#
# Copyright (c) 2022-2023, NVIDIA CORPORATION.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#


import importlib
import traceback

from contextlib import contextmanager
from cuml.internals.device_support import CPU_ENABLED, GPU_ENABLED
from cuml.internals import logger


class UnavailableError(Exception):
    """Error thrown if a symbol is unavailable due to an issue importing it"""


def return_false(*args, **kwargs):
    """A placeholder function that always returns False"""
    return False


@contextmanager
def null_decorator(*args, **kwargs):
    if len(kwargs) == 0 and len(args) == 1 and callable(args[0]):
        return args[0]
    else:

        def inner(func):
            return func

        return inner


class UnavailableMeta(type):
    """A metaclass for generating placeholder objects for unavailable symbols

    This metaclass allows errors to be deferred from import time to the time
    that a symbol is actually used in order to streamline the usage of optional
    dependencies. This is particularly useful for attempted imports of GPU-only
    modules which will only be invoked if GPU-only functionality is
    specifically used.

    If an attempt to import a symbol fails, this metaclass is used to generate
    a class which stands in for that symbol. Any attempt to call the symbol
    (instantiate the class) or access its attributes will throw an
    UnavailableError exception. Furthermore, this class can be used in
    e.g. isinstance checks, since it will (correctly) fail to match any
    instance it is compared against.

    In addition to calls and attribute access, a number of dunder methods are
    implemented so that other common usages of imported symbols (e.g.
    arithmetic) throw an UnavailableError, but this is not guaranteed for
    all possible uses. In such cases, other exception types (typically
    TypeErrors) will be thrown instead.
    """

    def __new__(meta, name, bases, dct):
        if dct.get("_msg", None) is None:
            dct["_msg"] = f"{name} could not be imported"
        name = f"MISSING{name}"
        return super(UnavailableMeta, meta).__new__(meta, name, bases, dct)

    def __call__(cls, *args, **kwargs):
        raise UnavailableError(cls._msg)

    def __getattr__(cls, name):
        raise UnavailableError(cls._msg)

    def __eq__(cls, other):
        raise UnavailableError(cls._msg)

    def __lt__(cls, other):
        raise UnavailableError(cls._msg)

    def __gt__(cls, other):
        raise UnavailableError(cls._msg)

    def __ne__(cls, other):
        raise UnavailableError(cls._msg)

    def __abs__(cls, other):
        raise UnavailableError(cls._msg)

    def __add__(cls, other):
        raise UnavailableError(cls._msg)

    def __radd__(cls, other):
        raise UnavailableError(cls._msg)

    def __iadd__(cls, other):
        raise UnavailableError(cls._msg)

    def __floordiv__(cls, other):
        raise UnavailableError(cls._msg)

    def __rfloordiv__(cls, other):
        raise UnavailableError(cls._msg)

    def __ifloordiv__(cls, other):
        raise UnavailableError(cls._msg)

    def __lshift__(cls, other):
        raise UnavailableError(cls._msg)

    def __rlshift__(cls, other):
        raise UnavailableError(cls._msg)

    def __mul__(cls, other):
        raise UnavailableError(cls._msg)

    def __rmul__(cls, other):
        raise UnavailableError(cls._msg)

    def __imul__(cls, other):
        raise UnavailableError(cls._msg)

    def __ilshift__(cls, other):
        raise UnavailableError(cls._msg)

    def __pow__(cls, other):
        raise UnavailableError(cls._msg)

    def __rpow__(cls, other):
        raise UnavailableError(cls._msg)

    def __ipow__(cls, other):
        raise UnavailableError(cls._msg)

    def __rshift__(cls, other):
        raise UnavailableError(cls._msg)

    def __rrshift__(cls, other):
        raise UnavailableError(cls._msg)

    def __irshift__(cls, other):
        raise UnavailableError(cls._msg)

    def __sub__(cls, other):
        raise UnavailableError(cls._msg)

    def __rsub__(cls, other):
        raise UnavailableError(cls._msg)

    def __isub__(cls, other):
        raise UnavailableError(cls._msg)

    def __truediv__(cls, other):
        raise UnavailableError(cls._msg)

    def __rtruediv__(cls, other):
        raise UnavailableError(cls._msg)

    def __itruediv__(cls, other):
        raise UnavailableError(cls._msg)

    def __divmod__(cls, other):
        raise UnavailableError(cls._msg)

    def __rdivmod__(cls, other):
        raise UnavailableError(cls._msg)

    def __neg__(cls):
        raise UnavailableError(cls._msg)

    def __invert__(cls):
        raise UnavailableError(cls._msg)

    def __hash__(cls):
        raise UnavailableError(cls._msg)

    def __index__(cls):
        raise UnavailableError(cls._msg)

    def __iter__(cls):
        raise UnavailableError(cls._msg)

    def __delitem__(cls, name):
        raise UnavailableError(cls._msg)

    def __setitem__(cls, name, value):
        raise UnavailableError(cls._msg)

    def __enter__(cls, *args, **kwargs):
        raise UnavailableError(cls._msg)

    def __get__(cls, *args, **kwargs):
        raise UnavailableError(cls._msg)

    def __delete__(cls, *args, **kwargs):
        raise UnavailableError(cls._msg)

    def __len__(cls):
        raise UnavailableError(cls._msg)


def is_unavailable(obj):
    """Helper to check if given symbol is actually a placeholder"""
    return type(obj) is UnavailableMeta


class UnavailableNullContext:
    """A placeholder class for unavailable context managers

    This context manager will return a value which will throw an
    UnavailableError if used in any way, but the context manager itself can be
    safely invoked.
    """

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

    def __enter__(self):
        return UnavailableMeta(
            "MissingContextValue",
            (),
            {
                "_msg": "Attempted to make use of placeholder context return value."
            },
        )

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


def safe_import(module, *, msg=None, alt=None):
    """A function used to import modules that may not be available

    This function will attempt to import a module with the given name, but it
    will not throw an ImportError if the module is not found. Instead, it will
    return a placeholder object which will raise an exception only if used.

    Parameters
    ----------
    module: str
        The name of the module to import.
    msg: str or None
        An optional error message to be displayed if this module is used
        after a failed import.
    alt: object
        An optional module to be used in place of the given module if it
        fails to import

    Returns
    -------
    object
        The imported module, the given alternate, or a class derived from
        UnavailableMeta.
    """
    try:
        return importlib.import_module(module)
    except ImportError:
        exception_text = traceback.format_exc()
        logger.debug(f"Import of {module} failed with: {exception_text}")
    except Exception:
        exception_text = traceback.format_exc()
        logger.info(f"Import of {module} failed with: {exception_text}")
    if msg is None:
        msg = f"{module} could not be imported"
    if alt is None:
        return UnavailableMeta(module.rsplit(".")[-1], (), {"_msg": msg})
    else:
        return alt


def safe_import_from(module, symbol, *, msg=None, alt=None):
    """A function used to import symbols from modules that may not be available

    This function will attempt to import a symbol with the given name from
    the given module, but it will not throw an ImportError if the symbol is not
    found. Instead, it will return a placeholder object which will raise an
    exception only if used.

    Parameters
    ----------
    module: str
        The name of the module in which the symbol is defined.
    symbol: str
        The name of the symbol to import.
    msg: str or None
        An optional error message to be displayed if this symbol is used
        after a failed import.
    alt: object
        An optional object to be used in place of the given symbol if it fails
        to import

    Returns
    -------
    object
        The imported symbol, the given alternate, or a class derived from
        UnavailableMeta.
    """
    try:
        imported_module = importlib.import_module(module)
        return getattr(imported_module, symbol)
    except ImportError:
        exception_text = traceback.format_exc()
        logger.debug(f"Import of {module} failed with: {exception_text}")
    except AttributeError:
        exception_text = traceback.format_exc()
        logger.debug(
            f"Import of {symbol} from {module} failed with: {exception_text}"
        )
    except Exception:
        exception_text = traceback.format_exc()
        logger.info(
            f"Import of {module}.{symbol} failed with: {exception_text}"
        )
    if msg is None:
        msg = f"{module}.{symbol} could not be imported"
    if alt is None:
        return UnavailableMeta(symbol, (), {"_msg": msg})
    else:
        return alt


def gpu_only_import(module, *, alt=None):
    """A function used to import modules required only in GPU installs

    This function will attempt to import a module with the given name, but it
    will only throw an ImportError if the attempt fails AND this is not a
    CPU-only build. This allows GPU-only dependencies to be cleanly
    imported in CPU-only builds but guarantees that the correct exception
    will be raised if a required dependency is unavailable. If the import
    fails on a CPU-only build and no alternate module is indicated via the
    keyword `alt` argument, a placeholder object will be returned which raises
    an exception only if used.

    Parameters
    ----------
    module: str
        The name of the module to import.
    alt: object
        An optional module to be used in place of the given module if it
        fails to import in a non-GPU-enabled install

    Returns
    -------
    object
        The imported module, the given alternate, or a class derived from
        UnavailableMeta.
    """
    if GPU_ENABLED:
        return importlib.import_module(module)
    else:
        return safe_import(
            module,
            msg=f"{module} is not installed in non GPU-enabled installations",
            alt=alt,
        )


def gpu_only_import_from(module, symbol, *, alt=None):
    """A function used to import symbols required only in GPU installs

    This function will attempt to import a symbol from a module with the given
    names, but it will only throw an ImportError if the attempt fails AND this
    is not a CPU-only build. This allows GPU-only dependencies to be cleanly
    imported in CPU-only builds but guarantees that the correct exception will
    be raised if a required dependency is unavailable. If the import fails on a
    CPU-only build and no alternate module is indicated via the keyword `alt`
    argument, a placeholder object will be returned which raises an exception
    only if used.

    Parameters
    ----------
    module: str
        The name of the module to import.
    symbol: str
        The name of the symbol to import.
    alt: object
        An optional object to be used in place of the given symbol if it fails
        to import in a non-GPU-enabled install

    Returns
    -------
    object
        The imported symbol, the given alternate, or a class derived from
        UnavailableMeta.
    """
    if GPU_ENABLED:
        imported_module = importlib.import_module(module)
        return getattr(imported_module, symbol)
    else:
        return safe_import_from(
            module,
            symbol,
            msg=f"{module}.{symbol} is not available in CPU-only"
            " installations",
            alt=alt,
        )


def cpu_only_import(module, *, alt=None):
    """A function used to import modules required only in CPU installs

    This function will attempt to import a module with the given name, but it
    will only throw an ImportError if the attempt fails AND this is not a
    GPU-only build. This allows CPU-only dependencies to be cleanly
    imported in GPU-only builds but guarantees that the correct exception
    will be raised if a required dependency is unavailable. If the import
    fails on a GPU-only build and no alternate is provided via the `alt`
    keyword argument, a placeholder object will be returned which raises an
    exception only if used.

    Parameters
    ----------
    module: str
        The name of the module to import.
    alt: object
        An optional module to be used in place of the given module if it
        fails to import

    Returns
    -------
    object
        The imported module, the given alternate, or a class derived from
        UnavailableMeta.
    """
    if CPU_ENABLED:
        return importlib.import_module(module)
    else:
        return safe_import(
            module,
            msg=f"{module} is not installed in GPU-only installations",
            alt=alt,
        )


def cpu_only_import_from(module, symbol, *, alt=None):
    """A function used to import symbols required only in CPU installs

    This function will attempt to import a symbol from a module with the given
    names, but it will only throw an ImportError if the attempt fails AND this
    is not a GPU-only build. This allows CPU-only dependencies to be cleanly
    imported in GPU-only builds but guarantees that the correct exception will
    be raised if a required dependency is unavailable. If the import fails on a
    GPU-only build and no alternate is provided via the `alt` keyword
    argument, a placeholder object will be returned which raises an exception
    only if used.

    Parameters
    ----------
    module: str
        The name of the module to import.
    symbol: str
        The name of the symbol to import.
    alt: object
        An optional object to be used in place of the given symbol if it fails
        to import in a non-CPU-enabled install

    Returns
    -------
    object
        The imported symbol, the given alternate, or a class derived from
        UnavailableMeta.
    """
    if CPU_ENABLED:
        imported_module = importlib.import_module(module)
        return getattr(imported_module, symbol)
    else:
        return safe_import_from(
            module,
            symbol,
            msg=f"{module}.{symbol} is not available in GPU-only"
            " installations",
            alt=alt,
        )
