// Copyright (c) 2024 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/svdvals_kernel.h"
#include "paddle/phi/backends/cpu/cpu_context.h"
#include "paddle/phi/core/kernel_registry.h"
#include "paddle/phi/kernels/funcs/complex_functors.h"
#include "paddle/phi/kernels/funcs/lapack/lapack_function.h"
#include "paddle/phi/kernels/transpose_kernel.h"

namespace phi {

template <typename T>
void LapackSvdvals(const T* X, T* S, int rows, int cols) {
  // Using N to neglect computing U、VH
  char jobz = 'N';
  T* a = const_cast<T*>(X);
  int lda = rows;
  int lwork = -1;
  std::vector<T> work(1);
  int info = 0;
  // Get the best lwork
  funcs::lapackSvd<T, dtype::Real<T>>(jobz,
                                      rows,
                                      cols,
                                      a,
                                      lda,
                                      S,
                                      nullptr,  // U is not needed
                                      1,        // dummy dimension for U
                                      nullptr,  // VH is not needed
                                      1,        // dummy dimension for VH
                                      work.data(),
                                      lwork,
                                      nullptr,  // rwork is not needed
                                      nullptr,  // iwork is not needed
                                      &info);
  if (info != 0) {
    PADDLE_THROW(common::errors::InvalidArgument(
        "Error during LAPACK lwork query. Invalid matrix or arguments."));
  }
  lwork = static_cast<int>(work[0]);
  work.resize(lwork);
  funcs::lapackSvd<T, dtype::Real<T>>(jobz,
                                      rows,
                                      cols,
                                      a,
                                      lda,
                                      S,
                                      nullptr,  // U is not needed
                                      1,        // dummy dimension for U
                                      nullptr,  // VH is not needed
                                      1,        // dummy dimension for VH
                                      work.data(),
                                      lwork,
                                      nullptr,  // rwork is not needed
                                      nullptr,  // iwork is not needed
                                      &info);
  if (info < 0) {
    PADDLE_THROW(common::errors::InvalidArgument(
        "This %s-th argument has an illegal value.", info));
  }
  if (info > 0) {
    PADDLE_THROW(common::errors::InvalidArgument(
        "SVD computation did not converge. Input matrix may be invalid."));
  }
}

template <typename T>
void BatchSvdvals(
    const T* X, T* S, int64_t rows, int64_t cols, int64_t batches) {
  int64_t stride = rows * cols;
  int64_t stride_s = std::min(rows, cols);
  for (int64_t i = 0; i < batches; i++) {
    LapackSvdvals<T>(X + i * stride, S + i * stride_s, rows, cols);
  }
}

template <typename T, typename Context>
void SvdvalsKernel(const Context& dev_ctx,
                   const DenseTensor& X,
                   DenseTensor* S) {
  if (S && S->numel() == 0) {
    dev_ctx.template Alloc<dtype::Real<T>>(S);
    return;
  }
  auto x_dims = X.dims();
  int64_t rows = static_cast<int64_t>(x_dims[x_dims.size() - 2]);
  int64_t cols = static_cast<int64_t>(x_dims[x_dims.size() - 1]);
  PADDLE_ENFORCE_LT(rows * cols,
                    std::numeric_limits<int32_t>::max(),
                    common::errors::InvalidArgument(
                        "The product of rows and columns must be less than %d.",
                        std::numeric_limits<int32_t>::max()));

  // Validate dimensions
  PADDLE_ENFORCE_GT(
      rows,
      0,
      common::errors::InvalidArgument("The row of Input(X) must be > 0."));
  PADDLE_ENFORCE_GT(
      cols,
      0,
      common::errors::InvalidArgument("The column of Input(X) must be > 0."));
  int64_t k = std::min(rows, cols);
  int64_t batches = static_cast<int64_t>(X.numel() / (rows * cols));
  PADDLE_ENFORCE_GT(batches,
                    0,
                    common::errors::InvalidArgument(
                        "The batch size of Input(X) must be > 0."));
  DDim s_dims;
  if (x_dims.size() <= 2) {
    s_dims = {k};
  } else {
    s_dims = {batches, k};
  }
  S->Resize(s_dims);
  // Allocate memory for output
  auto* S_out = dev_ctx.template Alloc<dtype::Real<T>>(S);

  // Transpose the last two dimensions for LAPACK compatibility
  DenseTensor trans_x = TransposeLast2Dim<T>(dev_ctx, X);
  auto* x_data = trans_x.data<T>();
  // Perform batch SVD computation for singular values
  BatchSvdvals<T>(x_data, S_out, rows, cols, batches);
}

}  // namespace phi

// Register the kernel for CPU
PD_REGISTER_KERNEL(
    svdvals, CPU, ALL_LAYOUT, phi::SvdvalsKernel, float, double) {}