import torch

cmo_stream = None


def get_cmo_stream():
    """
    Cache Management Operation(CMO).
    Launch a new stream to prefetch the weight of matmul when running other
    AIV or communication kernels, aiming to overlap the memory access time.
    """
    global cmo_stream
    return cmo_stream


def set_cmo_stream(stream):
    global cmo_stream
    cmo_stream = stream


def prepare_weight_cache(handle, cache, PREFETCH_MAX_SIZE=1000000000):
    """
    PREFETCH_MAX_SIZE: maximum size (bytes) for each prefetch operation.
    This affects the time spent in prefetch:
        time ≈ PREFETCH_MAX_SIZE / system_bandwidth
    """
    import torch_npu

    stream = get_cmo_stream()
    if stream is None:
        stream = torch.npu.Stream()
        set_cmo_stream(stream)
    stream.wait_stream(torch.npu.current_stream())
    with torch.npu.stream(stream):
        if isinstance(cache, list):
            for weight in cache:
                torch_npu.npu_prefetch(
                    weight,
                    handle,
                    PREFETCH_MAX_SIZE,
                )
        else:
            torch_npu.npu_prefetch(
                cache,
                handle,
                PREFETCH_MAX_SIZE,
            )


def wait_cmo_stream():
    stream = get_cmo_stream()
    if stream is not None:
        cur_stream = torch.npu.current_stream()
        cur_stream.wait_stream(stream)