/* ----------------------------------------------------------------------
   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
   https://www.lammps.org/, Sandia National Laboratories
   LAMMPS development team: developers@lammps.org

   Copyright (2003) Sandia Corporation.  Under the terms of Contract
   DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
   certain rights in this software.  This software is distributed under
   the GNU General Public License.

   See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */

#include "fix_aveforce.h"

#include "atom.h"
#include "domain.h"
#include "error.h"
#include "input.h"
#include "modify.h"
#include "region.h"
#include "respa.h"
#include "update.h"
#include "variable.h"

#include <cstring>

using namespace LAMMPS_NS;
using namespace FixConst;

enum { NONE, CONSTANT, EQUAL };

/* ---------------------------------------------------------------------- */

FixAveForce::FixAveForce(LAMMPS *lmp, int narg, char **arg) :
    Fix(lmp, narg, arg), xstr(nullptr), ystr(nullptr), zstr(nullptr), idregion(nullptr),
    region(nullptr)
{
  if (narg < 6) error->all(FLERR, "Illegal fix aveforce command");

  dynamic_group_allow = 1;
  vector_flag = 1;
  size_vector = 3;
  global_freq = 1;
  extvector = 1;
  respa_level_support = 1;
  ilevel_respa = nlevels_respa = 0;

  xstr = ystr = zstr = nullptr;

  if (utils::strmatch(arg[3], "^v_")) {
    xstr = utils::strdup(arg[3] + 2);
  } else if (strcmp(arg[3], "NULL") == 0) {
    xstyle = NONE;
  } else {
    xvalue = utils::numeric(FLERR, arg[3], false, lmp);
    xstyle = CONSTANT;
  }
  if (utils::strmatch(arg[4], "^v_")) {
    ystr = utils::strdup(arg[4] + 2);
  } else if (strcmp(arg[4], "NULL") == 0) {
    ystyle = NONE;
  } else {
    yvalue = utils::numeric(FLERR, arg[4], false, lmp);
    ystyle = CONSTANT;
  }
  if (utils::strmatch(arg[5], "^v_")) {
    zstr = utils::strdup(arg[5] + 2);
  } else if (strcmp(arg[5], "NULL") == 0) {
    zstyle = NONE;
  } else {
    zvalue = utils::numeric(FLERR, arg[5], false, lmp);
    zstyle = CONSTANT;
  }

  // optional args

  int iarg = 6;
  while (iarg < narg) {
    if (strcmp(arg[iarg], "region") == 0) {
      if (iarg + 2 > narg) error->all(FLERR, "Illegal fix aveforce command");
      region = domain->get_region_by_id(arg[iarg + 1]);
      if (!region) error->all(FLERR, "Region {} for fix aveforce does not exist", arg[iarg + 1]);
      idregion = utils::strdup(arg[iarg + 1]);
      iarg += 2;
    } else
      error->all(FLERR, "Illegal fix aveforce command");
  }

  foriginal_all[0] = foriginal_all[1] = foriginal_all[2] = foriginal_all[3] = 0.0;
}

/* ---------------------------------------------------------------------- */

FixAveForce::~FixAveForce()
{
  delete[] xstr;
  delete[] ystr;
  delete[] zstr;
  delete[] idregion;
}

/* ---------------------------------------------------------------------- */

int FixAveForce::setmask()
{
  int mask = 0;
  mask |= POST_FORCE;
  mask |= POST_FORCE_RESPA;
  mask |= MIN_POST_FORCE;
  return mask;
}

/* ---------------------------------------------------------------------- */

void FixAveForce::init()
{
  // check variables

  if (xstr) {
    xvar = input->variable->find(xstr);
    if (xvar < 0) error->all(FLERR, "Variable name for fix aveforce does not exist");
    if (input->variable->equalstyle(xvar))
      xstyle = EQUAL;
    else
      error->all(FLERR, "Variable for fix aveforce is invalid style");
  }
  if (ystr) {
    yvar = input->variable->find(ystr);
    if (yvar < 0) error->all(FLERR, "Variable name for fix aveforce does not exist");
    if (input->variable->equalstyle(yvar))
      ystyle = EQUAL;
    else
      error->all(FLERR, "Variable for fix aveforce is invalid style");
  }
  if (zstr) {
    zvar = input->variable->find(zstr);
    if (zvar < 0) error->all(FLERR, "Variable name for fix aveforce does not exist");
    if (input->variable->equalstyle(zvar))
      zstyle = EQUAL;
    else
      error->all(FLERR, "Variable for fix aveforce is invalid style");
  }

  // set index and check validity of region

  if (idregion) {
    region = domain->get_region_by_id(idregion);
    if (!region) error->all(FLERR, "Region {} for fix aveforce does not exist", idregion);
  }

  if (xstyle == EQUAL || ystyle == EQUAL || zstyle == EQUAL)
    varflag = EQUAL;
  else
    varflag = CONSTANT;

  if (utils::strmatch(update->integrate_style, "^respa")) {
    nlevels_respa = (dynamic_cast<Respa *>(update->integrate))->nlevels;
    if (respa_level >= 0)
      ilevel_respa = MIN(respa_level, nlevels_respa - 1);
    else
      ilevel_respa = nlevels_respa - 1;
  }
}

/* ---------------------------------------------------------------------- */

void FixAveForce::setup(int vflag)
{
  if (utils::strmatch(update->integrate_style, "^verlet"))
    post_force(vflag);
  else
    for (int ilevel = 0; ilevel < nlevels_respa; ilevel++) {
      (dynamic_cast<Respa *>(update->integrate))->copy_flevel_f(ilevel);
      post_force_respa(vflag, ilevel, 0);
      (dynamic_cast<Respa *>(update->integrate))->copy_f_flevel(ilevel);
    }
}

/* ---------------------------------------------------------------------- */

void FixAveForce::min_setup(int vflag)
{
  post_force(vflag);
}

/* ---------------------------------------------------------------------- */

void FixAveForce::post_force(int /*vflag*/)
{
  // update region if necessary

  if (region) region->prematch();

  // sum forces on participating atoms

  double **x = atom->x;
  double **f = atom->f;
  int *mask = atom->mask;
  int nlocal = atom->nlocal;

  double foriginal[4];
  foriginal[0] = foriginal[1] = foriginal[2] = foriginal[3] = 0.0;

  for (int i = 0; i < nlocal; i++)
    if (mask[i] & groupbit) {
      if (region && !region->match(x[i][0], x[i][1], x[i][2])) continue;
      foriginal[0] += f[i][0];
      foriginal[1] += f[i][1];
      foriginal[2] += f[i][2];
      foriginal[3] += 1.0;
    }

  // average the force on participating atoms
  // add in requested amount, computed via variable evaluation if necessary
  // wrap variable evaluation with clear/add

  MPI_Allreduce(foriginal, foriginal_all, 4, MPI_DOUBLE, MPI_SUM, world);

  int ncount = static_cast<int>(foriginal_all[3]);
  if (ncount == 0) return;

  if (varflag == EQUAL) {
    modify->clearstep_compute();
    if (xstyle == EQUAL) xvalue = input->variable->compute_equal(xvar);
    if (ystyle == EQUAL) yvalue = input->variable->compute_equal(yvar);
    if (zstyle == EQUAL) zvalue = input->variable->compute_equal(zvar);
    modify->addstep_compute(update->ntimestep + 1);
  }

  double fave[3];
  fave[0] = foriginal_all[0] / ncount + xvalue;
  fave[1] = foriginal_all[1] / ncount + yvalue;
  fave[2] = foriginal_all[2] / ncount + zvalue;

  // set force of all participating atoms to same value
  // only for active dimensions

  for (int i = 0; i < nlocal; i++)
    if (mask[i] & groupbit) {
      if (region && !region->match(x[i][0], x[i][1], x[i][2])) continue;
      if (xstyle) f[i][0] = fave[0];
      if (ystyle) f[i][1] = fave[1];
      if (zstyle) f[i][2] = fave[2];
    }
}

/* ---------------------------------------------------------------------- */

void FixAveForce::post_force_respa(int vflag, int ilevel, int /*iloop*/)
{
  // ave + extra force on selected RESPA level
  // just ave on all other levels

  if (ilevel == ilevel_respa) {
    post_force(vflag);
  } else {
    if (region) region->prematch();

    double **x = atom->x;
    double **f = atom->f;
    int *mask = atom->mask;
    int nlocal = atom->nlocal;

    double foriginal[4];
    foriginal[0] = foriginal[1] = foriginal[2] = foriginal[3] = 0.0;

    for (int i = 0; i < nlocal; i++)
      if (mask[i] & groupbit) {
        if (region && !region->match(x[i][0], x[i][1], x[i][2])) continue;
        foriginal[0] += f[i][0];
        foriginal[1] += f[i][1];
        foriginal[2] += f[i][2];
        foriginal[3] += 1.0;
      }

    MPI_Allreduce(foriginal, foriginal_all, 4, MPI_DOUBLE, MPI_SUM, world);

    int ncount = static_cast<int>(foriginal_all[3]);
    if (ncount == 0) return;

    double fave[3];
    fave[0] = foriginal_all[0] / ncount;
    fave[1] = foriginal_all[1] / ncount;
    fave[2] = foriginal_all[2] / ncount;

    for (int i = 0; i < nlocal; i++)
      if (mask[i] & groupbit) {
        if (region && !region->match(x[i][0], x[i][1], x[i][2])) continue;
        if (xstyle) f[i][0] = fave[0];
        if (ystyle) f[i][1] = fave[1];
        if (zstyle) f[i][2] = fave[2];
      }
  }
}

/* ---------------------------------------------------------------------- */

void FixAveForce::min_post_force(int vflag)
{
  post_force(vflag);
}

/* ----------------------------------------------------------------------
   return components of total force on fix group before force was changed
------------------------------------------------------------------------- */

double FixAveForce::compute_vector(int n)
{
  return foriginal_all[n];
}