import pytest
import torch

from liger_kernel.utils import is_npu_available
from test.utils import set_seed


@pytest.fixture(autouse=True)
def set_random_seed():
    set_seed(42)


@pytest.fixture(autouse=True)
def clear_gpu_cache():
    yield
    if torch.cuda.is_available():
        torch.cuda.empty_cache()
    elif is_npu_available():
        torch.npu.empty_cache()
    elif torch.xpu.is_available():
        torch.xpu.empty_cache()


@pytest.fixture(autouse=True)
def reset_liger_backend_selection():
    """Isolate global backend/impl selection between tests.

    Several op tests call ``set_impl``/``set_backend`` (or set the
    ``LIGER_KERNEL_IMPL*`` env) to exercise a specific backend. Without a reset,
    that global choice leaks into every later test in the session, which routed
    unrelated ops (cross_entropy, tvd, dyt, ...) through a backend they were
    never meant to use and produced order-dependent failures. Restore the
    default (auto) selection and drop the availability memo after each test.
    """
    yield
    try:
        from liger_kernel.backends.dispatch import clear_available_cache
        from liger_kernel.backends.dispatch import set_impl

        set_impl(None)
        clear_available_cache()
    except Exception:
        pass