import inspect
import warnings
from functools import partial

from .misc import is_seq_of


class Registry:
    """A registry to map strings to classes.

    Args:
        name (str): Registry name.
    """

    def __init__(self, name):
        self._name = name
        self._module_dict = dict()

    def __len__(self):
        return len(self._module_dict)

    def __contains__(self, key):
        return self.get(key) is not None

    def __repr__(self):
        format_str = self.__class__.__name__ + \
                     f'(name={self._name}, ' \
                     f'items={self._module_dict})'
        return format_str

    @property
    def name(self):
        return self._name

    @property
    def module_dict(self):
        return self._module_dict

    def get(self, key):
        """Get the registry record.

        Args:
            key (str): The class name in string format.

        Returns:
            class: The corresponding class.
        """
        return self._module_dict.get(key, None)

    def _register_module(self, module_class, module_name=None, force=False):
        if not inspect.isclass(module_class):
            raise TypeError('module must be a class, '
                            f'but got {type(module_class)}')

        if module_name is None:
            module_name = module_class.__name__
        if isinstance(module_name, str):
            module_name = [module_name]
        else:
            assert is_seq_of(
                module_name,
                str), ('module_name should be either of None, an '
                       f'instance of str or list, but got {type(module_name)}')
        for name in module_name:
            if not force and name in self._module_dict:
                raise KeyError(f'{name} is already registered '
                               f'in {self.name}')
            self._module_dict[name] = module_class

    def deprecated_register_module(self, cls=None, force=False):
        warnings.warn(
            'The old API of register_module(module, force=False) '
            'is deprecated and will be removed, please use the new API '
            'register_module(name=None, force=False, module=None) instead.')
        if cls is None:
            return partial(self.deprecated_register_module, force=force)
        self._register_module(cls, force=force)
        return cls

    def register_module(self, name=None, force=False, module=None):
        """Register a module.

        A record will be added to `self._module_dict`, whose key is the class
        name or the specified name, and value is the class itself.
        It can be used as a decorator or a normal function.

        Example:
            >>> backbones = Registry('backbone')
            >>> @backbones.register_module()
            >>> class ResNet:
            >>>     pass

            >>> backbones = Registry('backbone')
            >>> @backbones.register_module(name='mnet')
            >>> class MobileNet:
            >>>     pass

            >>> backbones = Registry('backbone')
            >>> class ResNet:
            >>>     pass
            >>> backbones.register_module(ResNet)

        Args:
            name (str | None): The module name to be registered. If not
                specified, the class name will be used.
            force (bool, optional): Whether to override an existing class with
                the same name. Default: False.
            module (type): Module class to be registered.
        """
        if not isinstance(force, bool):
            raise TypeError(f'force must be a boolean, but got {type(force)}')
        # NOTE: This is a walkaround to be compatible with the old api,
        # while it may introduce unexpected bugs.
        if isinstance(name, type):
            return self.deprecated_register_module(name, force=force)

        # use it as a normal method: x.register_module(module=SomeClass)
        if module is not None:
            self._register_module(
                module_class=module, module_name=name, force=force)
            return module

        # raise the error ahead of time
        if not (name is None or isinstance(name, str)):
            raise TypeError(f'name must be a str, but got {type(name)}')

        # use it as a decorator: @x.register_module()
        def _register(cls):
            self._register_module(
                module_class=cls, module_name=name, force=force)
            return cls

        return _register


def build_from_cfg(cfg, registry, default_args=None):
    """Build a module from config dict.

    Args:
        cfg (dict): Config dict. It should at least contain the key "type".
        registry (:obj:`Registry`): The registry to search the type from.
        default_args (dict, optional): Default initialization arguments.

    Returns:
        object: The constructed object.
    """
    if not isinstance(cfg, dict):
        raise TypeError(f'cfg must be a dict, but got {type(cfg)}')
    if 'type' not in cfg:
        if default_args is None or 'type' not in default_args:
            raise KeyError(
                '`cfg` or `default_args` must contain the key "type", '
                f'but got {cfg}\n{default_args}')
    if not isinstance(registry, Registry):
        raise TypeError('registry must be an mmcv.Registry object, '
                        f'but got {type(registry)}')
    if not (isinstance(default_args, dict) or default_args is None):
        raise TypeError('default_args must be a dict or None, '
                        f'but got {type(default_args)}')

    args = cfg.copy()

    if default_args is not None:
        for name, value in default_args.items():
            args.setdefault(name, value)

    obj_type = args.pop('type')
    if isinstance(obj_type, str):
        obj_cls = registry.get(obj_type)
        if obj_cls is None:
            raise KeyError(
                f'{obj_type} is not in the {registry.name} registry')
    elif inspect.isclass(obj_type):
        obj_cls = obj_type
    else:
        raise TypeError(
            f'type must be a str or valid type, but got {type(obj_type)}')

    return obj_cls(**args)
