# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
# SPDX-FileCopyrightText: Songlin Yang, Yu Zhang
#
# This file contains code copied from the flash-linear-attention project.
# The original source code was licensed under the MIT license and included
# the following copyright notice:
# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
# ruff: noqa: E501
from typing import Optional

import torch

from vllm.triton_utils import tl, triton

from .index import prepare_chunk_indices
from .op import exp


@triton.heuristics({
    'IS_VARLEN': lambda args: args['cu_seqlens'] is not None,
    'USE_G': lambda args: args['g_cumsum'] is not None
})
@triton.autotune(
    configs=[
        triton.Config({'BK': BK}, num_warps=num_warps, num_stages=num_stages)
        for BK in [32, 64, 128] for num_warps in [2, 4, 8]
        for num_stages in [2, 3, 4]
    ],
    key=['H', 'K', 'BT', 'IS_VARLEN'],
)
@triton.jit(do_not_specialize=['T'])
def chunk_scaled_dot_kkt_fwd_kernel(
    k,
    beta,
    g_cumsum,
    A,
    cu_seqlens,
    chunk_indices,
    T,
    H: tl.constexpr,
    Hg: tl.constexpr,
    K: tl.constexpr,
    BT: tl.constexpr,
    BK: tl.constexpr,
    IS_VARLEN: tl.constexpr,
    USE_G: tl.constexpr,
):
    i_t, i_bh = tl.program_id(0), tl.program_id(1)
    i_b, i_h = i_bh // H, i_bh % H
    if IS_VARLEN:
        i_n, i_t = tl.load(chunk_indices + i_t * 2).to(
            tl.int32), tl.load(chunk_indices + i_t * 2 + 1).to(tl.int32)
        bos, eos = tl.load(cu_seqlens + i_n).to(
            tl.int32), tl.load(cu_seqlens + i_n + 1).to(tl.int32)
        T = eos - bos
    else:
        bos, eos = i_b * T, i_b * T + T
    o_t = i_t * BT + tl.arange(0, BT)
    m_t = o_t < T

    p_beta = tl.make_block_ptr(beta + bos * H + i_h, (T, ), (H, ),
                               (i_t * BT, ), (BT, ), (0, ))
    b_beta = tl.load(p_beta, boundary_check=(0, ))

    b_A = tl.zeros([BT, BT], dtype=tl.float32)
    for i_k in range(tl.cdiv(K, BK)):
        p_k = tl.make_block_ptr(k + (bos * Hg + i_h // (H // Hg)) * K, (T, K),
                                (Hg * K, 1), (i_t * BT, i_k * BK), (BT, BK),
                                (1, 0))
        b_k = tl.load(p_k, boundary_check=(0, 1))
        b_kb = b_k * b_beta[:, None]
        b_A += tl.dot(b_kb.to(b_k.dtype), tl.trans(b_k))

    if USE_G:
        p_g = tl.make_block_ptr(g_cumsum + bos * H + i_h, (T, ), (H, ),
                                (i_t * BT, ), (BT, ), (0, ))
        b_g = tl.load(p_g, boundary_check=(0, ))
        b_g_diff = b_g[:, None] - b_g[None, :]
        b_A = b_A * exp(b_g_diff)

    m_A = (o_t[:, None] > o_t[None, :]) & (m_t[:, None] & m_t)
    b_A = tl.where(m_A, b_A, 0)
    p_A = tl.make_block_ptr(A + (bos * H + i_h) * BT, (T, BT), (BT * H, 1),
                            (i_t * BT, 0), (BT, BT), (1, 0))
    tl.store(p_A, b_A.to(p_A.dtype.element_ty), boundary_check=(0, 1))


def chunk_scaled_dot_kkt_fwd(
        k: torch.Tensor,
        beta: torch.Tensor,
        g_cumsum: Optional[torch.Tensor] = None,
        cu_seqlens: Optional[torch.LongTensor] = None,
        chunk_size: int = 64,
        output_dtype: torch.dtype = torch.float32) -> torch.Tensor:
    r"""
    Compute beta * K * K^T.

    Args:
        k (torch.Tensor):
            The key tensor of shape `[B, T, H, K]`.
        beta (torch.Tensor):
            The beta tensor of shape `[B, T, H]`.
        g_cumsum (torch.Tensor):
            The cumulative sum of the gate tensor of shape `[B, T, H]`.
            Default: None
        cu_seqlens (torch.LongTensor):
            The cumulative sequence lengths of the input tensor.
            Default: None
        chunk_size (int):
            The chunk size. Default: 64.
        output_dtype (torch.dtype):
            The dtype of the output tensor. Default: `torch.float32`

    Returns:
        beta * K * K^T of shape `[B, T, H, BT]` where `BT` is the chunk size.
    """

    B, T, Hg, K = k.shape

    H = beta.shape[-1]
    BT = chunk_size
    chunk_indices = prepare_chunk_indices(
        cu_seqlens, BT) if cu_seqlens is not None else None
    NT = triton.cdiv(T, BT) if cu_seqlens is None else len(chunk_indices)
    A = torch.empty(B, T, H, BT, device=k.device, dtype=output_dtype)
    chunk_scaled_dot_kkt_fwd_kernel[(NT, B * H)](
        k=k,
        beta=beta,
        g_cumsum=g_cumsum,
        A=A,
        cu_seqlens=cu_seqlens,
        chunk_indices=chunk_indices,
        T=T,
        H=H,
        Hg=Hg,
        K=K,
        BT=BT,
    )
    return A
