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 // SPDX-License-Identifier: MIT
 // Copyright (c) 2018-2025, Advanced Micro Devices, Inc. All rights reserved.
  
 #pragma once
  
 namespace ck_tile {
  
 template <typename FmhaPipeline_, typename EpiloguePipeline_>
 struct FmhaFwdSplitKVCombineKernel
 {
     using FmhaPipeline     = remove_cvref_t<FmhaPipeline_>;
     using EpiloguePipeline = remove_cvref_t<EpiloguePipeline_>;
  
     static constexpr index_t kNumWarps   = FmhaPipeline::kNumWarps;
     static constexpr index_t kBlockSize  = FmhaPipeline::kBlockSize;
     static constexpr index_t kBlockPerCu = FmhaPipeline::kBlockPerCu;
  
     static_assert(kBlockPerCu > 0);
     static constexpr index_t kBlockPerCuInput = FmhaPipeline::Problem::kBlockPerCu;
  
     using LSEDataType  = remove_cvref_t<typename FmhaPipeline::LSEDataType>;
     using OaccDataType = remove_cvref_t<typename FmhaPipeline::OaccDataType>;
     using ODataType    = remove_cvref_t<typename FmhaPipeline::ODataType>;
  
     static constexpr bool kIsGroupMode      = FmhaPipeline::kIsGroupMode;
     static constexpr bool kPadSeqLenQ       = FmhaPipeline::kPadSeqLenQ;
     static constexpr bool kPadHeadDimV      = FmhaPipeline::kPadHeadDimV;
     static constexpr bool kStoreLSE         = FmhaPipeline::kStoreLSE;
     static constexpr bool kDoFp8StaticQuant = FmhaPipeline::Problem::kDoFp8StaticQuant;
  
     // clang-format off
     template <typename T> struct t2s;
     template <> struct t2s<float> { static constexpr const char * name = "fp32"; };
     template <> struct t2s<ck_tile::fp16_t> { static constexpr const char * name = "fp16"; };
     template <> struct t2s<ck_tile::bf16_t> { static constexpr const char * name = "bf16"; };
     template <> struct t2s<ck_tile::fp8_t> { static constexpr const char * name = "fp8"; };
     template <> struct t2s<ck_tile::bf8_t> { static constexpr const char * name = "bf8"; };
     // clang-format on
  
     __host__ static std::string GetName()
     {
         // sync with generate.py
         // clang-format off
  
         #define _SS_  std::string
         #define _TS_  std::to_string
         auto pn = [&] () {
             std::string n;
             if (kPadSeqLenQ) n += "s";
             if (kPadHeadDimV) n += "dv";
             return n.empty() ? n : std::string("p") + n; }();
         return
             _SS_("fmha_fwd_splitkv_combine_d") + _TS_(FmhaPipeline::kHeadDimV) + "_" + _SS_(t2s<ODataType>::name) +
             "_" + (kIsGroupMode ? "group" : "batch") + "_"
             "b" + _TS_(FmhaPipeline::kN1) + "_" +
             (kBlockPerCuInput == -1 ? "" : ("o" + _TS_(kBlockPerCu) + "_")) +
             _SS_(FmhaPipeline::name) +
             (pn.empty() ? "_npad" : "_" + pn) +
             (kStoreLSE ? "_lse" : "_nlse" ) +
             (kDoFp8StaticQuant ? "_squant" : "_nsquant" );
         #undef _SS_
         #undef _TS_
         // clang-format on
     }
  
     template <ck_tile::index_t I> // to avoid duplicated base class prblem, introduce an template
                                   // arg
     struct EmptyKargs
     {
     };
  
     // kargs use aggregate initializer, so no constructor will provided
     // use inheritance to minimize karg size
     // user need to use MakeKargs() function to create kargs.
     struct CommonKargs
     {
         const void* lse_acc_ptr;
         const void* o_acc_ptr;
         void* o_ptr;
  
         ck_tile::index_t batch;
         ck_tile::index_t seqlen_q;
         ck_tile::index_t hdim_v;
         ck_tile::index_t num_splits;
  
         ck_tile::index_t row_stride_o_acc;
         ck_tile::index_t row_stride_o;
  
         ck_tile::index_t nhead_stride_lse_acc;
         ck_tile::index_t nhead_stride_o_acc;
         ck_tile::index_t nhead_stride_o;
  
         ck_tile::index_t split_stride_lse_acc;
         ck_tile::index_t split_stride_o_acc;
     };
  
     struct CommonLSEKargs
     {
         void* lse_ptr                     = nullptr;
         ck_tile::index_t nhead_stride_lse = 0;
         ck_tile::index_t batch_stride_lse = 0;
     };
  
     struct Fp8StaticQuantKargs
     {
         float scale_o;
     };
  
     struct BatchModeKargs
         : CommonKargs,
           std::conditional_t<kStoreLSE, CommonLSEKargs, EmptyKargs<0>>,
           std::conditional_t<kDoFp8StaticQuant, Fp8StaticQuantKargs, EmptyKargs<1>>
     {
         ck_tile::index_t batch_stride_lse_acc;
         ck_tile::index_t batch_stride_o_acc;
         ck_tile::index_t batch_stride_o;
     };
  
     struct GroupModeKargs
         : CommonKargs,
           std::conditional_t<kStoreLSE, CommonLSEKargs, EmptyKargs<0>>,
           std::conditional_t<kDoFp8StaticQuant, Fp8StaticQuantKargs, EmptyKargs<3>>
     {
         const int32_t* seqstart_q_ptr;
     };
  
     using Kargs = std::conditional_t<kIsGroupMode, GroupModeKargs, BatchModeKargs>;
  
     template <bool Cond = !kIsGroupMode>
     __host__ static constexpr std::enable_if_t<Cond, Kargs>
     MakeKargs(const void* lse_acc_ptr,
               const void* o_acc_ptr,
               void* lse_ptr,
               void* o_ptr,
               ck_tile::index_t batch,
               ck_tile::index_t seqlen_q,
               ck_tile::index_t hdim_v,
               ck_tile::index_t num_splits,
               float scale_o,
               ck_tile::index_t row_stride_o_acc,
               ck_tile::index_t row_stride_o,
               ck_tile::index_t nhead_stride_lse_acc,
               ck_tile::index_t nhead_stride_o_acc,
               ck_tile::index_t nhead_stride_lse,
               ck_tile::index_t nhead_stride_o,
               ck_tile::index_t batch_stride_lse_acc,
               ck_tile::index_t batch_stride_o_acc,
               ck_tile::index_t batch_stride_lse,
               ck_tile::index_t batch_stride_o,
               ck_tile::index_t split_stride_lse_acc,
               ck_tile::index_t split_stride_o_acc)
     {
         Kargs kargs{{lse_acc_ptr,
                      o_acc_ptr,
                      o_ptr,
                      batch,
                      seqlen_q,
                      hdim_v,
                      num_splits,
                      row_stride_o_acc,
                      row_stride_o,
                      nhead_stride_lse_acc,
                      nhead_stride_o_acc,
                      nhead_stride_o,
                      split_stride_lse_acc,
                      split_stride_o_acc}, // args for common karg
                     {},                   // placeholder for lse
                     {},                   // placeholder for fp8_static_quant args
                     batch_stride_lse_acc,
                     batch_stride_o_acc,
                     batch_stride_o};
  
         if constexpr(kStoreLSE)
         {
             kargs.lse_ptr          = lse_ptr;
             kargs.nhead_stride_lse = nhead_stride_lse;
             kargs.batch_stride_lse = batch_stride_lse;
         }
         if constexpr(kDoFp8StaticQuant)
         {
             kargs.scale_o = scale_o;
         }
  
         return kargs;
     }
  
     template <bool Cond = kIsGroupMode>
     __host__ static constexpr std::enable_if_t<Cond, Kargs>
     MakeKargs(const void* lse_acc_ptr,
               const void* o_acc_ptr,
               void* lse_ptr,
               void* o_ptr,
               ck_tile::index_t batch,
               const void* seqstart_q_ptr,
               ck_tile::index_t hdim_v,
               ck_tile::index_t num_splits,
               float scale_o,
               ck_tile::index_t row_stride_o_acc,
               ck_tile::index_t row_stride_o,
               ck_tile::index_t nhead_stride_lse_acc,
               ck_tile::index_t nhead_stride_o_acc,
               ck_tile::index_t nhead_stride_lse,
               ck_tile::index_t nhead_stride_o,
               ck_tile::index_t split_stride_lse_acc,
               ck_tile::index_t split_stride_o_acc)
     {
         Kargs kargs{{lse_acc_ptr,
                      o_acc_ptr,
                      o_ptr,
                      batch,
                      -1, // seqlen will be updated by another pointer
                      hdim_v,
                      num_splits,
                      row_stride_o_acc,
                      row_stride_o,
                      nhead_stride_lse_acc,
                      nhead_stride_o_acc,
                      nhead_stride_o,
                      split_stride_lse_acc,
                      split_stride_o_acc}, // args for common karg
                     {},                   // placeholder for lse
                     {},                   // placeholder for fp8_static_quant args
                     reinterpret_cast<const int32_t*>(seqstart_q_ptr)};
  
         if constexpr(kStoreLSE)
         {
             kargs.lse_ptr          = lse_ptr;
             kargs.nhead_stride_lse = nhead_stride_lse;
         }
         if constexpr(kDoFp8StaticQuant)
         {
             kargs.scale_o = scale_o;
         }
  
         return kargs;
     }
  
     CK_TILE_HOST static constexpr auto GridSize(ck_tile::index_t batch_size,
                                                 ck_tile::index_t nhead,
                                                 ck_tile::index_t max_seqlen_q,
                                                 ck_tile::index_t hdim_v)
     {
         // TODO: this may need tuning
         return dim3(ck_tile::integer_divide_ceil(max_seqlen_q, FmhaPipeline::kM0) *
                         ck_tile::integer_divide_ceil(hdim_v, FmhaPipeline::kN1),
                     nhead,
                     batch_size);
     }
  
     CK_TILE_DEVICE static constexpr auto GetTileIndex(const Kargs& kargs)
     {
         const index_t num_tile_n1 = ck_tile::integer_divide_ceil(kargs.hdim_v, FmhaPipeline::kN1);
  
         const index_t i_block = blockIdx.x;
         const index_t i_nhead = blockIdx.y;
         const index_t i_batch = blockIdx.z;
  
         const auto f = [](index_t dividend, index_t divisor) {
             index_t quotient = dividend / divisor;
             index_t modulus  = dividend - quotient * divisor;
             return ck_tile::make_tuple(quotient, modulus);
         };
  
         const auto [i_tile_m, i_tile_n] = f(i_block, num_tile_n1);
  
         return ck_tile::make_tuple(i_tile_m, i_tile_n, i_nhead, i_batch);
     }
  
     __host__ static constexpr auto BlockSize() { return dim3(kBlockSize); }
  
     CK_TILE_HOST_DEVICE static constexpr ck_tile::index_t GetSmemSize()
     {
         return ck_tile::max(FmhaPipeline::GetSmemSize(), EpiloguePipeline::GetSmemSize());
     }
  
     CK_TILE_DEVICE void operator()(Kargs kargs) const
     {
         // allocate LDS
         __shared__ char smem_ptr[GetSmemSize()];
  
         // divide problem
         const auto [i_tile_m, i_tile_n, i_nhead, i_batch] = GetTileIndex(kargs);
  
         const index_t i_m0 = __builtin_amdgcn_readfirstlane(i_tile_m * FmhaPipeline::kM0);
         const index_t i_n1 = __builtin_amdgcn_readfirstlane(i_tile_n * FmhaPipeline::kN1);
  
         long_index_t batch_offset_lse_acc = 0;
         long_index_t batch_offset_o_acc   = 0;
         long_index_t batch_offset_lse     = 0;
         long_index_t batch_offset_o       = 0;
  
         if constexpr(kIsGroupMode)
         {
             // get starting offset for each batch
             const long_index_t query_start = kargs.seqstart_q_ptr[i_batch];
  
             batch_offset_lse_acc = query_start;
             batch_offset_o_acc   = query_start * kargs.row_stride_o_acc;
  
             if constexpr(kStoreLSE)
             {
                 batch_offset_lse = query_start;
             }
  
             batch_offset_o = query_start * kargs.row_stride_o;
  
             // get real # queries & # keys under group mode
             const auto adjusted_seqstart_q_ptr = kargs.seqstart_q_ptr + i_batch;
             kargs.seqlen_q = adjusted_seqstart_q_ptr[1] - adjusted_seqstart_q_ptr[0];
  
             // # of required blocks is different in each groups, terminate unnecessary blocks
             // earlier
             if(kargs.seqlen_q <= i_m0)
             {
                 return;
             }
         }
         else
         {
             batch_offset_lse_acc = static_cast<long_index_t>(i_batch) * kargs.batch_stride_lse_acc;
             batch_offset_o_acc   = static_cast<long_index_t>(i_batch) * kargs.batch_stride_o_acc;
  
             if constexpr(kStoreLSE)
             {
                 batch_offset_lse = static_cast<long_index_t>(i_batch) * kargs.batch_stride_lse;
             }
  
             batch_offset_o = static_cast<long_index_t>(i_batch) * kargs.batch_stride_o;
         }
  
         // for simplicity, batch stride we just modify the pointer
         const LSEDataType* lse_acc_ptr =
             reinterpret_cast<const LSEDataType*>(kargs.lse_acc_ptr) +
             static_cast<long_index_t>(i_nhead) * kargs.nhead_stride_lse_acc + batch_offset_lse_acc;
         const OaccDataType* o_acc_ptr =
             reinterpret_cast<const OaccDataType*>(kargs.o_acc_ptr) +
             static_cast<long_index_t>(i_nhead) * kargs.nhead_stride_o_acc + batch_offset_o_acc;
         ODataType* o_ptr = reinterpret_cast<ODataType*>(kargs.o_ptr) +
                            static_cast<long_index_t>(i_nhead) * kargs.nhead_stride_o +
                            batch_offset_o;
  
         // LSEacc/Oacc DRAM and DRAM windows
         const auto lse_acc_dram = [&]() {
             const auto lse_acc_dram_naive = make_naive_tensor_view<address_space_enum::global>(
                 lse_acc_ptr,
                 make_tuple(kargs.num_splits, kargs.seqlen_q),
                 make_tuple(kargs.split_stride_lse_acc, 1),
                 number<FmhaPipeline::kAlignmentLSEacc>{},
                 number<1>{});
  
             return pad_tensor_view(
                 lse_acc_dram_naive,
                 make_tuple(number<FmhaPipeline::kMaxSplits>{}, number<FmhaPipeline::kM0>{}),
                 sequence<true, kPadSeqLenQ>{});
         }();
  
         auto o_acc_dram = [&]() {
             const auto o_acc_dram_naive = make_naive_tensor_view<address_space_enum::global>(
                 o_acc_ptr,
                 make_tuple(kargs.num_splits, kargs.seqlen_q, kargs.hdim_v),
                 make_tuple(kargs.split_stride_o_acc, kargs.row_stride_o_acc, 1),
                 number<FmhaPipeline::kAlignmentOacc>{},
                 number<1>{});
  
             // read 4 * (kM0, kN1) o_acc tiles simultaneously by 4 warps
             const auto o_acc_dram_view = pad_tensor_view(
                 o_acc_dram_naive,
                 make_tuple(
                     number<kNumWarps>{}, number<FmhaPipeline::kM0>{}, number<FmhaPipeline::kN1>{}),
                 sequence<true, kPadSeqLenQ, kPadHeadDimV>{});
  
             const index_t padded_num_splits =
                 o_acc_dram_view.get_tensor_descriptor().get_lengths()[number<0>{}];
             const index_t padded_seqlen_q =
                 o_acc_dram_view.get_tensor_descriptor().get_lengths()[number<1>{}];
             const index_t padded_hdim_v =
                 o_acc_dram_view.get_tensor_descriptor().get_lengths()[number<2>{}];
  
             const index_t num_m_tiles = integer_divide_floor(padded_seqlen_q, FmhaPipeline::kM0);
  
             // transform tensor view by following steps, given shape: (padded_num_splits,
             // padded_seqlen_q, padded_hdim_v)
             //     1. unmerge to (padded_num_splits, num_m_tiles, kM0, padded_hdim_v)
             //     2. transpose to (num_m_tiles, padded_num_splits, kM0, padded_hdim_v)
             //     3. merge to (num_m_tiles * padded_num_splits * kM0, padded_hdim_v)
             auto transposed = transform_tensor_view(
                 o_acc_dram_view,
                 make_tuple(make_pass_through_transform(padded_num_splits),
                            make_unmerge_transform(make_tuple(num_m_tiles, FmhaPipeline::kM0)),
                            make_pass_through_transform(padded_hdim_v)),
                 make_tuple(sequence<0>{}, sequence<1>{}, sequence<2>{}),
                 make_tuple(sequence<1>{}, sequence<0, 2>{}, sequence<3>{}));
  
             return transform_tensor_view(
                 transposed,
                 make_tuple(make_merge_transform(
                                make_tuple(num_m_tiles, padded_num_splits, FmhaPipeline::kM0)),
                            make_pass_through_transform(padded_hdim_v)),
                 make_tuple(sequence<0, 1, 2>{}, sequence<3>{}),
                 make_tuple(sequence<0>{}, sequence<1>{}));
         }();
  
         auto lse_acc_dram_window = make_tile_window(
             lse_acc_dram,
             make_tuple(number<FmhaPipeline::kMaxSplits>{}, number<FmhaPipeline::kM0>{}),
             {0, i_m0});
  
         const index_t padded_num_splits =
             integer_divide_ceil(kargs.num_splits, kNumWarps) * kNumWarps;
  
         auto o_acc_dram_window = make_tile_window(
             o_acc_dram,
             make_tuple(number<kNumWarps * FmhaPipeline::kM0>{}, number<FmhaPipeline::kN1>{}),
             {i_tile_m * padded_num_splits * FmhaPipeline::kM0, i_n1});
  
         // LSE DRAM window
         auto lse_dram_window = [&, i_nhead_ = i_nhead]() {
             constexpr auto lse_dram_window_lengths = make_tuple(number<FmhaPipeline::kM0>{});
             if constexpr(kStoreLSE)
             {
                 LSEDataType* lse_ptr =
                     reinterpret_cast<LSEDataType*>(kargs.lse_ptr) +
                     static_cast<long_index_t>(i_nhead_) * kargs.nhead_stride_lse + batch_offset_lse;
  
                 const auto lse_dram = [&]() {
                     const auto lse_dram_naive = make_naive_tensor_view<address_space_enum::global>(
                         lse_ptr,
                         make_tuple(kargs.seqlen_q),
                         make_tuple(1),
                         number<FmhaPipeline::kAlignmentLSE>{},
                         number<1>{});
  
                     return pad_tensor_view(
                         lse_dram_naive, lse_dram_window_lengths, sequence<kPadSeqLenQ>{});
                 }();
  
                 return make_tile_window(lse_dram, lse_dram_window_lengths, {i_m0});
             }
             else
             {
                 return make_null_tile_window(lse_dram_window_lengths);
             }
         }();
  
         auto o_acc_tile = [&]() {
             if constexpr(kDoFp8StaticQuant)
             {
                 return FmhaPipeline{}(
                     lse_acc_dram_window,
                     o_acc_dram_window,
                     lse_dram_window,
                     identity{},                                          // lse_element_func
                     composes(saturates<fp8_t>{}, scales{kargs.scale_o}), // o_acc_element_func
                     kargs.num_splits,
                     smem_ptr);
             }
             else
             {
                 return FmhaPipeline{}(lse_acc_dram_window,
                                       o_acc_dram_window,
                                       lse_dram_window,
                                       kargs.num_splits,
                                       smem_ptr);
             }
         }();
  
         // O DRAM and DRAM window
         auto o_dram = [&]() {
             const auto o_dram_naive = make_naive_tensor_view<address_space_enum::global>(
                 o_ptr,
                 make_tuple(kargs.seqlen_q, kargs.hdim_v),
                 make_tuple(kargs.row_stride_o, 1),
                 number<FmhaPipeline::kAlignmentO>{},
                 number<1>{});
  
             return pad_tensor_view(
                 o_dram_naive,
                 make_tuple(number<FmhaPipeline::kM0>{}, number<FmhaPipeline::kN1>{}),
                 sequence<kPadSeqLenQ, kPadHeadDimV>{});
         }();
  
         auto o_dram_window =
             make_tile_window(o_dram,
                              make_tuple(number<FmhaPipeline::kM0>{}, number<FmhaPipeline::kN1>{}),
                              {i_m0, i_n1});
  
         EpiloguePipeline{}(o_dram_window, o_acc_tile, nullptr);
     }
 };
  
 } // namespace ck_tile