from dataclasses import dataclass
from typing import Any

import torch

from sglang.multimodal_gen.runtime.layers.attention.backends.attention_backend import (
    AttentionBackend,
    AttentionImpl,
    AttentionMetadata,
    AttentionMetadataBuilder,
)
from sglang.multimodal_gen.runtime.platforms import AttentionBackendEnum
from sglang.multimodal_gen.runtime.utils.logging_utils import init_logger

logger = init_logger(__name__)


@dataclass
class AscendFAMetadata:
    pass


class AscendFAMetadataBuilder(AttentionMetadataBuilder):
    def __init__(self) -> None:
        pass

    def prepare(self) -> None:
        pass

    def build(
        self,
        **kwargs: dict[str, Any],
    ) -> AttentionMetadata:
        return AscendFAMetadata()


class AscendFABackend(AttentionBackend):

    @staticmethod
    def get_enum() -> AttentionBackendEnum:
        return AttentionBackendEnum.FA

    @staticmethod
    def get_impl_cls() -> type["AscendFAImpl"]:
        return AscendFAImpl

    @staticmethod
    def get_metadata_cls() -> type["AttentionMetadata"]:
        raise NotImplementedError

    @staticmethod
    def get_builder_cls() -> type["AttentionMetadataBuilder"]:
        return AscendFAMetadataBuilder


class AscendFAImpl(AttentionImpl):

    def __init__(
        self,
        num_heads: int,
        head_size: int,
        causal: bool,
        softmax_scale: float,
        num_kv_heads: int | None = None,
        prefix: str = "",
        **extra_impl_args,
    ) -> None:
        self.causal = causal
        self.softmax_scale = softmax_scale
        self.num_heads = num_heads
        self.num_kv_heads = num_kv_heads or num_heads

    def forward(
        self,
        query: torch.Tensor,
        key: torch.Tensor,
        value: torch.Tensor,
        attn_metadata: AttentionMetadata,
        return_softmax_lse: bool = False,
    ) -> torch.Tensor:
        mask = None
        if self.causal:
            seq_len = query.shape[1]
            mask = torch.triu(
                torch.ones(seq_len, seq_len, device=query.device), diagonal=1
            ).bool()
        # transpose to bs, heads, seq_len, head_dim
        query = query.transpose(1, 2)
        key = key.transpose(1, 2)
        value = value.transpose(1, 2)
        output, lse = torch.ops.npu.npu_fused_infer_attention_score(
            query,
            key,
            value,
            num_heads=self.num_heads,
            num_key_value_heads=self.num_kv_heads,
            scale=self.softmax_scale,
            input_layout="BNSD",
            softmax_lse_flag=return_softmax_lse,
            atten_mask=mask,
        )
        output = output.transpose(1, 2)
        if return_softmax_lse:
            return output, lse
        return output
