static char help[] = "Landau collision operator driver\n\n";

#include <petscts.h>
#include <petsclandau.h>

typedef struct {
  PetscInt  grid_target, batch_target, field_target;
  PetscBool init;
} ex1Ctx;

/*
 call back method for DMPlexLandauAccess:

Input Parameters:
 .   dm - a DM for this field
 -   local_field - the local index in the grid for this field
 .   grid - the grid index
 +   b_id - the batch index
 -   vctx - a user context

 Input/Output Parameters:
 +   x - Vector to data to

 */
PetscErrorCode landau_field_print_access_callback(DM dm, Vec x, PetscInt local_field, PetscInt grid, PetscInt b_id, void *vctx)
{
  ex1Ctx    *user = (ex1Ctx *)vctx;
  LandauCtx *ctx;

  PetscFunctionBegin;
  PetscCall(DMGetApplicationContext(dm, &ctx));
  if (grid == user->grid_target && b_id == user->batch_target && local_field == user->field_target) {
    PetscScalar one = 1.0e10;

    PetscCall(VecSet(x, one));
    if (!user->init) {
      PetscCall(PetscObjectSetName((PetscObject)dm, "single"));
      PetscCall(DMViewFromOptions(dm, NULL, "-ex1_dm_view")); // DMCreateSubDM does seem to give the DM's fild the name from the original DM
      user->init = PETSC_TRUE;
    }
    PetscCall(PetscObjectSetName((PetscObject)x, "u"));      // this gives the vector a nicer name, DMCreateSubDM could do this for us and get the correct name
    PetscCall(VecViewFromOptions(x, NULL, "-ex1_vec_view")); // this causes diffs with Kokkos, etc
    PetscCall(PetscInfo(dm, "DMPlexLandauAccess user 'add' method to grid %" PetscInt_FMT ", batch %" PetscInt_FMT " and species %" PetscInt_FMT "\n", grid, b_id, ctx->species_offset[grid] + local_field));
  }
  PetscFunctionReturn(0);
}

int main(int argc, char **argv)
{
  DM             pack;
  Vec            X, X_0;
  PetscInt       dim = 2;
  TS             ts;
  Mat            J;
  SNES           snes;
  KSP            ksp;
  PC             pc;
  SNESLineSearch linesearch;
  PetscReal      time;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &argv, NULL, help));
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-dim", &dim, NULL));
  /* Create a mesh */
  PetscCall(DMPlexLandauCreateVelocitySpace(PETSC_COMM_SELF, dim, "", &X, &J, &pack));
  PetscCall(DMSetUp(pack));
  PetscCall(VecDuplicate(X, &X_0));
  PetscCall(VecCopy(X, X_0));
  PetscCall(DMPlexLandauPrintNorms(X, 0));
  PetscCall(DMSetOutputSequenceNumber(pack, 0, 0.0));
  /* Create timestepping solver context */
  PetscCall(TSCreate(PETSC_COMM_SELF, &ts));
  PetscCall(TSSetDM(ts, pack));
  PetscCall(TSGetSNES(ts, &snes));
  PetscCall(SNESGetLineSearch(snes, &linesearch));
  PetscCall(SNESLineSearchSetType(linesearch, SNESLINESEARCHBASIC));
  PetscCall(TSSetIFunction(ts, NULL, DMPlexLandauIFunction, NULL));
  PetscCall(TSSetIJacobian(ts, J, J, DMPlexLandauIJacobian, NULL));
  PetscCall(TSSetExactFinalTime(ts, TS_EXACTFINALTIME_STEPOVER));
  PetscCall(SNESGetKSP(snes, &ksp));
  PetscCall(KSPGetPC(ksp, &pc));
  PetscCall(TSSetFromOptions(ts));
  PetscCall(TSSetSolution(ts, X));
  PetscCall(TSSolve(ts, X));
  PetscCall(DMPlexLandauPrintNorms(X, 1));
  PetscCall(TSGetTime(ts, &time));
  PetscCall(DMSetOutputSequenceNumber(pack, 1, time));
  PetscCall(VecAXPY(X, -1, X_0));
  { /* test add field method */
    ex1Ctx    *user;
    LandauCtx *ctx;
    PetscCall(DMGetApplicationContext(pack, &ctx));
    PetscCall(PetscNew(&user));
    user->grid_target  = 1; // 2nd ion species
    user->field_target = 1;
    PetscCall(DMPlexLandauAccess(pack, X, landau_field_print_access_callback, user));
    PetscCall(PetscFree(user));
  }
  /* clean up */
  PetscCall(DMPlexLandauDestroyVelocitySpace(&pack));
  PetscCall(TSDestroy(&ts));
  PetscCall(VecDestroy(&X));
  PetscCall(VecDestroy(&X_0));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST
  testset:
    requires: p4est !complex double defined(PETSC_USE_DMLANDAU_2D)
    output_file: output/ex1_0.out
    filter: grep -v "%  type: seq"
    args: -dm_landau_num_species_grid 1,2 -petscspace_degree 3 -petscspace_poly_tensor 1 -dm_landau_type p4est -dm_landau_ion_masses 2,4 -dm_landau_ion_charges 1,18 -dm_landau_thermal_temps 5,5,.5 -dm_landau_n 1.00018,1,1e-5 -dm_landau_n_0 1e20 -ts_monitor -snes_rtol 1.e-14 -snes_stol 1.e-14 -snes_monitor -snes_converged_reason -ts_type arkimex -ts_arkimex_type 1bee -ts_max_snes_failures -1 -ts_rtol 1e-1 -ts_dt 1.e-1 -ts_max_time 1 -ts_adapt_clip .5,1.25 -ts_adapt_scale_solve_failed 0.75 -ts_adapt_time_step_increase_delay 5 -ts_max_steps 1 -pc_type lu -ksp_type preonly -dm_landau_amr_levels_max 2,1 -ex1_dm_view  -ex1_vec_view ::ascii_matlab
    test:
      suffix: cpu
      args: -dm_landau_device_type cpu
    test:
      suffix: kokkos
      requires: kokkos_kernels
      args: -dm_landau_device_type kokkos -dm_mat_type aijkokkos -dm_vec_type kokkos
    test:
      suffix: cuda
      requires: cuda
      args: -dm_landau_device_type cuda -dm_mat_type aijcusparse -dm_vec_type cuda -mat_cusparse_use_cpu_solve

TEST*/