# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
"""Attention layer with AiterFlashAttention."""

from dataclasses import dataclass

import torch

from vllm.attention.backends.abstract import (
    AttentionBackend,
    AttentionImpl,
    AttentionMetadata,
    AttentionType,
    MultipleOf,
)
from vllm.config import VllmConfig
from vllm.logger import init_logger
from vllm.platforms import current_platform
from vllm.v1.attention.backends.utils import (
    AttentionCGSupport,
    AttentionMetadataBuilder,
    CommonAttentionMetadata,
)
from vllm.v1.kv_cache_interface import AttentionSpec

_PARTITION_SIZE_ROCM = 256

if current_platform.is_rocm():
    import aiter

    from vllm.triton_utils import tl, triton
    from vllm.utils import direct_register_custom_op

    @triton.jit
    def _vllm_layout_trans_kernel(
        k_buffer_ptr,
        v_buffer_ptr,
        k_values_ptr,
        v_values_ptr,
        b_query_lens_loc,
        b_seq_lens_loc,
        block_table,
        block_table_stride_0,
        k_scale,
        v_scale,
        output_dtype: tl.constexpr,
        E_DIM: tl.constexpr,
        BLOCK_SIZE: tl.constexpr,
    ):
        batch_idx = tl.program_id(0)
        block_idx = tl.program_id(1)

        batch_query_indexes = tl.load(b_query_lens_loc + batch_idx + tl.arange(0, 2))
        batch_query_start, batch_query_end = tl.split(batch_query_indexes)
        query_len = batch_query_end - batch_query_start

        if query_len <= 1:
            return

        batch_token_indexes = tl.load(b_seq_lens_loc + batch_idx + tl.arange(0, 2))
        batch_token_start, batch_token_end = tl.split(batch_token_indexes)
        seq_len = batch_token_end - batch_token_start

        if block_idx * BLOCK_SIZE < seq_len:
            block_mask = (
                block_idx * BLOCK_SIZE + tl.arange(0, BLOCK_SIZE)[:, None]
            ) < seq_len

            kv_idx = tl.load(
                block_table + batch_idx * block_table_stride_0 + block_idx
            ).to(tl.int64)

            kv_buffer_off = (
                kv_idx * BLOCK_SIZE * E_DIM
                + tl.arange(0, BLOCK_SIZE)[:, None] * E_DIM
                + tl.arange(0, E_DIM)[None, :]
            )
            k_vals = tl.load(k_buffer_ptr + kv_buffer_off, mask=block_mask, other=0.0)
            if k_vals.dtype.is_fp8():
                k_vals = (k_vals.to(tl.float32) * tl.load(k_scale)).to(output_dtype)
            else:
                k_vals = k_vals.to(output_dtype)

            v_vals = tl.load(v_buffer_ptr + kv_buffer_off, mask=block_mask, other=0.0)
            if v_vals.dtype.is_fp8():
                v_vals = (v_vals.to(tl.float32) * tl.load(v_scale)).to(output_dtype)
            else:
                v_vals = v_vals.to(output_dtype)
            kv_values_off = (
                batch_token_start * E_DIM
                + block_idx * BLOCK_SIZE * E_DIM
                + tl.arange(0, BLOCK_SIZE)[:, None] * E_DIM
                + tl.arange(0, E_DIM)[None, :]
            )
            tl.store(k_values_ptr + kv_values_off, k_vals, mask=block_mask)
            tl.store(v_values_ptr + kv_values_off, v_vals, mask=block_mask)

    def vllm_layout_trans(
        b_query_lens_loc,
        b_seq_lens_loc,
        block_table,
        k_cache,
        v_cache,
        max_seq_len,
        k_scale,
        v_scale,
        output_dtype,
        total_tokens,
    ):
        H_KV = v_cache.shape[2]
        D = v_cache.shape[3]
        BLOCK_SIZE = v_cache.shape[1]

        k_values = torch.empty(
            (total_tokens, H_KV, D),
            dtype=output_dtype,
            device=k_cache.device,
        )
        v_values = torch.empty(
            (total_tokens, H_KV, D),
            dtype=output_dtype,
            device=v_cache.device,
        )

        grid = (block_table.shape[0], (max_seq_len + BLOCK_SIZE - 1) // BLOCK_SIZE)

        if output_dtype == torch.float16:
            output_dtype = tl.float16
        elif output_dtype == torch.bfloat16:
            output_dtype = tl.bfloat16
        else:
            raise ValueError(f"Unsupported output dtype: {output_dtype}")

        _vllm_layout_trans_kernel[grid](
            k_cache,
            v_cache,
            k_values,
            v_values,
            b_query_lens_loc,
            b_seq_lens_loc,
            block_table,
            block_table.stride(0),
            k_scale,
            v_scale,
            output_dtype=output_dtype,
            E_DIM=H_KV * D,
            BLOCK_SIZE=BLOCK_SIZE,
        )

        return k_values, v_values

    def flash_attn_varlen_func_impl(
        q: torch.Tensor,
        k_cache: torch.Tensor,
        v_cache: torch.Tensor,
        out: torch.Tensor,
        cu_seqlens_q: torch.Tensor,
        cu_seqlens_k: torch.Tensor,
        max_seqlen_q: int,
        max_seqlen_k: int,
        softmax_scale: float,
        window_size: list[int] | None,  # -1 means infinite context window
        alibi_slopes: list[float] | None,
        block_table: torch.Tensor,
        k_scale: torch.Tensor,
        v_scale: torch.Tensor,
        total_tokens: int = 0,
    ) -> torch.Tensor:
        if total_tokens == 0:
            total_tokens = int(cu_seqlens_k[-1].item())
        k, v = vllm_layout_trans(
            cu_seqlens_q,
            cu_seqlens_k,
            block_table,
            k_cache,
            v_cache,
            max_seqlen_k,
            k_scale,
            v_scale,
            q.dtype,
            total_tokens,
        )

        output = aiter.flash_attn_varlen_func(
            q=q,
            k=k,
            v=v,
            cu_seqlens_q=cu_seqlens_q,
            max_seqlen_q=max_seqlen_q,
            min_seqlen_q=1,
            cu_seqlens_k=cu_seqlens_k,
            max_seqlen_k=max_seqlen_k,
            softmax_scale=softmax_scale,
            causal=True,
            alibi_slopes=alibi_slopes,
            window_size=window_size,
            out=out,
        )
        return output

    def flash_attn_varlen_func_fake(
        q: torch.Tensor,
        k_cache: torch.Tensor,
        v_cache: torch.Tensor,
        out: torch.Tensor,
        cu_seqlens_q: torch.Tensor,
        cu_seqlens_k: torch.Tensor,
        max_seqlen_q: int,
        max_seqlen_k: int,
        softmax_scale: float,
        window_size: list[int] | None,  # -1 means infinite context window
        alibi_slopes: list[float] | None,
        block_table: torch.Tensor,
        k_scale: torch.Tensor,
        v_scale: torch.Tensor,
        total_tokens: int = 0,
    ) -> torch.Tensor:
        return torch.empty(
            q.shape[0], q.shape[1], v_cache.shape[-2], dtype=q.dtype, device=q.device
        )

    direct_register_custom_op(
        "flash_attn_varlen_func",
        flash_attn_varlen_func_impl,
        ["out"],
        flash_attn_varlen_func_fake,
        dispatch_key=current_platform.dispatch_key,
    )

logger = init_logger(__name__)


@dataclass
class AiterFlashAttentionMetadata:
    # NOTE(sang): Definition of context_len, query_len, and seq_len.
    # |---------- N-1 iteration --------|
    # |---------------- N iteration ---------------------|
    # |- tokenA -|......................|-- newTokens ---|
    # |---------- context_len ----------|
    # |-------------------- seq_len ---------------------|
    #                                   |-- query_len ---|

    num_actual_tokens: int  # Number of tokens excluding padding.
    num_actual_kv_tokens: int
    max_query_len: int
    query_start_loc: torch.Tensor
    max_seq_len: int
    seq_lens: torch.Tensor
    slot_mapping: torch.Tensor
    block_table: torch.Tensor
    cu_seq_lens: torch.Tensor | None

    # For cascade attention.
    use_cascade: bool
    common_prefix_len: int
    total_tokens: int


class AiterFlashAttentionMetadataBuilder(
    AttentionMetadataBuilder[AiterFlashAttentionMetadata]
):
    cudagraph_support = AttentionCGSupport.UNIFORM_SINGLE_TOKEN_DECODE

    def __init__(
        self,
        kv_cache_spec: AttentionSpec,
        layer_names: list[str],
        vllm_config: VllmConfig,
        device: torch.device,
    ):
        super().__init__(kv_cache_spec, layer_names, vllm_config, device)

        self.model_config = vllm_config.model_config
        self.parallel_config = vllm_config.parallel_config
        self.cache_config = vllm_config.cache_config

        self.num_heads_q = self.model_config.get_num_attention_heads(
            self.parallel_config
        )
        self.num_heads_kv = self.model_config.get_num_kv_heads(self.parallel_config)
        self.headdim = self.model_config.get_head_size()
        self.block_size = kv_cache_spec.block_size
        # Sliding window size to be used with the AOT scheduler will be
        # populated on first build() call.
        self.aot_sliding_window: tuple[int, int] | None = None
        self.total_tokens: int = 0

    def build_for_cudagraph_capture(
        self, common_attn_metadata: CommonAttentionMetadata
    ):
        self.total_tokens = (
            self.model_config.max_model_len
            * self.vllm_config.scheduler_config.max_num_partial_prefills
        )
        res = self.build(common_prefix_len=0, common_attn_metadata=common_attn_metadata)
        self.total_tokens = 0
        return res

    def build(
        self,
        common_prefix_len: int,
        common_attn_metadata: CommonAttentionMetadata,
        fast_build: bool = False,
    ) -> "AiterFlashAttentionMetadata":
        num_actual_tokens = common_attn_metadata.num_actual_tokens
        max_query_len = common_attn_metadata.max_query_len
        max_seq_len = common_attn_metadata.max_seq_len
        query_start_loc = common_attn_metadata.query_start_loc
        seq_lens = common_attn_metadata.seq_lens
        block_table_tensor = common_attn_metadata.block_table_tensor
        slot_mapping = common_attn_metadata.slot_mapping
        if max_query_len > 1:
            # We pre-compute cumulative seq len needed for prefill attention
            # here to avoid recomputing it for every layer
            cu_seq_lens = torch.zeros(
                seq_lens.shape[0] + 1, dtype=torch.int32, device=seq_lens.device
            )
            torch.cumsum(seq_lens, dim=0, dtype=cu_seq_lens.dtype, out=cu_seq_lens[1:])
            num_actual_kv_tokens = int(cu_seq_lens[-1].item())
        else:
            cu_seq_lens = None
            num_actual_kv_tokens = 0

        def schedule(
            batch_size, cu_query_lens, max_query_len, seqlens, max_seq_len, causal
        ):
            return None

        use_cascade = common_prefix_len > 0

        attn_metadata = AiterFlashAttentionMetadata(
            num_actual_tokens=num_actual_tokens,
            num_actual_kv_tokens=num_actual_kv_tokens,
            max_query_len=max_query_len,
            query_start_loc=query_start_loc,
            max_seq_len=max_seq_len,
            seq_lens=seq_lens,
            block_table=block_table_tensor,
            slot_mapping=slot_mapping,
            cu_seq_lens=cu_seq_lens,
            use_cascade=use_cascade,
            common_prefix_len=common_prefix_len,
            total_tokens=self.total_tokens,
        )
        return attn_metadata

    def use_cascade_attention(self, *args, **kwargs) -> bool:
        return False


class AiterFlashAttentionBackend(AttentionBackend):
    accept_output_buffer: bool = True

    @classmethod
    def get_supported_dtypes(cls) -> list[torch.dtype]:
        return [torch.float16, torch.bfloat16]

    @classmethod
    def get_supported_head_sizes(cls) -> list[int]:
        return [64, 128, 256]

    @staticmethod
    def get_supported_kernel_block_size() -> list[int | MultipleOf]:
        return [MultipleOf(16)]

    @classmethod
    def validate_head_size(cls, head_size: int) -> None:
        supported_head_sizes = cls.get_supported_head_sizes()
        if head_size not in supported_head_sizes:
            attn_type = cls.__name__.removesuffix("Backend")
            raise ValueError(
                f"Head size {head_size} is not supported by {attn_type}. "
                f"Supported head sizes are: {supported_head_sizes}. "
                "Set VLLM_ATTENTION_BACKEND=FLEX_ATTENTION to use "
                "FlexAttention backend which supports all head sizes."
            )

    @staticmethod
    def get_name() -> str:
        return "FLASH_ATTN"

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

    @staticmethod
    def get_metadata_cls() -> type["AttentionMetadata"]:
        return AiterFlashAttentionMetadata

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

    @staticmethod
    def get_kv_cache_shape(
        num_blocks: int,
        block_size: int,
        num_kv_heads: int,
        head_size: int,
        cache_dtype_str: str = "auto",
    ) -> tuple[int, ...]:
        if block_size % 16 != 0:
            raise ValueError("Block size must be a multiple of 16.")
        return (2, num_blocks, block_size, num_kv_heads, head_size)


class AiterFlashAttentionImpl(AttentionImpl):
    def __init__(
        self,
        num_heads: int,
        head_size: int,
        scale: float,
        num_kv_heads: int,
        alibi_slopes: list[float] | None,
        sliding_window: int | None,
        kv_cache_dtype: str,
        logits_soft_cap: float | None = None,
        attn_type: AttentionType = AttentionType.DECODER,
        kv_sharing_target_layer_name: int | None = None,
    ) -> None:
        self.num_heads = num_heads
        self.head_size = head_size
        self.scale = float(scale)
        self.num_kv_heads = num_kv_heads
        if alibi_slopes is not None:
            alibi_slopes = torch.tensor(alibi_slopes, dtype=torch.float32)
        self.alibi_slopes = alibi_slopes
        if sliding_window is None:
            self.sliding_window = [-1, -1]
        else:
            self.sliding_window = [sliding_window - 1, 0]
        self.kv_cache_dtype = kv_cache_dtype
        if logits_soft_cap is None:
            # In flash-attn, setting logits_soft_cap as 0 means no soft cap.
            logits_soft_cap = 0.0
        self.logits_soft_cap = logits_soft_cap
        self.kv_sharing_target_layer_name = kv_sharing_target_layer_name

        assert self.num_heads % self.num_kv_heads == 0
        self.num_queries_per_kv = self.num_heads // self.num_kv_heads

        AiterFlashAttentionBackend.validate_head_size(head_size)

        if attn_type != AttentionType.DECODER:
            raise NotImplementedError(
                "Encoder self-attention and "
                "encoder/decoder cross-attention "
                "are not implemented for "
                "FlashAttentionImpl"
            )

    def forward(
        self,
        layer: torch.nn.Module,
        query: torch.Tensor,
        key: torch.Tensor,
        value: torch.Tensor,
        kv_cache: torch.Tensor,
        attn_metadata: AiterFlashAttentionMetadata,
        output: torch.Tensor | None = None,
        output_scale: torch.Tensor | None = None,
        output_block_scale: torch.Tensor | None = None,
    ) -> torch.Tensor:
        """Forward pass with AiterFlashAttention.

        Args:
            query: shape = [num_tokens, num_heads, head_size]
            key: shape = [num_tokens, num_kv_heads, head_size]
            value: shape = [num_tokens, num_kv_heads, head_size]
            kv_cache: shape =
                [2, num_blocks, block_size, num_kv_heads, head_size]
            attn_metadata: Metadata for attention.
        Returns:
            shape = [num_tokens, num_heads * head_size]
        NOTE: FP8 quantization, flash-attn expect the size of
              {q,k,v}_descale to be (num_sequences, num_kv_heads).
              We use torch's .expand() to avoid duplicating values
        """
        assert output is not None, "Output tensor must be provided."

        if output_scale is not None or output_block_scale is not None:
            raise NotImplementedError(
                "fused output quantization is not yet supported for FlashAttentionImpl"
            )

        if attn_metadata is None:
            # Profiling run.
            return output.fill_(0)

        # IMPORTANT!
        # NOTE(woosuk): With piece-wise CUDA graphs, this method is executed in
        # eager-mode PyTorch. Thus, we need to be careful about any CPU overhead
        # in this method. For example, `view` and `slice` (or `[:n]`) operations
        # are surprisingly slow even in the case they do not invoke any GPU ops.
        # Minimize the PyTorch ops in this method as much as possible.
        # Whenever making a change in this method, please benchmark the
        # performance to make sure it does not introduce any overhead.

        num_actual_tokens = attn_metadata.num_actual_tokens
        key_cache, value_cache = kv_cache.unbind(0)
        if self.kv_sharing_target_layer_name is None:
            # Reshape the input keys and values and store them in the cache.
            # Skip this if sharing KV cache with an earlier attention layer.
            # NOTE(woosuk): Here, key and value are padded while slot_mapping is
            # not padded. However, we don't need to do key[:num_actual_tokens]
            # and value[:num_actual_tokens] because the reshape_and_cache_flash
            # op uses the slot_mapping's shape to determine the number of
            # actual tokens.
            torch.ops._C_cache_ops.reshape_and_cache_flash(
                key,
                value,
                key_cache,
                value_cache,
                attn_metadata.slot_mapping,
                self.kv_cache_dtype,
                layer._k_scale,
                layer._v_scale,
            )

        if self.kv_cache_dtype.startswith("fp8"):
            key_cache = key_cache.view(current_platform.fp8_dtype())
            value_cache = value_cache.view(current_platform.fp8_dtype())

        if not attn_metadata.use_cascade:
            cu_seqlens_q = attn_metadata.query_start_loc
            seqused_k = attn_metadata.seq_lens
            max_seqlen_q = attn_metadata.max_query_len
            max_seqlen_k = attn_metadata.max_seq_len
            block_table = attn_metadata.block_table

            if max_seqlen_q > 1:
                torch.ops.vllm.flash_attn_varlen_func(
                    query[:num_actual_tokens],
                    key_cache,
                    value_cache,
                    out=output[:num_actual_tokens],
                    cu_seqlens_q=cu_seqlens_q,
                    max_seqlen_q=max_seqlen_q,
                    max_seqlen_k=max_seqlen_k,
                    softmax_scale=self.scale,
                    alibi_slopes=self.alibi_slopes,
                    window_size=self.sliding_window,
                    block_table=block_table,
                    cu_seqlens_k=attn_metadata.cu_seq_lens,
                    k_scale=layer._k_scale,
                    v_scale=layer._v_scale,
                    total_tokens=attn_metadata.num_actual_kv_tokens,
                )

            _, num_heads, head_size = query.shape
            nbytes_per_qo_elem = torch.finfo(query.dtype).bits // 8
            num_seqs = seqused_k.shape[0]
            max_num_partitions = (
                max_seqlen_k + _PARTITION_SIZE_ROCM - 1
            ) // _PARTITION_SIZE_ROCM

            workspace_buffer = torch.empty(
                (num_seqs * num_heads * max_num_partitions * head_size)
                * nbytes_per_qo_elem
                + 2 * (num_seqs * num_heads * max_num_partitions) * 4,
                dtype=torch.uint8,
                device=output.device,
            )

            torch.ops.aiter.paged_attention_v1(
                output[:num_actual_tokens],
                workspace_buffer,
                query[:num_actual_tokens],
                key_cache,
                value_cache,
                self.scale,
                block_table,
                cu_seqlens_q,
                seqused_k,
                max_seqlen_k,
                self.alibi_slopes,
                self.kv_cache_dtype,
                "NHD",
                self.logits_soft_cap,
                layer._k_scale,
                layer._v_scale,
                None,
                _PARTITION_SIZE_ROCM,
            )
            return output
        else:
            raise NotImplementedError(
                "Cascade attention is not implemented for ROCM AITER"
            )
