// Copyright (c) 2022 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.

#include "paddle/phi/kernels/affine_grid_grad_kernel.h"
#include "paddle/phi/backends/cpu/cpu_context.h"
#include "paddle/phi/common/int_array.h"
#include "paddle/phi/core/kernel_registry.h"

namespace phi {

template <typename T>
struct Linspace<phi::CPUContext, T> {
  void operator()(T start,
                  T end,
                  int count,
                  bool align_corners,
                  DenseTensor* numbers,
                  const phi::CPUContext& dev_ctx) {
    numbers->Resize(phi::make_ddim({count}));
    T* number_data = dev_ctx.template Alloc<T>(numbers);
    T slice = (end - start) / (T)(count - 1);
    if (!align_corners) {
      slice = (end - start) / (T)count;
      start *= (T)(count - 1) / (T)count;
    }
    for (int i = 0; i < count; ++i) {
      number_data[i] = start + (T)i * slice;
    }
  }
};

template <typename T, typename Context>
void AffineGridGradKernel(const Context& dev_ctx,
                          const DenseTensor& output_grad,
                          const IntArray& outputShape,
                          bool align_corners,
                          DenseTensor* input_grad) {
  auto& theta_grad = input_grad;
  int n = output_grad.dims()[0];
  auto& size_attr = outputShape.GetData();
  int h = 0;
  int w = 0;
  h = size_attr[2];
  w = size_attr[3];
  theta_grad->Resize(phi::make_ddim({n, 2, 3}));
  dev_ctx.template Alloc<T>(theta_grad);
  phi::funcs::SetConstant<Context, T>()(dev_ctx, theta_grad, static_cast<T>(0));
  DenseTensor grid;
  GetIdxMap<Context, T>(n, h, w, align_corners, &grid, dev_ctx);
  // output = grid * theta.T
  // TODO(wanghaoshuang): Refine batched matrix multiply
  auto blas = phi::funcs::GetBlas<Context, T>(dev_ctx);
  for (int i = 0; i < n; ++i) {
    DenseTensor sliced_grid = grid.Slice(i, i + 1).Resize(
        {static_cast<int64_t>(h) * static_cast<int64_t>(w), 3});
    DenseTensor sliced_out_grad = output_grad.Slice(i, i + 1).Resize(
        {static_cast<int64_t>(h) * static_cast<int64_t>(w), 2});
    DenseTensor sliced_theta_grad = theta_grad->Slice(i, i + 1).Resize({2, 3});
    blas.MatMul(sliced_out_grad,
                true,
                sliced_grid,
                false,
                T(1),
                &sliced_theta_grad,
                T(0));
  }
}

}  // namespace phi

PD_REGISTER_KERNEL(affine_grid_grad,
                   CPU,
                   ALL_LAYOUT,
                   phi::AffineGridGradKernel,
                   float,
                   double){};