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# SPDX-License-Identifier: Apache-2.0
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# http://www.apache.org/licenses/LICENSE-2.0
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"""
Imaginaire4 Attention Subpackage:
Unified implementation for all Attention implementations.

Flash Attention v3 (flash3) Backend
"""

import torch

from cosmos_predict2._src.imaginaire.attention.utils import safe_log as log

FLASH_ATTENTION_V3_MIN_VERSION = [1, 0, 0]


def flash3_supported() -> bool:
    """
    Returns whether Flash Attention is supported in this environment.
    Requirements are:
        * Presence of CUDA Runtime (via PyTorch)
        * Presence of Flash Attention, meeting minimum version requirements

    This check guards imports / dependencies on the Flash Attention package.
    """
    if not torch.cuda.is_available():
        log.debug("Flash Attention v3 is not supported because PyTorch did not detect CUDA runtime.")
        return False

    try:
        # pyrefly: ignore  # missing-import
        import flash_attn_3_nv

    except ImportError:
        log.debug("Flash Attention v3 is not supported because the Python package ('flash_attn_3_nv'_) was not found.")
        return False
    except Exception as e:
        log.debug(f"Flash Attention v3 is not supported because importing the Python package failed: {e}")
        return False

    flash3_version_str = flash_attn_3_nv.__version__

    flash3_version_split = flash3_version_str.split(".")
    if len(flash3_version_split) != 3:
        log.debug(f"Unable to parse Flash Attention v3 ('flash_attn_3_nv') version {flash3_version_str}.")
        return False

    try:
        flash3_version = [int(x) for x in flash3_version_split]

    except ValueError:
        log.debug(
            f"Unable to parse Flash Attention v3 ('flash_attn_3_nv') version as an int list: {flash3_version_str}."
        )
        return False

    if flash3_version < FLASH_ATTENTION_V3_MIN_VERSION:
        log.debug(
            "Flash Attention v3 ('flash_attn_3_nv') build is not supported; minimum required version is"
            f"{FLASH_ATTENTION_V3_MIN_VERSION}, got "
            f"{flash3_version}."
        )
        return False

    return True


FLASH3_SUPPORTED = flash3_supported()


if FLASH3_SUPPORTED:
    from cosmos_predict2._src.imaginaire.attention.flash3.functions import flash3_attention

else:
    from cosmos_predict2._src.imaginaire.attention.flash3.stubs import flash3_attention

__all__ = ["flash3_attention", "FLASH3_SUPPORTED"]