/* Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License. */

#pragma once

#ifdef __NVCC__

#include <cub/cub.cuh>
#include <limits>
#include <string>
#include <typeinfo>
#include <vector>
#include "paddle/fluid/framework/ddim.h"
#include "paddle/fluid/framework/tensor.h"
#include "paddle/fluid/operators/transpose_op.h"
#include "paddle/fluid/platform/device_context.h"

namespace paddle {
namespace operators {

namespace {  // NOLINT
template <typename K, typename V>
using KeyValuePair = cub::KeyValuePair<K, V>;
using Tensor = framework::Tensor;

}  // end namespace

#define FIXED_BLOCK_DIM_CASE_BASE(log2_block_dim, ...)  \
  case (1 << (log2_block_dim)): {                       \
    constexpr auto kBlockDim = (1 << (log2_block_dim)); \
    __VA_ARGS__;                                        \
  } break

#define FIXED_BLOCK_DIM_CASE(...)               \
  FIXED_BLOCK_DIM_CASE_BASE(10, ##__VA_ARGS__); \
  FIXED_BLOCK_DIM_CASE_BASE(9, ##__VA_ARGS__);  \
  FIXED_BLOCK_DIM_CASE_BASE(8, ##__VA_ARGS__);  \
  FIXED_BLOCK_DIM_CASE_BASE(7, ##__VA_ARGS__);  \
  FIXED_BLOCK_DIM_CASE_BASE(6, ##__VA_ARGS__);  \
  FIXED_BLOCK_DIM_CASE_BASE(5, ##__VA_ARGS__);  \
  FIXED_BLOCK_DIM_CASE_BASE(4, ##__VA_ARGS__);  \
  FIXED_BLOCK_DIM_CASE_BASE(3, ##__VA_ARGS__);

template <typename T, typename IndType, class Reducer, size_t BlockDim>
__global__ void ArgCUDAKernel(const int64_t height,     // n * h
                              const int64_t width,      // c
                              const int64_t post_size,  // h
                              const Reducer reducer, const T init, const T* in,
                              IndType* out) {
  typedef cub::BlockReduce<KeyValuePair<int, T>, BlockDim> BlockReduce;
  __shared__ typename BlockReduce::TempStorage temp_storage;

  for (int idx = blockIdx.x; idx < height; idx += gridDim.x) {
    KeyValuePair<int, T> kv_pair = {-1, init};
    int h = idx / post_size;
    int w = idx % post_size;
    for (int k = threadIdx.x; k < width; k += blockDim.x) {
      kv_pair =
          reducer({k, in[h * width * post_size + k * post_size + w]}, kv_pair);
    }
    kv_pair = BlockReduce(temp_storage).Reduce(kv_pair, reducer);
    if (threadIdx.x == 0) {
      out[idx] = static_cast<IndType>(kv_pair.key);
    }
    __syncthreads();
  }
}

template <typename T, typename IndType, class Reducer>
void ComputeFullArg(const platform::CUDADeviceContext& ctx, const Tensor& input,
                    Tensor* indices, const int64_t pre, const int64_t post,
                    const int64_t n) {
  auto cu_stream = ctx.stream();
  auto ComputeBlockSize = [](int64_t col) {
    if (col > 512)
      return 1024;
    else if (col > 256)
      return 512;
    else if (col > 128)
      return 256;
    else if (col > 64)
      return 128;
    else if (col > 32)
      return 64;
    else if (col > 16)
      return 32;
    else if (col > 8)
      return 16;
    else
      return 8;
  };

  int64_t max_grid_dimx = ctx.GetCUDAMaxGridDimSize().x;
  int64_t height = pre * post;
  int64_t width = n;
  int64_t grid_size = height < max_grid_dimx ? height : max_grid_dimx;

  const T* in_data = input.data<T>();
  IndType* out_data = indices->mutable_data<IndType>(ctx.GetPlace());

  if (typeid(Reducer) == typeid(cub::ArgMax)) {
    switch (ComputeBlockSize(width)) {
      FIXED_BLOCK_DIM_CASE(
          ArgCUDAKernel<T, IndType, Reducer,
                        kBlockDim><<<grid_size, kBlockDim, 0, cu_stream>>>(
              height, width, post, Reducer(), std::numeric_limits<T>::lowest(),
              in_data, out_data));
    }
  } else {
    switch (ComputeBlockSize(width)) {
      FIXED_BLOCK_DIM_CASE(
          ArgCUDAKernel<T, IndType, Reducer,
                        kBlockDim><<<grid_size, kBlockDim, 0, cu_stream>>>(
              height, width, post, Reducer(), std::numeric_limits<T>::max(),
              in_data, out_data));
    }
  }
}

template <typename T, class Reducer>
struct VisitDataCudaArgMinMaxFunctor {
  const framework::ExecutionContext& ctx;

  explicit VisitDataCudaArgMinMaxFunctor(const framework::ExecutionContext& ctx)
      : ctx(ctx) {}
  template <typename IndType>
  void apply() const {
    auto* input = ctx.Input<Tensor>("X");
    auto* output = ctx.Output<Tensor>("Out");
    int axis = ctx.Attr<int64_t>("axis");
    const bool& flatten = ctx.Attr<bool>("flatten");

    framework::DDim input_dims;
    if (flatten) {
      input_dims = framework::make_ddim({input->numel()});
      // if flatten, the axis just as 0
      axis = 0;
    } else {
      input_dims = input->dims();
      if (axis < 0) axis += input->dims().size();
    }

    int64_t numel = input->numel();
    int64_t groups = numel / input_dims[axis];
    int64_t pre = 1;
    int64_t post = 1;
    int64_t n = input_dims[axis];

    for (int i = 0; i < axis; i++) {
      pre *= input_dims[i];
    }

    for (int i = axis + 1; i < input_dims.size(); i++) {
      post *= input_dims[i];
    }

    const auto& dev_ctx = ctx.cuda_device_context();
    ComputeFullArg<T, IndType, Reducer>(dev_ctx, *input, output, pre, post, n);
  }
};
template <typename T, class Reducer>
class ArgMinMaxOpCUDAKernel : public framework::OpKernel<T> {
 public:
  void Compute(const framework::ExecutionContext& ctx) const override {
    auto& dtype = ctx.Attr<int>("dtype");
    if (dtype < 0) {
      framework::VisitDataType(static_cast<framework::proto::VarType::Type>(
                                   framework::proto::VarType::INT64),
                               VisitDataCudaArgMinMaxFunctor<T, Reducer>(ctx));
      return;
    }
    framework::VisitDataType(
        static_cast<framework::proto::VarType::Type>(dtype),
        VisitDataCudaArgMinMaxFunctor<T, Reducer>(ctx));
  }
};

#endif

}  // namespace operators
}  // namespace paddle
