static char help[] = "DMSwarm-PIC demonstrator of advecting points within cell DM defined by a DA or PLEX object \n\
Options: \n\
-ppcell   : Number of times to sub-divide the reference cell when layout the initial particle coordinates \n\
-meshtype : 0 ==> DA , 1 ==> PLEX \n\
-nt       : Number of timestep to perform \n\
-view     : Write out initial condition and time dependent data \n";

#include <petsc.h>
#include <petscdm.h>
#include <petscdmda.h>
#include <petscdmswarm.h>

PetscErrorCode pic_advect(PetscInt ppcell, PetscInt meshtype)
{
  const PetscInt dim = 2;
  DM             celldm, swarm;
  PetscInt       tk, nt = 200;
  PetscBool      view = PETSC_FALSE;
  Vec            pfields[1];
  PetscReal      minradius;
  PetscReal      dt;
  PetscReal      vel[]        = {1.0, 0.16};
  const char    *fieldnames[] = {"phi"};
  PetscViewer    viewer;

  PetscFunctionBegin;
  PetscCall(PetscOptionsGetBool(NULL, NULL, "-view", &view, NULL));
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-nt", &nt, NULL));

  /* Create the background cell DM */
  if (meshtype == 0) { /* DA */
    PetscInt nxy;
    PetscInt dof           = 1;
    PetscInt stencil_width = 1;

    PetscCall(PetscPrintf(PETSC_COMM_WORLD, "Mesh type: DMDA\n"));
    nxy = 33;
    PetscCall(DMDACreate2d(PETSC_COMM_WORLD, DM_BOUNDARY_NONE, DM_BOUNDARY_NONE, DMDA_STENCIL_BOX, nxy, nxy, PETSC_DECIDE, PETSC_DECIDE, dof, stencil_width, NULL, NULL, &celldm));

    PetscCall(DMDASetElementType(celldm, DMDA_ELEMENT_Q1));

    PetscCall(DMSetFromOptions(celldm));

    PetscCall(DMSetUp(celldm));

    PetscCall(DMDASetUniformCoordinates(celldm, 0.0, 1.0, 0.0, 1.0, 0.0, 1.5));

    minradius = 1.0 / ((PetscReal)(nxy - 1));

    PetscCall(PetscPrintf(PETSC_COMM_WORLD, "DA(minradius) %1.4e\n", (double)minradius));
  }

  if (meshtype == 1) { /* PLEX */
    DM           distributedMesh = NULL;
    PetscInt     numComp[]       = {1};
    PetscInt     numDof[]        = {1, 0, 0}; /* vert, edge, cell */
    PetscInt     faces[]         = {1, 1, 1};
    PetscInt     numBC           = 0;
    PetscSection section;
    Vec          cellgeom = NULL;
    Vec          facegeom = NULL;

    PetscCall(PetscPrintf(PETSC_COMM_WORLD, "Mesh type: DMPLEX\n"));
    PetscCall(DMPlexCreateBoxMesh(PETSC_COMM_WORLD, dim, PETSC_TRUE, faces, NULL, NULL, PETSC_TRUE, &celldm));

    /* Distribute mesh over processes */
    PetscCall(DMPlexDistribute(celldm, 0, NULL, &distributedMesh));
    if (distributedMesh) {
      PetscCall(DMDestroy(&celldm));
      celldm = distributedMesh;
    }

    PetscCall(DMSetFromOptions(celldm));

    PetscCall(DMPlexCreateSection(celldm, NULL, numComp, numDof, numBC, NULL, NULL, NULL, NULL, &section));
    PetscCall(DMSetLocalSection(celldm, section));

    PetscCall(DMSetUp(celldm));

    /* Calling DMPlexComputeGeometryFVM() generates the value returned by DMPlexGetMinRadius() */
    PetscCall(DMPlexComputeGeometryFVM(celldm, &cellgeom, &facegeom));
    PetscCall(DMPlexGetMinRadius(celldm, &minradius));
    PetscCall(PetscPrintf(PETSC_COMM_WORLD, "PLEX(minradius) %1.4e\n", (double)minradius));
    PetscCall(VecDestroy(&cellgeom));
    PetscCall(VecDestroy(&facegeom));
    PetscCall(PetscSectionDestroy(&section));
  }

  /* Create the DMSwarm */
  PetscCall(DMCreate(PETSC_COMM_WORLD, &swarm));
  PetscCall(DMSetType(swarm, DMSWARM));
  PetscCall(DMSetDimension(swarm, dim));

  /* Configure swarm to be of type PIC */
  PetscCall(DMSwarmSetType(swarm, DMSWARM_PIC));
  PetscCall(DMSwarmSetCellDM(swarm, celldm));

  /* Register two scalar fields within the DMSwarm */
  PetscCall(DMSwarmRegisterPetscDatatypeField(swarm, "phi", 1, PETSC_REAL));
  PetscCall(DMSwarmRegisterPetscDatatypeField(swarm, "region", 1, PETSC_REAL));
  PetscCall(DMSwarmFinalizeFieldRegister(swarm));

  /* Set initial local sizes of the DMSwarm with a buffer length of zero */
  PetscCall(DMSwarmSetLocalSizes(swarm, 4, 0));

  /* Insert swarm coordinates cell-wise */
  /*PetscCall(DMSwarmInsertPointsUsingCellDM(swarm,DMSWARMPIC_LAYOUT_REGULAR,ppcell));*/
  PetscCall(DMSwarmInsertPointsUsingCellDM(swarm, DMSWARMPIC_LAYOUT_SUBDIVISION, ppcell));

  /* Define initial conditions for th swarm fields "phi" and "region" */
  {
    PetscReal *s_coor, *s_phi, *s_region;
    PetscInt   npoints, p;

    PetscCall(DMSwarmGetLocalSize(swarm, &npoints));
    PetscCall(DMSwarmGetField(swarm, DMSwarmPICField_coor, NULL, NULL, (void **)&s_coor));
    PetscCall(DMSwarmGetField(swarm, "phi", NULL, NULL, (void **)&s_phi));
    PetscCall(DMSwarmGetField(swarm, "region", NULL, NULL, (void **)&s_region));
    for (p = 0; p < npoints; p++) {
      PetscReal pos[2];
      pos[0] = s_coor[2 * p + 0];
      pos[1] = s_coor[2 * p + 1];

      s_region[p] = 1.0;
      s_phi[p]    = 1.0 + PetscExpReal(-200.0 * ((pos[0] - 0.5) * (pos[0] - 0.5) + (pos[1] - 0.5) * (pos[1] - 0.5)));
    }
    PetscCall(DMSwarmRestoreField(swarm, "region", NULL, NULL, (void **)&s_region));
    PetscCall(DMSwarmRestoreField(swarm, "phi", NULL, NULL, (void **)&s_phi));
    PetscCall(DMSwarmRestoreField(swarm, DMSwarmPICField_coor, NULL, NULL, (void **)&s_coor));
  }

  /* Project initial value of phi onto the mesh */
  PetscCall(DMCreateGlobalVector(celldm, &pfields[0]));
  PetscCall(DMSwarmProjectFields(swarm, NULL, 1, fieldnames, pfields, SCATTER_FORWARD));

  if (view) {
    /* View swarm all swarm fields using data type PETSC_REAL */
    PetscCall(DMSwarmViewXDMF(swarm, "ic_dms.xmf"));

    /* View projected swarm field "phi" */
    PetscCall(PetscViewerCreate(PETSC_COMM_WORLD, &viewer));
    PetscCall(PetscViewerSetType(viewer, PETSCVIEWERVTK));
    PetscCall(PetscViewerFileSetMode(viewer, FILE_MODE_WRITE));
    if (meshtype == 0) { /* DA */
      PetscCall(PetscViewerFileSetName(viewer, "ic_dmda.vts"));
      PetscCall(VecView(pfields[0], viewer));
    }
    if (meshtype == 1) { /* PLEX */
      PetscCall(PetscViewerFileSetName(viewer, "ic_dmplex.vtk"));
      PetscCall(DMView(celldm, viewer));
      PetscCall(VecView(pfields[0], viewer));
    }
    PetscCall(PetscViewerDestroy(&viewer));
  }

  PetscCall(DMView(celldm, PETSC_VIEWER_STDOUT_WORLD));
  PetscCall(DMView(swarm, PETSC_VIEWER_STDOUT_WORLD));

  dt = 0.5 * minradius / PetscSqrtReal(vel[0] * vel[0] + vel[1] * vel[1]);
  for (tk = 1; tk <= nt; tk++) {
    PetscReal *s_coor;
    PetscInt   npoints, p;

    PetscCall(PetscPrintf(PETSC_COMM_WORLD, "[step %" PetscInt_FMT "]\n", tk));
    /* advect with analytic prescribed (constant) velocity field */
    PetscCall(DMSwarmGetLocalSize(swarm, &npoints));
    PetscCall(DMSwarmGetField(swarm, DMSwarmPICField_coor, NULL, NULL, (void **)&s_coor));
    for (p = 0; p < npoints; p++) {
      s_coor[2 * p + 0] += dt * vel[0];
      s_coor[2 * p + 1] += dt * vel[1];
    }
    PetscCall(DMSwarmRestoreField(swarm, DMSwarmPICField_coor, NULL, NULL, (void **)&s_coor));

    PetscCall(DMSwarmMigrate(swarm, PETSC_TRUE));

    /* Ad-hoc cell filling algorithm */
    /*
       The injection frequency is chosen for default DA case.
       They will likely not be appropriate for the general case using an unstructure PLEX mesh.
    */
    if (tk % 10 == 0) {
      PetscReal dx              = 1.0 / 32.0;
      PetscInt  npoints_dir_x[] = {32, 1};
      PetscReal min[2], max[2];

      min[0] = 0.5 * dx;
      max[0] = 0.5 * dx + 31.0 * dx;
      min[1] = 0.5 * dx;
      max[1] = 0.5 * dx;
      PetscCall(DMSwarmSetPointsUniformCoordinates(swarm, min, max, npoints_dir_x, ADD_VALUES));
    }
    if (tk % 2 == 0) {
      PetscReal dx              = 1.0 / 32.0;
      PetscInt  npoints_dir_y[] = {2, 31};
      PetscReal min[2], max[2];

      min[0] = 0.05 * dx;
      max[0] = 0.5 * dx;
      min[1] = 0.5 * dx;
      max[1] = 0.5 * dx + 31.0 * dx;
      PetscCall(DMSwarmSetPointsUniformCoordinates(swarm, min, max, npoints_dir_y, ADD_VALUES));
    }

    /* Project swarm field "phi" onto the cell DM */
    PetscCall(DMSwarmProjectFields(swarm, NULL, 1, fieldnames, pfields, SCATTER_FORWARD));

    if (view) {
      PetscViewer viewer;
      char        fname[PETSC_MAX_PATH_LEN];

      /* View swarm fields */
      PetscCall(PetscSNPrintf(fname, PETSC_MAX_PATH_LEN - 1, "step%.4" PetscInt_FMT "_dms.xmf", tk));
      PetscCall(DMSwarmViewXDMF(swarm, fname));

      /* View projected field */
      PetscCall(PetscViewerCreate(PETSC_COMM_WORLD, &viewer));
      PetscCall(PetscViewerSetType(viewer, PETSCVIEWERVTK));
      PetscCall(PetscViewerFileSetMode(viewer, FILE_MODE_WRITE));

      if (meshtype == 0) { /* DA */
        PetscCall(PetscSNPrintf(fname, PETSC_MAX_PATH_LEN - 1, "step%.4" PetscInt_FMT "_dmda.vts", tk));
        PetscCall(PetscViewerFileSetName(viewer, fname));
        PetscCall(VecView(pfields[0], viewer));
      }
      if (meshtype == 1) { /* PLEX */
        PetscCall(PetscSNPrintf(fname, PETSC_MAX_PATH_LEN - 1, "step%.4" PetscInt_FMT "_dmplex.vtk", tk));
        PetscCall(PetscViewerFileSetName(viewer, fname));
        PetscCall(DMView(celldm, viewer));
        PetscCall(VecView(pfields[0], viewer));
      }
      PetscCall(PetscViewerDestroy(&viewer));
    }
  }
  PetscCall(VecDestroy(&pfields[0]));
  PetscCall(DMDestroy(&celldm));
  PetscCall(DMDestroy(&swarm));

  PetscFunctionReturn(PETSC_SUCCESS);
}

int main(int argc, char **args)
{
  PetscInt ppcell   = 1;
  PetscInt meshtype = 0;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &args, (char *)0, help));
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-ppcell", &ppcell, NULL));
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-meshtype", &meshtype, NULL));
  PetscCheck(meshtype <= 1, PETSC_COMM_WORLD, PETSC_ERR_USER, "-meshtype <value> must be 0 or 1");

  PetscCall(pic_advect(ppcell, meshtype));

  PetscCall(PetscFinalize());
  return 0;
}