from __future__ import annotations

import copy
import gzip
import json
import logging
from collections.abc import Callable
from datetime import date, datetime
from functools import wraps
from pathlib import Path
from typing import Any, TypeVar, cast

T = TypeVar("T", bound="ComplexSerializableType")
TCallable = TypeVar("TCallable", bound=Callable[..., Any])

logger = logging.getLogger(__name__)


class SerializationError(Exception):
    pass


class ComplexSerializableType:
    """
    A class that can be serialized to json and thus a dictionary.

    Direct inheritance from this class is required for the class to be serializable.
    Only the `serialized_attributes` are serialized. If `__slots__` is defined, only those attributes are serialized.

    .. note::
        The `to_dict` and `from_dict` should be overridden if non-trivial types of attributes need to be serialized.
    """

    __slots__: tuple[str]

    def __init__(self, *args, **kwargs):
        pass

    @property
    def serialized_attributes(self) -> list[str]:
        if hasattr(self, "__slots__") and self.__slots__:
            return list(self.__slots__)
        return list(self.__dict__.keys())

    def to_dict(self) -> dict[str, Any]:
        if hasattr(self, "__slots__") and self.__slots__:
            return {
                key: copy.deepcopy(getattr(self, key)) for key in self.__slots__ if key in self.serialized_attributes
            }
        return {key: val for key, val in copy.deepcopy(self.__dict__).items() if key in self.serialized_attributes}

    @classmethod
    def from_dict(cls: type[T], dct: dict) -> T:
        try:
            return cls(**dct)
        except TypeError as e:
            raise TypeError(f"Dict: {dct} on {cls.__mro__}") from e

    def to_json(self, output_path: str | Path | None = None, compress: bool = False) -> None:
        """
        Serializes `ComplexSerializableType` instance to json file.
        :param str | Path | None output_path: path where the file will be stored. If None, `obj.json_path` access is attempted, defaults to None
        :param bool compress: if True, will be compressed with gzip, defaults to False
        """
        if not output_path and (not hasattr(self, "json_path") or not self.json_path):  # type: ignore
            raise SerializationError(
                f"The object {self} of type {get_class_fullname(self)} does not have json_path attribute set but to_json() was called without an argument."
            )
        if not output_path:
            output_path = self.json_path  # type: ignore
            if self.json_path is None:  # type: ignore
                raise SerializationError(f"json_path attribute for {get_class_fullname(self)} was not yet set.")
            if hasattr(self, "root_dir") and self.root_dir is None:  # type: ignore
                raise SerializationError(f"root_dir attribute for {get_class_fullname(self)} was not yet set.")

        if not output_path:
            raise SerializationError("Output path for json must be set.")

        path = Path(output_path)
        if path.is_dir():
            raise SerializationError("Output path for json cannot be a directory.")

        if compress:
            if path.suffix != ".gz":
                raise SerializationError(f"Expected path to a compressed file (.gz), got {path.suffix}.")

            with gzip.open(path, "wt", encoding="utf-8") as handle:
                json.dump(self, handle, indent=4, cls=CustomJSONEncoder, ensure_ascii=False)  # type: ignore
        else:
            if path.suffix != ".json":
                raise SerializationError(f"Expected path to a json file (.json), got {path.suffix}.")

            with path.open("wt") as handle:
                json.dump(self, handle, indent=4, cls=CustomJSONEncoder, ensure_ascii=False)  # type: ignore

    @classmethod
    def from_json(cls: type[T], input_path: str | Path, is_compressed: bool = False) -> T:
        """
        Will load `ComplexSerializableType` from json.
        :param str | Path input_path: path to load the file from
        :param bool is_compressed: if True, will decompress .gz first, defaults to False
        :return T: the deserialized object
        """
        path = Path(input_path)
        if is_compressed:
            if path.suffix != ".gz":
                raise SerializationError(f"Expected path to a compressed file (.gz), got {path.suffix}.")

            with gzip.open(path, "rt", encoding="utf-8") as handle:
                return json.load(handle, cls=CustomJSONDecoder)
        else:
            if path.suffix != ".json":
                raise SerializationError(f"Expected path to a json file (.json), got {path.suffix}.")

            with path.open("r") as handle:
                return json.load(handle, cls=CustomJSONDecoder)


def serialize(func: Callable) -> Callable:
    """
    Decorator to be used on instance methods of ComplexSerializableType child classes.
    The decorated method will be serialized to json after execution.

    Adds the `update_json` keyword argument to the decorated method. If set to False, the json will not be updated.
    """

    @wraps(func)
    def _serialize(*args, **kwargs):
        if not args or not issubclass(type(args[0]), ComplexSerializableType):
            raise ValueError(
                "@serialize decorator is to be used only on instance methods of ComplexSerializableType child classes."
            )

        if hasattr(args[0], "root_dir") and args[0].root_dir is None:
            raise SerializationError(
                "The invoked method requires dataset serialization. Cannot serialize without root_dir set. You can set it with obj.root_dir = ..."
            )

        update_json = kwargs.pop("update_json", True)
        result = func(*args, **kwargs)
        if update_json:
            args[0].to_json()
        return result

    return _serialize


def only_backed(throw: bool = True):
    """
    Decorator to be used on instance methods of ComplexSerializableType child classes.
    The decorated method will only be executed if the `root_dir` attribute is set.

    :param bool throw: if True, will raise ValueError if `root_dir` is not set, defaults to True
                       Otherwise, just logs a warning and returns None.
    """

    def deco(func: TCallable) -> TCallable:
        @wraps(func)
        def _only_backed(*args, **kwargs):
            if args[0].root_dir is None:
                if throw:
                    raise ValueError(f"Method {func.__name__} can only be called on backed dataset.")
                else:
                    logger.warning(f"Method {func.__name__} can only be called on backed dataset.")
                    return None
            else:
                return func(*args, **kwargs)

        return cast(TCallable, _only_backed)

    return deco


def get_class_fullname(obj: Any) -> str:
    """
    Returns the full name of the class of the object.

    Example:
    >>> get_class_fullname(datetime.now())
    'datetime.datetime'


    :param Any obj: object to get the class name from
    :return str: full name of the class
    """
    klass = obj if isinstance(obj, type) else obj.__class__
    module = klass.__module__
    if module == "builtins":
        return klass.__qualname__
    return module + "." + klass.__qualname__


class CustomJSONEncoder(json.JSONEncoder):
    """
    Custom JSONEncoder.
    """

    def default(self, obj):
        if isinstance(obj, ComplexSerializableType):
            return {**{"_type": get_class_fullname(obj)}, **obj.to_dict()}
        if isinstance(obj, dict):
            return obj
        if isinstance(obj, set):
            return {"_type": "Set", "elements": sorted(obj)}
        if isinstance(obj, frozenset):
            return sorted(obj)
        if isinstance(obj, date):
            return str(obj)
        if isinstance(obj, datetime):
            return obj.isoformat()
        if isinstance(obj, Path):
            return str(obj)
        return super().default(obj)


class CustomJSONDecoder(json.JSONDecoder):
    """
    Custom JSONDecoder.

    Any complex object that should be de-serializable must inherit directly from class
    `ComplexSerializableType` (nested inheritance does not currently work (because x.__subclassess__() prints only direct
    subclasses. Any such class must implement methods to_dict() and from_dict(). These are used to drive serialization.
    """

    def __init__(self, *args, **kwargs):
        json.JSONDecoder.__init__(self, object_hook=self.object_hook, *args, **kwargs)
        self.serializable_complex_types = {get_class_fullname(x): x for x in ComplexSerializableType.__subclasses__()}

    def object_hook(self, obj):
        if "_type" in obj and obj["_type"] == "Set":
            return set(obj["elements"])
        if "_type" in obj and obj["_type"] in self.serializable_complex_types:
            complex_type = obj.pop("_type")
            return self.serializable_complex_types[complex_type].from_dict(obj)
        if "_type" in obj:
            raise SerializationError(f"JSONDecoder doesn't know how to handle {obj}")

        return obj