dirname(filename))
    if is_module_wrapper(model):
        model = model.module

    checkpoint = {
        'meta': meta,
        'state_dict': weights_to_cpu(model.state_dict())
    }
    # save optimizer state dict in the checkpoint
    if isinstance(optimizer, Optimizer):
        checkpoint['optimizer'] = optimizer.state_dict()
    elif isinstance(optimizer, dict):
        checkpoint['optimizer'] = {}
        for name, optim in optimizer.items():
            checkpoint['optimizer'][name] = optim.state_dict()
    # immediately flush buffer
    with open(filename, 'wb') as f:
        torch.save(checkpoint, f)
        f.flush()
