import torch
from typing import cast, Iterable, List, Union
from torch import Tensor
from .lazy_init import _lazy_init, _lazy_call

import contextlib
from typing import Generator
import warnings

__all__ = ['get_rng_state', 'get_rng_state_all',
           'set_rng_state', 'set_rng_state_all',
           'manual_seed', 'manual_seed_all',
           'seed', 'seed_all', 'initial_seed', 'fork_rng']


def get_rng_state(device: Union[int, str, torch.device] = 'xpu') -> Tensor:
    r"""Returns the random number generator state of the specified GPU as a ByteTensor.

    Args:
        device (torch.device or int, optional): The device to return the RNG state of.
            Default: ``'xpu'`` (i.e., ``torch.device('xpu')``, the current XPU device).

    .. warning::
        This function eagerly initializes XPU.
    """

    _lazy_init()
    if isinstance(device, str):
        device = torch.device(device)
    elif isinstance(device, int):
        device = torch.device('xpu', device)
    idx = device.index
    if idx is None:
        idx = torch.xpu.current_device()
    default_generator = torch.xpu.default_generators[idx]
    return default_generator.get_state()


def get_rng_state_all() -> List[Tensor]:
    r"""Returns a list of ByteTensor representing the random number states of all devices."""

    results = []
    for i in range(torch.xpu.device_count()):
        results.append(get_rng_state(i))
    return results


def set_rng_state(new_state: Tensor, device: Union[int, str, torch.device] = 'xpu') -> None:
    r"""Sets the random number generator state of the specified GPU.

    Args:
        new_state (torch.ByteTensor): The desired state
        device (torch.device or int, optional): The device to set the RNG state.
            Default: ``'xpu'`` (i.e., ``torch.device('xpu')``, the current XPU device).
    """
    new_state_copy = new_state.clone(memory_format=torch.contiguous_format)
    if isinstance(device, str):
        device = torch.device(device)
    elif isinstance(device, int):
        device = torch.device('xpu', device)

    def cb():
        idx = cast(torch.device, device).index
        if idx is None:
            idx = torch.xpu.current_device()
        default_generator = torch.xpu.default_generators[idx]
        default_generator.set_state(new_state_copy)

    _lazy_call(cb)


def set_rng_state_all(new_states: Iterable[Tensor]) -> None:
    r"""Sets the random number generator state of all devices.

    Args:
        new_states (Iterable of torch.ByteTensor): The desired state for each device"""
    for i, state in enumerate(new_states):
        set_rng_state(state, i)


def manual_seed(seed: int) -> None:
    r"""Sets the seed for generating random numbers for the current GPU.
    It's safe to call this function if XPU is not available; in that
    case, it is silently ignored.

    Args:
        seed (int): The desired seed.

    .. warning::
        If you are working with a multi-GPU model, this function is insufficient
        to get determinism.  To seed all GPUs, use :func:`manual_seed_all`.
    """
    seed = int(seed)

    def cb():
        idx = torch.xpu.current_device()
        default_generator = torch.xpu.default_generators[idx]
        default_generator.manual_seed(seed)

    _lazy_call(cb)


def manual_seed_all(seed: int) -> None:
    r"""Sets the seed for generating random numbers on all GPUs.
    It's safe to call this function if XPU is not available; in that
    case, it is silently ignored.

    Args:
        seed (int): The desired seed.
    """
    seed = int(seed)

    def cb():
        for i in range(torch.xpu.device_count()):
            default_generator = torch.xpu.default_generators[i]
            default_generator.manual_seed(seed)

    _lazy_call(cb, seed_all=True)


def seed() -> None:
    r"""Sets the seed for generating random numbers to a random number for the current GPU.
    It's safe to call this function if XPU is not available; in that
    case, it is silently ignored.

    .. warning::
        If you are working with a multi-GPU model, this function will only initialize
        the seed on one GPU.  To initialize all GPUs, use :func:`seed_all`.
    """
    def cb():
        idx = torch.xpu.current_device()
        default_generator = torch.xpu.default_generators[idx]
        default_generator.seed()

    _lazy_call(cb)


def seed_all() -> None:
    r"""Sets the seed for generating random numbers to a random number on all GPUs.
    It's safe to call this function if XPU is not available; in that
    case, it is silently ignored.
    """
    def cb():
        random_seed = 0
        seeded = False
        for i in range(torch.xpu.device_count()):
            default_generator = torch.xpu.default_generators[i]
            if not seeded:
                default_generator.seed()
                random_seed = default_generator.initial_seed()
                seeded = True
            else:
                default_generator.manual_seed(random_seed)

    _lazy_call(cb)


def initial_seed() -> int:
    r"""Returns the current random seed of the current GPU.

    .. warning::
        This function eagerly initializes XPU.
    """

    # lazy initialization occurs in current_device
    idx = torch.xpu.current_device()
    default_generator = torch.xpu.default_generators[idx]
    return default_generator.initial_seed()


_fork_rng_warned_already = False


@contextlib.contextmanager
def fork_rng(devices=None, enabled=True, _caller="fork_rng", _devices_kw="devices") -> Generator:
    """
    Forks the RNG, so that when you return, the RNG is reset
    to the state that it was previously in.

    Args:
        devices (iterable of XPU IDs): XPU devices for which to fork
            the RNG.  CPU RNG state is always forked.  By default, :meth:`fork_rng` operates
            on all devices, but will emit a warning if your machine has a lot
            of devices, since this function will run very slowly in that case.
            If you explicitly specify devices, this warning will be suppressed
        enabled (bool): if ``False``, the RNG is not forked.  This is a convenience
            argument for easily disabling the context manager without having
            to delete it and unindent your Python code under it.
    """

    global _fork_rng_warned_already

    # Internal arguments:
    #   _caller: the function which called fork_rng, which the user used
    #   _devices_kw: the devices keyword of _caller

    if not enabled:
        yield
        return

    if devices is None:
        num_devices = torch.xpu.device_count()
        if num_devices > 1 and not _fork_rng_warned_already:
            warnings.warn(
                ("XPU reports that you have {num_devices} available devices, and you "
                 "have used {caller} without explicitly specifying which devices are being used. "
                 "For safety, we initialize *every* XPU device by default, which "
                 "can be quite slow if you have a lot of GPUs.  If you know that you are only "
                 "making use of a few XPU devices, set the environment variable XPU_VISIBLE_DEVICES "
                 "or the '{devices_kw}' keyword argument of {caller} with the set of devices "
                 "you are actually using.  For example, if you are using CPU only, "
                 "set XPU_VISIBLE_DEVICES= or devices=[]; if you are using "
                 "GPU 0 only, set XPU_VISIBLE_DEVICES=0 or devices=[0].  To initialize "
                 "all devices and suppress this warning, set the '{devices_kw}' keyword argument "
                 "to `range(torch.xpu.device_count())`."
                 ).format(num_devices=num_devices, caller=_caller, devices_kw=_devices_kw))
            _fork_rng_warned_already = True
        devices = list(range(num_devices))
    else:
        # Protect against user passing us a generator; we need to traverse this
        # multiple times but a generator will be exhausted upon first traversal
        devices = list(devices)

    cpu_rng_state = torch.get_rng_state()
    gpu_rng_states = []
    for device in devices:
        gpu_rng_states.append(torch.xpu.get_rng_state(device))

    try:
        yield
    finally:
        torch.set_rng_state(cpu_rng_state)
        for device, gpu_rng_state in zip(devices, gpu_rng_states):
            torch.xpu.set_rng_state(gpu_rng_state, device)
