/* This program illustrates use of parallel real FFT */
static char help[] = "This program illustrates the use of parallel real multi-dimensional fftw (without PETSc interface)";
#include <petscmat.h>
#include <fftw3.h>
#include <fftw3-mpi.h>

int main(int argc, char **args)
{
  ptrdiff_t     N0 = 2, N1 = 2, N2 = 2, N3 = 2, dim[4], N, D;
  fftw_plan     bplan, fplan;
  fftw_complex *out;
  double       *in1, *in2;
  ptrdiff_t     alloc_local, local_n0, local_0_start;
  ptrdiff_t     local_n1, local_1_start;
  PetscInt      i, j, indx[100], n1;
  PetscInt      size, rank, n, *in, N_factor;
  PetscScalar  *data_fin, value1, one = 1.0, zero = 0.0;
  PetscScalar   a, *x_arr, *y_arr, *z_arr, enorm;
  Vec           fin, fout, fout1, x, y;
  PetscRandom   rnd;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &args, NULL, help));
#if defined(PETSC_USE_COMPLEX)
  SETERRQ(PETSC_COMM_WORLD, PETSC_ERR_SUP, "This example requires real numbers. Your current scalar type is complex");
#endif
  PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
  PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));

  PetscRandomCreate(PETSC_COMM_WORLD, &rnd);
  D      = 4;
  dim[0] = N0;
  dim[1] = N1;
  dim[2] = N2;
  dim[3] = N3 / 2 + 1;

  alloc_local = fftw_mpi_local_size_transposed(D, dim, PETSC_COMM_WORLD, &local_n0, &local_0_start, &local_n1, &local_1_start);

  printf("The value alloc_local is %ld from process %d\n", alloc_local, rank);
  printf("The value local_n0 is %ld from process %d\n", local_n0, rank);
  printf("The value local_0_start is  %ld from process %d\n", local_0_start, rank);
  printf("The value local_n1 is  %ld from process %d\n", local_n1, rank);
  printf("The value local_1_start is  %ld from process %d\n", local_1_start, rank);

  /* Allocate space for input and output arrays  */

  in1 = (double *)fftw_malloc(sizeof(double) * alloc_local * 2);
  in2 = (double *)fftw_malloc(sizeof(double) * alloc_local * 2);
  out = (fftw_complex *)fftw_malloc(sizeof(fftw_complex) * alloc_local);

  N        = 2 * N0 * N1 * N2 * (N3 / 2 + 1);
  N_factor = N0 * N1 * N2 * N3;
  n        = 2 * local_n0 * N1 * N2 * (N3 / 2 + 1);
  n1       = local_n1 * N0 * 2 * N1 * N2;

  /*    printf("The value N is  %d from process %d\n",N,rank); */
  /*    printf("The value n is  %d from process %d\n",n,rank); */
  /*    printf("The value n1 is  %d from process %d\n",n1,rank); */
  /* Creating data vector and accompanying array with VeccreateMPIWithArray */
  PetscCall(VecCreateMPIWithArray(PETSC_COMM_WORLD, 1, n, N, (PetscScalar *)in1, &fin));
  PetscCall(VecCreateMPIWithArray(PETSC_COMM_WORLD, 1, n, N, (PetscScalar *)out, &fout));
  PetscCall(VecCreateMPIWithArray(PETSC_COMM_WORLD, 1, n, N, (PetscScalar *)in2, &fout1));

  /*    VecGetSize(fin,&size); */
  /*    printf("The size is %d\n",size); */

  VecSet(fin, one);
  /*    VecAssemblyBegin(fin); */
  /*    VecAssemblyEnd(fin); */
  /*    VecView(fin,PETSC_VIEWER_STDOUT_WORLD); */

  VecGetArray(fin, &x_arr);
  VecGetArray(fout1, &z_arr);
  VecGetArray(fout, &y_arr);

  dim[3] = N3;

  fplan = fftw_mpi_plan_dft_r2c(D, dim, (double *)x_arr, (fftw_complex *)y_arr, PETSC_COMM_WORLD, FFTW_ESTIMATE);
  bplan = fftw_mpi_plan_dft_c2r(D, dim, (fftw_complex *)y_arr, (double *)z_arr, PETSC_COMM_WORLD, FFTW_ESTIMATE);

  fftw_execute(fplan);
  fftw_execute(bplan);

  VecRestoreArray(fin, &x_arr);
  VecRestoreArray(fout1, &z_arr);
  VecRestoreArray(fout, &y_arr);

  /*    a = 1.0/(PetscReal)N_factor; */
  /*    PetscCall(VecScale(fout1,a)); */

  VecAssemblyBegin(fout1);
  VecAssemblyEnd(fout1);

  VecView(fout1, PETSC_VIEWER_STDOUT_WORLD);

  fftw_destroy_plan(fplan);
  fftw_destroy_plan(bplan);
  fftw_free(in1);
  PetscCall(VecDestroy(&fin));
  fftw_free(out);
  PetscCall(VecDestroy(&fout));
  fftw_free(in2);
  PetscCall(VecDestroy(&fout1));

  PetscCall(PetscFinalize());
  return 0;
}