#pragma once
#include <float.h>
#include <torch/extension.h>
#include <c10/cuda/CUDAGuard.h>
#include "attn_common.h"
#include "attn_warp_utils.cuh"

using bf16 = __nv_bfloat16;

// Dispatch head_dim: shared macro — avoids C++20 lambda template syntax.
// Usage: DISPATCH_HEAD_DIM(hd, fn, args...)
//   Expands to: fn<32>(args...); fn<64>(args...); etc.
#define DISPATCH_HEAD_DIM(hd, fn, ...) \
    switch (hd) { \
        case 32:  fn<32>(__VA_ARGS__); break; \
        case 64:  fn<64>(__VA_ARGS__); break; \
        case 128: fn<128>(__VA_ARGS__); break; \
        case 256: fn<256>(__VA_ARGS__); break; \
        default: \
            TORCH_CHECK(false, "unsupported head_dim ", hd, \
                         " (supported: 32, 64, 128, 256)"); \
    }

// The split kernel unconditionally writes every (batch, q_head, split) slot it
// owns — including empty split ranges, which store m = -FLT_MAX so the combine
// skips them. Allocators are therefore left uninitialized (torch::empty); the
// per-call memset (torch::zeros / torch::full) was pure overhead.
template<typename P>
inline void alloc_split_partials(P& p) {
    auto fopt = torch::TensorOptions().dtype(torch::kFloat32).device(torch::kCUDA);
    auto o_part = torch::empty(at::IntArrayRef{p.batch, p.q_head, MAX_SPLITS, p.head_dim}, fopt);
    auto ml_part = torch::empty(at::IntArrayRef{p.batch, p.q_head, MAX_SPLITS, 2}, fopt);
    p.o_part = (float*)o_part.data_ptr();
    p.ml_part = (float*)ml_part.data_ptr();
}

// ---- Shared Q-dims + strides extraction ----
template <typename P>
inline void extract_q_dims_and_strides(torch::Tensor& q, int64_t layout, P& p) {
    if (layout == BLHD) q = q.transpose(1, 2);
    p.batch = (int)q.size(0);
    p.q_head = (int)q.size(1);
    p.q_len = (int)q.size(2);
    p.head_dim = (int)q.size(3);
    p.q_stride_b = (int)q.stride(0);
    p.q_stride_h = (int)q.stride(1);
    p.q_stride_l = (int)q.stride(2);
    p.q_stride_d = (int)q.stride(3);
}

// ---- Shared mask packing ----
// Accepts 2D [batch, kv_len], 3D [batch, q_len, kv_len],
// or 4D [batch, n_heads, q_len, kv_len].
// Head/q dimensions with size 1 broadcast (stride set to 0).
template <typename P>
inline void pack_mask(const c10::optional<torch::Tensor>& mask, P& p) {
    if (p.use_mask) {
        auto m = mask.value();
        TORCH_CHECK(m.is_cuda(), "mask must be on CUDA");
        TORCH_CHECK(m.dtype() == torch::kBool, "mask must be bool");
        TORCH_CHECK(m.size(0) == p.batch, "mask batch mismatch");
        TORCH_CHECK(m.size(m.dim() - 1) == p.kv_len, "mask kv_len mismatch");
        if (m.dim() == 2) {
            p.mask_b_stride = (int)m.stride(0);
            p.mask_h_stride = 0;
            p.mask_q_stride = 0;
        } else if (m.dim() == 3) {
            TORCH_CHECK(m.size(1) == 1 || m.size(1) == p.q_len, "mask q_len mismatch");
            p.mask_b_stride = (int)m.stride(0);
            p.mask_h_stride = 0;
            p.mask_q_stride = (m.size(1) == 1) ? 0 : (int)m.stride(1);
        } else if (m.dim() == 4) {
            TORCH_CHECK(m.size(2) == 1 || m.size(2) == p.q_len, "mask q_len mismatch");
            p.mask_b_stride = (int)m.stride(0);
            p.mask_h_stride = (m.size(1) == 1) ? 0 : (int)m.stride(1);
            p.mask_q_stride = (m.size(2) == 1) ? 0 : (int)m.stride(2);
        } else {
            TORCH_CHECK(false, "mask must be 2D, 3D, or 4D");
        }
        p.mask = m.data_ptr<bool>();
    } else {
        p.mask = nullptr;
        p.mask_b_stride = 0;
        p.mask_h_stride = 0;
        p.mask_q_stride = 0;
    }
}

// ---- attn_pack_params (contiguous KV) ----
template<typename T>
inline void attn_pack_params(
    torch::Tensor q,
    torch::Tensor k,
    torch::Tensor v,
    c10::optional<torch::Tensor> mask,
    int64_t causal_offset,
    double scale,
    int64_t layout,
    AttentionParams<T>& p
) {
    const at::cuda::OptionalCUDAGuard device_guard(device_of(q));

    TORCH_CHECK(q.is_cuda() && k.is_cuda() && v.is_cuda());
    TORCH_CHECK(q.dtype() == torch::kBFloat16);
    TORCH_CHECK(k.dtype() == torch::kBFloat16);
    TORCH_CHECK(v.dtype() == torch::kBFloat16);
    TORCH_CHECK(k.sizes() == v.sizes(), "K and V must have identical shapes");
    TORCH_CHECK(q.dim() == 4 && k.dim() == 4, "Q/K/V must be 4D");
    extract_q_dims_and_strides(q, layout, p);

    if (layout == BLHD) k = k.transpose(1, 2), v = v.transpose(1, 2);

    p.kv_head = (int)k.size(1);
    p.kv_len = (int)k.size(2);
    TORCH_CHECK(p.q_head % p.kv_head == 0,
                "q_head must be divisible by kv_head");
    TORCH_CHECK(k.size(3) == p.head_dim, "K/V head_dim must match Q");
    TORCH_CHECK(q.stride(3) == 1 && k.stride(3) == 1 && v.stride(3) == 1,
                "Q/K/V head_dim must be contiguous");

    p.kv_stride_b = (int)k.stride(0);
    p.kv_stride_h = (int)k.stride(1);
    p.kv_stride_l = (int)k.stride(2);
    p.kv_stride_d = (int)k.stride(3);

    p.causal_offset = (int)causal_offset;
    p.use_mask = mask.has_value() ? 1 : 0;
    p.scale = (scale > 0.0) ? (float)scale : 1.0f / sqrtf((float)p.head_dim);

    p.q = (const T*)q.data_ptr();
    p.k = (const T*)k.data_ptr();
    p.v = (const T*)v.data_ptr();
    p.o = nullptr;
    p.o_part = nullptr;
    p.ml_part = nullptr;

    pack_mask(mask, p);
}

// ---- attn_pack_paged_decode_params ----
// SGLang-style: flat KV pool + req_to_token indexing + variable
// seq_lens via kv_indptr.  Q is [batch, q_head, head_dim] (q_len=1 per req).
template<typename T>
inline void attn_pack_paged_decode_params(
    torch::Tensor q,
    torch::Tensor k_cache,
    torch::Tensor v_cache,
    torch::Tensor req_to_token,
    torch::Tensor req_pool_indices,
    torch::Tensor kv_indptr,
    int64_t max_seq_len,
    c10::optional<torch::Tensor> mask,
    int64_t causal_offset,
    double scale,
    AttentionParams<T>& p
) {
    const at::cuda::OptionalCUDAGuard device_guard(device_of(q));

    TORCH_CHECK(q.is_cuda() && k_cache.is_cuda() && v_cache.is_cuda());
    TORCH_CHECK(req_to_token.is_cuda() && req_pool_indices.is_cuda() && kv_indptr.is_cuda());
    TORCH_CHECK(q.dtype() == torch::kBFloat16, "q must be bf16");
    TORCH_CHECK(k_cache.dtype() == torch::kBFloat16, "k_cache must be bf16");
    TORCH_CHECK(v_cache.dtype() == torch::kBFloat16, "v_cache must be bf16");
    TORCH_CHECK(req_to_token.dtype() == torch::kLong, "req_to_token must be int64");
    TORCH_CHECK(req_pool_indices.dtype() == torch::kLong, "req_pool_indices must be int64");
    TORCH_CHECK(kv_indptr.dtype() == torch::kInt32, "kv_indptr must be int32");
    TORCH_CHECK(k_cache.sizes() == v_cache.sizes(), "k_cache and v_cache must match");
    TORCH_CHECK(k_cache.dim() == 3, "k_cache must be 3D [size, kv_head, head_dim]");
    TORCH_CHECK(q.dim() == 3, "q must be 3D [batch, q_head, head_dim]");

    p.batch = (int)q.size(0);
    p.q_head = (int)q.size(1);
    p.head_dim = (int)q.size(2);
    p.kv_head = (int)k_cache.size(1);
    TORCH_CHECK(k_cache.size(2) == p.head_dim, "k_cache head_dim mismatch");
    TORCH_CHECK(q.stride(2) == 1 && k_cache.stride(2) == 1 && v_cache.stride(2) == 1,
                "Q/K/V head_dim must be contiguous");
    TORCH_CHECK(p.head_dim % 32 == 0, "head_dim must be multiple of 32");
    TORCH_CHECK(p.q_head % p.kv_head == 0, "q_head must be divisible by kv_head");

    p.q_stride_l = (int)q.stride(0);
    p.q_stride_h = (int)q.stride(1);
    p.q_stride_d = (int)q.stride(2);

    p.k_cache = (const T*)k_cache.data_ptr();
    p.v_cache = (const T*)v_cache.data_ptr();
    p.q = (const T*)q.data_ptr();
    p.req_to_token = req_to_token.data_ptr<int64_t>();
    p.req_pool_indices = req_pool_indices.data_ptr<int64_t>();
    p.kv_indptr = kv_indptr.data_ptr<int>();
    p.qo_indptr = nullptr;
    p.max_context_len = (int)req_to_token.size(1);
    p.max_seq_len = (int)max_seq_len;
    p.total_q = p.batch;  // decode: 1 Q token per request
    p.max_q_len = 1;

    p.causal_offset = (int)causal_offset;
    p.use_mask = (mask.has_value() && mask.value().defined()) ? 1 : 0;
    p.scale = (scale > 0.0) ? (float)scale : 1.0f / sqrtf((float)p.head_dim);

    if (p.use_mask) {
        auto m = mask.value();
        TORCH_CHECK(m.is_cuda() && m.dtype() == torch::kBool, "mask must be bool CUDA");
        TORCH_CHECK(m.size(0) == p.batch, "mask batch mismatch");
        p.mask_b_stride = (int)m.stride(0);
        p.mask_h_stride = 0;
        p.mask_q_stride = 0;
        p.mask = m.data_ptr<bool>();
    } else {
        p.mask = nullptr;
        p.mask_b_stride = 0;
        p.mask_h_stride = 0;
        p.mask_q_stride = 0;
    }

    p.o = nullptr;
    p.o_part = nullptr;
    p.ml_part = nullptr;
}

// ---- attn_pack_paged_prefill_params ----
// SGLang-style: flat KV pool + req_to_token + ragged batch via qo_indptr.
// Q is [total_q, q_head, head_dim] (flattened across all requests).
template<typename T>
inline void attn_pack_paged_prefill_params(
    torch::Tensor q,
    torch::Tensor k_cache,
    torch::Tensor v_cache,
    torch::Tensor req_to_token,
    torch::Tensor req_pool_indices,
    torch::Tensor kv_indptr,
    torch::Tensor qo_indptr,
    c10::optional<torch::Tensor> mask,
    int64_t max_q_len,
    int64_t causal_offset,
    double scale,
    AttentionParams<T>& p
) {
    const at::cuda::OptionalCUDAGuard device_guard(device_of(q));

    TORCH_CHECK(q.is_cuda() && k_cache.is_cuda() && v_cache.is_cuda());
    TORCH_CHECK(req_to_token.is_cuda() && req_pool_indices.is_cuda());
    TORCH_CHECK(kv_indptr.is_cuda() && qo_indptr.is_cuda());
    TORCH_CHECK(q.dtype() == torch::kBFloat16, "q must be bf16");
    TORCH_CHECK(k_cache.dtype() == torch::kBFloat16, "k_cache must be bf16");
    TORCH_CHECK(v_cache.dtype() == torch::kBFloat16, "v_cache must be bf16");
    TORCH_CHECK(req_to_token.dtype() == torch::kLong, "req_to_token must be int64");
    TORCH_CHECK(req_pool_indices.dtype() == torch::kLong, "req_pool_indices must be int64");
    TORCH_CHECK(kv_indptr.dtype() == torch::kInt32, "kv_indptr must be int32");
    TORCH_CHECK(qo_indptr.dtype() == torch::kInt32, "qo_indptr must be int32");
    TORCH_CHECK(k_cache.sizes() == v_cache.sizes(), "k_cache and v_cache must match");
    TORCH_CHECK(k_cache.dim() == 3, "k_cache must be 3D [size, kv_head, head_dim]");
    TORCH_CHECK(q.dim() == 3, "q must be 3D [total_q, q_head, head_dim]");

    p.q_head = (int)q.size(1);
    p.head_dim = (int)q.size(2);
    p.kv_head = (int)k_cache.size(1);
    p.batch = (int)req_pool_indices.size(0);
    TORCH_CHECK(k_cache.size(2) == p.head_dim, "k_cache head_dim mismatch");
    TORCH_CHECK(q.stride(2) == 1 && k_cache.stride(2) == 1 && v_cache.stride(2) == 1,
                "Q/K/V head_dim must be contiguous");
    TORCH_CHECK(p.head_dim % 16 == 0, "head_dim must be multiple of 16");
    TORCH_CHECK(p.q_head % p.kv_head == 0, "q_head must be divisible by kv_head");
    TORCH_CHECK(kv_indptr.size(0) == p.batch + 1, "kv_indptr must be [batch+1]");
    TORCH_CHECK(qo_indptr.size(0) == p.batch + 1, "qo_indptr must be [batch+1]");

    p.q_stride_l = (int)q.stride(0);
    p.q_stride_h = (int)q.stride(1);
    p.q_stride_d = (int)q.stride(2);

    p.k_cache = (const T*)k_cache.data_ptr();
    p.v_cache = (const T*)v_cache.data_ptr();
    p.q = (const T*)q.data_ptr();
    p.req_to_token = req_to_token.data_ptr<int64_t>();
    p.req_pool_indices = req_pool_indices.data_ptr<int64_t>();
    p.kv_indptr = kv_indptr.data_ptr<int>();
    p.qo_indptr = qo_indptr.data_ptr<int>();
    p.max_context_len = (int)req_to_token.size(1);
    p.total_q = (int)q.size(0);  // prefill: flattened Q across all requests
    p.max_q_len = (int)max_q_len;
    // max_seq_len is unused by the prefill path (decode uses it for split
    // computation); fill with max_q_len only to keep the POD struct defined.
    p.max_seq_len = p.max_q_len;

    p.causal_offset = (int)causal_offset;
    p.use_mask = (mask.has_value() && mask.value().defined()) ? 1 : 0;
    if (p.use_mask) {
        auto m = mask.value();
        TORCH_CHECK(m.is_cuda() && m.dtype() == torch::kBool, "mask must be bool CUDA");
        TORCH_CHECK(m.size(0) == p.batch, "mask batch mismatch");
        if (m.dim() == 2) {
            TORCH_CHECK(m.size(1) <= p.max_context_len, "mask kv_len mismatch");
            p.mask_b_stride = (int)m.stride(0);
            p.mask_h_stride = 0;
            p.mask_q_stride = 0;
        } else if (m.dim() == 4) {
            TORCH_CHECK(m.size(1) == 1 || m.size(1) == p.q_head, "mask head mismatch");
            TORCH_CHECK(m.size(2) == 1 || m.size(2) == p.max_q_len, "mask q_len mismatch");
            TORCH_CHECK(m.size(3) <= p.max_context_len, "mask kv_len mismatch");
            p.mask_b_stride = (int)m.stride(0);
            p.mask_h_stride = (m.size(1) == 1) ? 0 : (int)m.stride(1);
            p.mask_q_stride = (m.size(2) == 1) ? 0 : (int)m.stride(2);
        } else {
            TORCH_CHECK(false, "mask must be 2D or 4D");
        }
        p.mask = m.data_ptr<bool>();
    } else {
        p.mask = nullptr;
        p.mask_b_stride = 0;
        p.mask_h_stride = 0;
        p.mask_q_stride = 0;
    }
    p.scale = (scale > 0.0) ? (float)scale : 1.0f / sqrtf((float)p.head_dim);

    p.o = nullptr;
    p.o_part = nullptr;
    p.ml_part = nullptr;
}