static char help[] = "Tests MATHTOOL with a derived htool::IMatrix<PetscScalar> class\n\n";

#include <petscmat.h>
#include <htool/hmatrix/interfaces/virtual_generator.hpp>

static PetscErrorCode GenEntries(PetscInt sdim, PetscInt M, PetscInt N, const PetscInt *J, const PetscInt *K, PetscScalar *ptr, void *ctx)
{
  PetscInt  d, j, k;
  PetscReal diff = 0.0, *coords = (PetscReal *)(ctx);

  PetscFunctionBeginUser;
  for (j = 0; j < M; j++) {
    for (k = 0; k < N; k++) {
      diff = 0.0;
      for (d = 0; d < sdim; d++) diff += (coords[J[j] * sdim + d] - coords[K[k] * sdim + d]) * (coords[J[j] * sdim + d] - coords[K[k] * sdim + d]);
      ptr[j + M * k] = 1.0 / (1.0e-2 + PetscSqrtReal(diff));
    }
  }
  PetscFunctionReturn(PETSC_SUCCESS);
}
class MyIMatrix : public htool::VirtualGenerator<PetscScalar> {
private:
  PetscReal *coords;
  PetscInt   sdim;

public:
  MyIMatrix(PetscInt spacedim, PetscReal *gcoords) : htool::VirtualGenerator<PetscScalar>(), coords(gcoords), sdim(spacedim) { }

  virtual void copy_submatrix(PetscInt M, PetscInt N, const PetscInt *J, const PetscInt *K, PetscScalar *ptr) const override
  {
    PetscReal diff = 0.0;

    PetscFunctionBeginUser;
    for (PetscInt j = 0; j < M; j++) /* could be optimized by the user how they see fit, e.g., vectorization */
      for (PetscInt k = 0; k < N; k++) {
        diff = 0.0;
        for (PetscInt d = 0; d < sdim; d++) diff += (coords[J[j] * sdim + d] - coords[K[k] * sdim + d]) * (coords[J[j] * sdim + d] - coords[K[k] * sdim + d]);
        ptr[j + M * k] = 1.0 / (1.0e-2 + PetscSqrtReal(diff));
      }
    PetscFunctionReturnVoid();
  }
};

int main(int argc, char **argv)
{
  Mat               A, B, P, R;
  PetscInt          m = 100, dim = 3, M, begin = 0;
  PetscMPIInt       size;
  PetscReal        *coords, *gcoords, norm, epsilon, relative;
  PetscBool         flg, sym = PETSC_FALSE;
  PetscRandom       rdm;
  MatHtoolKernelFn *kernel = GenEntries;
  MyIMatrix        *imatrix;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &argv, NULL, help));
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-m_local", &m, NULL));
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-dim", &dim, NULL));
  PetscCall(PetscOptionsGetBool(NULL, NULL, "-symmetric", &sym, NULL));
  PetscCall(PetscOptionsGetReal(NULL, NULL, "-mat_htool_epsilon", &epsilon, NULL));
  PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
  M = size * m;
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-M", &M, NULL));
  PetscCall(PetscMalloc1(m * dim, &coords));
  PetscCall(PetscRandomCreate(PETSC_COMM_WORLD, &rdm));
  PetscCall(PetscRandomGetValuesReal(rdm, m * dim, coords));
  PetscCall(PetscCalloc1(M * dim, &gcoords));
  PetscCallMPI(MPI_Exscan(&m, &begin, 1, MPIU_INT, MPI_SUM, PETSC_COMM_WORLD));
  PetscCall(PetscArraycpy(gcoords + begin * dim, coords, m * dim));
  PetscCallMPI(MPIU_Allreduce(MPI_IN_PLACE, gcoords, M * dim, MPIU_REAL, MPI_SUM, PETSC_COMM_WORLD));
  imatrix = new MyIMatrix(dim, gcoords);
  PetscCall(MatCreateHtoolFromKernel(PETSC_COMM_WORLD, m, m, M, M, dim, coords, coords, NULL, imatrix, &A)); /* block-wise assembly using htool::IMatrix<PetscScalar>::copy_submatrix() */
  PetscCall(MatSetOption(A, MAT_SYMMETRIC, sym));
  PetscCall(MatSetFromOptions(A));
  PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
  PetscCall(MatViewFromOptions(A, NULL, "-A_view"));
  PetscCall(MatCreateHtoolFromKernel(PETSC_COMM_WORLD, m, m, M, M, dim, coords, coords, kernel, gcoords, &B)); /* entry-wise assembly using GenEntries() */
  PetscCall(MatSetOption(B, MAT_SYMMETRIC, sym));
  PetscCall(MatSetFromOptions(B));
  PetscCall(MatAssemblyBegin(B, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(B, MAT_FINAL_ASSEMBLY));
  PetscCall(MatViewFromOptions(B, NULL, "-B_view"));
  PetscCall(MatMultEqual(A, B, 10, &flg));
  PetscCheck(flg, PETSC_COMM_WORLD, PETSC_ERR_PLIB, "Ax != Bx");
  PetscCall(MatConvert(A, MATDENSE, MAT_INITIAL_MATRIX, &P));
  PetscCall(MatNorm(P, NORM_FROBENIUS, &relative));
  PetscCall(MatConvert(B, MATDENSE, MAT_INITIAL_MATRIX, &R));
  PetscCall(MatAXPY(R, -1.0, P, SAME_NONZERO_PATTERN));
  PetscCall(MatNorm(R, NORM_INFINITY, &norm));
  PetscCheck(PetscAbsReal(norm / relative) <= epsilon, PETSC_COMM_WORLD, PETSC_ERR_PLIB, "||A(!symmetric)-A(symmetric)|| = %g (> %g)", (double)PetscAbsReal(norm / relative), (double)epsilon);
  PetscCall(MatDestroy(&B));
  PetscCall(MatDestroy(&R));
  PetscCall(MatDestroy(&P));
  PetscCall(PetscRandomDestroy(&rdm));
  PetscCall(MatDestroy(&A));
  PetscCall(PetscFree(gcoords));
  PetscCall(PetscFree(coords));
  delete imatrix;
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   build:
      requires: htool
   testset:
      requires: htool
      output_file: output/empty.out
      nsize: 4
      args: -m_local 120 -mat_htool_epsilon 1.0e-2
      test:
        args: -symmetric
      test:
        args: -mat_htool_block_tree_consistency false

TEST*/