from __future__ import annotations

import logging
from enum import Enum
from typing import TYPE_CHECKING

from sglang.srt.utils.common import is_sm120_supported

if TYPE_CHECKING:
    from sglang.srt.server_args import ServerArgs

logger = logging.getLogger(__name__)


class Fp4GemmRunnerBackend(Enum):
    """Enum for FP4 GEMM runner backend selection."""

    AUTO = "auto"
    FLASHINFER_CUDNN = "flashinfer_cudnn"
    FLASHINFER_CUTLASS = "flashinfer_cutlass"
    FLASHINFER_TRTLLM = "flashinfer_trtllm"

    def is_auto(self) -> bool:
        return self == Fp4GemmRunnerBackend.AUTO

    def is_flashinfer_cudnn(self) -> bool:
        return self == Fp4GemmRunnerBackend.FLASHINFER_CUDNN

    def is_flashinfer_cutlass(self) -> bool:
        return self == Fp4GemmRunnerBackend.FLASHINFER_CUTLASS

    def is_flashinfer_trtllm(self) -> bool:
        return self == Fp4GemmRunnerBackend.FLASHINFER_TRTLLM

    def get_flashinfer_backend(self) -> str:
        """Get the backend string to pass to FlashInfer's mm_fp4 API.

        This remaps SGLang's user-facing backend names to FlashInfer's API names.
        Examples:
            'flashinfer_trtllm' -> 'trtllm'
            'flashinfer_cutlass' -> 'cutlass'
            'flashinfer_cudnn' -> 'cudnn'
        """
        if self.value.startswith("flashinfer_"):
            return self.value.removeprefix("flashinfer_")
        else:
            return self.value


FP4_GEMM_RUNNER_BACKEND: Fp4GemmRunnerBackend | None = None


def initialize_fp4_gemm_config(server_args: ServerArgs) -> None:
    """Initialize FP4 GEMM configuration from server args."""
    global FP4_GEMM_RUNNER_BACKEND

    backend = server_args.fp4_gemm_runner_backend
    if backend == "auto":
        if is_sm120_supported():
            # flashinfer_cutlass produces NaN in dense MLP layers with
            # heterogeneous batches on SM120 (Blackwell).  cudnn is stable.
            # See: https://github.com/sgl-project/sglang/issues/20043
            backend = "flashinfer_cudnn"
            logger.info(
                "SM120 (Blackwell) detected: auto-selecting "
                "fp4-gemm-backend=flashinfer_cudnn"
            )
        else:
            backend = "flashinfer_cutlass"

    FP4_GEMM_RUNNER_BACKEND = Fp4GemmRunnerBackend(backend)


def get_fp4_gemm_runner_backend() -> Fp4GemmRunnerBackend:
    """Get the current FP4 GEMM runner backend."""
    global FP4_GEMM_RUNNER_BACKEND
    if FP4_GEMM_RUNNER_BACKEND is None:
        FP4_GEMM_RUNNER_BACKEND = Fp4GemmRunnerBackend.AUTO
    return FP4_GEMM_RUNNER_BACKEND
