import inspect
from functools import wraps
from os import PathLike
from pathlib import Path
from typing import Optional, Type, TypeVar, Union

from ._common import parser_context
from ._core import ArgumentParser
from ._loaders_dumpers import get_loader_exceptions, load_value
from ._optionals import _get_config_read_mode
from ._typehints import is_subclass_spec, resolve_class_path_by_name
from ._util import import_object

__all__ = ["FromConfigMixin"]

T = TypeVar("T")
OVERRIDE_KINDS = {inspect.Parameter.KEYWORD_ONLY, inspect.Parameter.POSITIONAL_OR_KEYWORD}


class FromConfigMixin:
    """Mixin class that adds from config support to classes.

    This mixin does two things:

        1. Adds support for overriding ``__init__`` defaults by defining a
           ``__from_config_init_defaults__`` class attribute pointing to a
           config file path. The overriding of defaults happens on subclass
           creation time. Inspecting the signature will give the overridden
           defaults.

        2. Adds a ``from_config`` ``@classmethod``, that instantiates the class
           based on a config file or dict.

    Attributes:
        ``__from_config_init_defaults__``: Optional path to a config file for
            overriding ``__init__`` defaults.
        ``__from_config_parser_kwargs__``: Additional kwargs to pass to the
            ArgumentParser used for parsing configs.
    """

    __from_config_init_defaults__: Optional[Union[str, PathLike]] = None
    __from_config_parser_kwargs__: dict = {}

    def __init_subclass__(cls, **kwargs) -> None:
        """Override ``__init__`` defaults for the subclass based on a config file."""
        super().__init_subclass__(**kwargs)
        _override_init_defaults(cls, cls.__from_config_parser_kwargs__)

    @classmethod
    def from_config(cls: Type[T], config: Union[str, PathLike, dict]) -> T:
        """Instantiate current class based on a config file or dict.

        Args:
            config: Path to a config file or a dict with config values.
        """
        kwargs, cls = _parse_class_kwargs_from_config(cls, config, **cls.__from_config_parser_kwargs__)  # type: ignore[attr-defined]
        return cls(**kwargs)


def _parse_class_kwargs_from_config(cls: Type[T], config: Union[str, PathLike, dict], **kwargs) -> tuple[dict, Type[T]]:
    """Parse the init kwargs for ``cls`` from a config file or dict."""
    parser = ArgumentParser(exit_on_error=False, **kwargs)
    if not isinstance(config, dict):
        from .typing import Path

        cfg_path = Path(config, mode=_get_config_read_mode())
        cfg_str = cfg_path.get_content()
        with parser_context(load_value_mode=parser.parser_mode):
            try:
                config = load_value(cfg_str, path=str(config))
            except get_loader_exceptions() as ex:
                raise TypeError(f"Problems parsing config '{config}': {ex}") from ex

    if not isinstance(config, dict):
        raise TypeError(f"Expected config to be a dict or parse into a dict: {config}")

    if is_subclass_spec(config):
        class_path = resolve_class_path_by_name(cls, config["class_path"])
        obj = import_object(class_path)
        if not issubclass(obj, cls):
            raise TypeError(f"Class '{class_path}' is not a subclass of '{cls.__name__}'")
        cls = obj
        config = {**config.get("init_args", {}), **config.get("dict_kwargs", {})}

    parser.add_class_arguments(cls)
    for required in parser.required_args:
        action = next((a for a in parser._actions if a.dest == required), None)
        action._required = False  # type: ignore[union-attr]
    parser.required_args.clear()
    cfg = parser.parse_object(config, defaults=False)
    return parser.instantiate_classes(cfg).as_dict(), cls


def _override_init_defaults(cls: Type[T], parser_kwargs: dict) -> None:
    """Override ``__init__`` defaults for ``cls`` based on ``__from_config_init_defaults__``."""
    config = getattr(cls, "__from_config_init_defaults__", None)
    if not isinstance(config, (str, PathLike, type(None))):
        raise TypeError("__from_config_init_defaults__ must be str, PathLike, or None")
    if not (isinstance(config, (str, PathLike)) and Path(config).is_file()):
        return

    defaults, cls = _parse_class_kwargs_from_config(cls, config, **parser_kwargs)
    _override_init_defaults_this_class(cls, defaults)
    _override_init_defaults_parent_classes(cls, defaults)


def _override_init_defaults_this_class(cls: Type[T], defaults: dict) -> None:
    params = inspect.signature(cls.__init__).parameters
    for name, default in defaults.copy().items():
        param = params.get(name)
        if param and param.kind in OVERRIDE_KINDS:
            if param.default == inspect._empty:
                raise TypeError(f"Overriding of required parameters not allowed: '{param.name}'")
            defaults.pop(name)
            if param.kind == inspect.Parameter.KEYWORD_ONLY:
                cls.__init__.__kwdefaults__[name] = default  # type: ignore[index]
            else:
                required = [p for p in params.values() if p.kind in OVERRIDE_KINDS and p.default == inspect._empty]
                index = list(params).index(name) - len(required)
                aux = cls.__init__.__defaults__ or ()
                cls.__init__.__defaults__ = aux[:index] + (default,) + aux[index + 1 :]


def _override_init_defaults_parent_classes(cls: Type[T], defaults: dict) -> None:
    # Gather defaults for parameters in parent classes' __init__
    override_parent_params = []
    for base in inspect.getmro(cls)[1:]:
        if not defaults:
            break

        params = inspect.signature(base.__init__).parameters  # type: ignore[misc]
        names = [name for name in defaults if name in params]
        for name in names:
            new_param = inspect.Parameter(
                name=name,
                kind=inspect.Parameter.KEYWORD_ONLY,
                default=defaults.pop(name),
                annotation=params[name].annotation,
            )
            override_parent_params.append(new_param)

    if not override_parent_params:
        return

    # Override defaults for parameters in parent classes' __init__ via a wrapper
    original_init = cls.__init__
    original_sig = inspect.signature(cls.__init__)
    parameters = list(original_sig.parameters.values())

    # Find and pop the **kwargs parameter, if it exists
    kwargs_param = None
    if parameters and parameters[-1].kind == inspect.Parameter.VAR_KEYWORD:
        kwargs_param = parameters.pop()

    # Add new parameters
    for param in override_parent_params:
        parameters.append(param)

    # Add **kwargs back at the end
    if kwargs_param:
        parameters.append(kwargs_param)

    # Create and set __init__ wrapper with new signature
    parent_defaults = {p.name: p.default for p in override_parent_params}

    @wraps(original_init)
    def wrapper(*args, **kwargs):
        for name, default in parent_defaults.items():
            if name not in kwargs:
                kwargs[name] = default
        return original_init(*args, **kwargs)

    wrapper.__signature__ = original_sig.replace(parameters=parameters)  # type: ignore[attr-defined]
    cls.__init__ = wrapper  # type: ignore[method-assign]