/* ----------------------------------------------------------------------
   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
   https://www.lammps.org/, Sandia National Laboratories
   Steve Plimpton, sjplimp@sandia.gov

   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.
------------------------------------------------------------------------- */
/* ----------------------------------------------------------------------
   Contributing author: Wengen Ouyang (Tel Aviv University)
   e-mail: w.g.ouyang at gmail dot com

   This is a Coulomb potential described in
   [Maaravi et al, J. Phys. Chem. C 121, 22826-22835 (2017)]
------------------------------------------------------------------------- */

#include "pair_coul_shield.h"

#include "atom.h"
#include "comm.h"
#include "error.h"
#include "force.h"
#include "interlayer_taper.h"
#include "math_special.h"
#include "memory.h"
#include "neigh_list.h"
#include "neighbor.h"

#include <cmath>

using namespace LAMMPS_NS;
using namespace InterLayer;

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

PairCoulShield::PairCoulShield(LAMMPS *lmp) : Pair(lmp)
{
  tap_flag = 1;
}

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

PairCoulShield::~PairCoulShield()
{
  if (allocated) {
    memory->destroy(setflag);
    memory->destroy(sigmae);
    memory->destroy(offset);
    memory->destroy(cutsq);
    memory->destroy(cut);
    allocated = 0;
  }
}

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

void PairCoulShield::compute(int eflag, int vflag)
{
  int i, j, ii, jj, inum, jnum, itype, jtype;
  double qtmp, xtmp, ytmp, ztmp, delx, dely, delz, ecoul, fpair, Tap, dTap;
  double rsq, r, r3, rarg, th, depsdr, epsr, forcecoul, factor_coul, Vc, fvc;
  int *ilist, *jlist, *numneigh, **firstneigh;

  ecoul = 0.0;
  ev_init(eflag, vflag);

  double **x = atom->x;
  double **f = atom->f;
  double *q = atom->q;
  int *type = atom->type;
  int nlocal = atom->nlocal;
  double *special_coul = force->special_coul;
  int newton_pair = force->newton_pair;
  double qqrd2e = force->qqrd2e;

  inum = list->inum;
  ilist = list->ilist;
  numneigh = list->numneigh;
  firstneigh = list->firstneigh;

  // loop over neighbors of my atoms

  for (ii = 0; ii < inum; ii++) {
    i = ilist[ii];
    qtmp = q[i];
    xtmp = x[i][0];
    ytmp = x[i][1];
    ztmp = x[i][2];
    itype = type[i];
    jlist = firstneigh[i];
    jnum = numneigh[i];

    for (jj = 0; jj < jnum; jj++) {
      j = jlist[jj];

      factor_coul = special_coul[sbmask(j)];
      j &= NEIGHMASK;

      delx = xtmp - x[j][0];
      dely = ytmp - x[j][1];
      delz = ztmp - x[j][2];
      rsq = delx * delx + dely * dely + delz * delz;
      jtype = type[j];

      // only include the interaction between different layers
      if (rsq < cutsq[itype][jtype] && atom->molecule[i] != atom->molecule[j]) {
        r = sqrt(rsq);
        r3 = rsq * r;
        rarg = 1.0 / sigmae[itype][jtype];
        th = r3 + MathSpecial::cube(rarg);
        epsr = 1.0 / pow(th, 1.0 / 3.0);
        depsdr = MathSpecial::square(epsr);
        depsdr *= depsdr;
        Vc = qqrd2e * qtmp * q[j] * epsr;

        // turn on/off taper function
        if (tap_flag) {
          Tap = calc_Tap(r, cut[itype][jtype]);
          dTap = calc_dTap(r, cut[itype][jtype]);
        } else {
          Tap = 1.0;
          dTap = 0.0;
        }

        forcecoul = qqrd2e * qtmp * q[j] * r * depsdr;
        fvc = forcecoul * Tap - Vc * dTap / r;
        fpair = factor_coul * fvc;

        f[i][0] += delx * fpair;
        f[i][1] += dely * fpair;
        f[i][2] += delz * fpair;
        if (newton_pair || j < nlocal) {
          f[j][0] -= delx * fpair;
          f[j][1] -= dely * fpair;
          f[j][2] -= delz * fpair;
        }

        if (eflag) {
          if (tap_flag)
            ecoul = Vc * Tap;
          else
            ecoul = Vc - offset[itype][jtype];
          ecoul *= factor_coul;
        }

        if (evflag) ev_tally(i, j, nlocal, newton_pair, 0.0, ecoul, fpair, delx, dely, delz);
      }
    }
  }

  if (vflag_fdotr) virial_fdotr_compute();
}

/* ----------------------------------------------------------------------
   allocate all arrays
------------------------------------------------------------------------- */

void PairCoulShield::allocate()
{
  allocated = 1;
  int n = atom->ntypes;

  memory->create(setflag, n + 1, n + 1, "pair:setflag");
  for (int i = 1; i <= n; i++)
    for (int j = i; j <= n; j++) setflag[i][j] = 0;

  memory->create(cutsq, n + 1, n + 1, "pair:cutsq");
  memory->create(cut, n + 1, n + 1, "pair:cut");
  memory->create(sigmae, n + 1, n + 1, "pair:sigmae");
  memory->create(offset, n + 1, n + 1, "pair:offset");
}

/* ----------------------------------------------------------------------
   global settings
------------------------------------------------------------------------- */

void PairCoulShield::settings(int narg, char **arg)
{
  if (narg < 1 || narg > 2) error->all(FLERR, "Illegal pair_style command");

  cut_global = utils::numeric(FLERR, arg[0], false, lmp);
  if (narg == 2) tap_flag = utils::numeric(FLERR, arg[1], false, lmp);

  // reset cutoffs that have been explicitly set

  if (allocated) {
    int i, j;
    for (i = 1; i <= atom->ntypes; i++)
      for (j = i + 1; j <= atom->ntypes; j++)
        if (setflag[i][j]) cut[i][j] = cut_global;
  }
}

/* ----------------------------------------------------------------------
   set coeffs for one or more type pairs
------------------------------------------------------------------------- */

void PairCoulShield::coeff(int narg, char **arg)
{
  if (narg < 3 || narg > 4) error->all(FLERR, "Incorrect args for pair coefficients");
  if (!allocated) allocate();

  int ilo, ihi, jlo, jhi;
  utils::bounds(FLERR, arg[0], 1, atom->ntypes, ilo, ihi, error);
  utils::bounds(FLERR, arg[1], 1, atom->ntypes, jlo, jhi, error);

  double sigmae_one = utils::numeric(FLERR, arg[2], false, lmp);

  double cut_one = cut_global;
  if (narg == 4) cut_one = utils::numeric(FLERR, arg[3], false, lmp);

  int count = 0;
  for (int i = ilo; i <= ihi; i++) {
    for (int j = MAX(jlo, i); j <= jhi; j++) {
      sigmae[i][j] = sigmae_one;
      cut[i][j] = cut_one;
      setflag[i][j] = 1;
      count++;
    }
  }

  if (count == 0) error->all(FLERR, "Incorrect args for pair coefficients");
}

/* ----------------------------------------------------------------------
   init specific to this pair style
------------------------------------------------------------------------- */

void PairCoulShield::init_style()
{
  if (!atom->q_flag) error->all(FLERR, "Pair style coul/shield requires atom attribute q");
  if (!atom->molecule_flag)
    error->all(FLERR, "Pair style coul/shield requires atom attribute molecule");

  neighbor->request(this, instance_me);
}

/* ----------------------------------------------------------------------
   init for one type pair i,j and corresponding j,i
------------------------------------------------------------------------- */

double PairCoulShield::init_one(int i, int j)
{
  if (setflag[i][j] == 0) {
    error->all(FLERR,
               "for pair style coul/shield, parameters need to be set explicitly for all pairs.");
  }

  double *q = atom->q;
  double qqrd2e = force->qqrd2e;
  double r, r3, rarg, th, epsr;

  if (offset_flag) {
    r = cut[i][j];
    r3 = r * r * r;
    rarg = 1.0 / sigmae[i][j];
    th = r3 + MathSpecial::cube(rarg);
    epsr = 1.0 / pow(th, 1.0 / 3.0);
    offset[i][j] = qqrd2e * q[i] * q[j] * epsr;
  } else
    offset[i][j] = 0.0;

  sigmae[j][i] = sigmae[i][j];
  offset[j][i] = offset[i][j];
  cut[j][i] = cut[i][j];

  return cut[i][j];
}

/* ----------------------------------------------------------------------
  proc 0 writes to restart file
------------------------------------------------------------------------- */

void PairCoulShield::write_restart(FILE *fp)
{
  write_restart_settings(fp);

  int i, j;
  for (i = 1; i <= atom->ntypes; i++)
    for (j = i; j <= atom->ntypes; j++) {
      fwrite(&setflag[i][j], sizeof(int), 1, fp);
      if (setflag[i][j]) {
        fwrite(&sigmae[i][j], sizeof(double), 1, fp);
        fwrite(&cut[i][j], sizeof(double), 1, fp);
      }
    }
}

/* ----------------------------------------------------------------------
  proc 0 reads from restart file, bcasts
------------------------------------------------------------------------- */

void PairCoulShield::read_restart(FILE *fp)
{
  read_restart_settings(fp);
  allocate();

  int i, j;
  int me = comm->me;
  for (i = 1; i <= atom->ntypes; i++)
    for (j = i; j <= atom->ntypes; j++) {
      if (me == 0) utils::sfread(FLERR, &setflag[i][j], sizeof(int), 1, fp, nullptr, error);
      MPI_Bcast(&setflag[i][j], 1, MPI_INT, 0, world);
      if (setflag[i][j]) {
        if (me == 0) {
          utils::sfread(FLERR, &sigmae[i][j], sizeof(double), 1, fp, nullptr, error);
          utils::sfread(FLERR, &cut[i][j], sizeof(double), 1, fp, nullptr, error);
        }
        MPI_Bcast(&sigmae[i][j], 1, MPI_DOUBLE, 0, world);
        MPI_Bcast(&cut[i][j], 1, MPI_DOUBLE, 0, world);
      }
    }
}

/* ----------------------------------------------------------------------
  proc 0 writes to restart file
------------------------------------------------------------------------- */

void PairCoulShield::write_restart_settings(FILE *fp)
{
  fwrite(&cut_global, sizeof(double), 1, fp);
  fwrite(&offset_flag, sizeof(int), 1, fp);
  fwrite(&mix_flag, sizeof(int), 1, fp);
}

/* ----------------------------------------------------------------------
  proc 0 reads from restart file, bcasts
------------------------------------------------------------------------- */

void PairCoulShield::read_restart_settings(FILE *fp)
{
  if (comm->me == 0) {
    utils::sfread(FLERR, &cut_global, sizeof(double), 1, fp, nullptr, error);
    utils::sfread(FLERR, &offset_flag, sizeof(int), 1, fp, nullptr, error);
    utils::sfread(FLERR, &mix_flag, sizeof(int), 1, fp, nullptr, error);
  }
  MPI_Bcast(&cut_global, 1, MPI_DOUBLE, 0, world);
  MPI_Bcast(&offset_flag, 1, MPI_INT, 0, world);
  MPI_Bcast(&mix_flag, 1, MPI_INT, 0, world);
}

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

double PairCoulShield::single(int i, int j, int itype, int jtype, double rsq, double factor_coul,
                              double /*factor_lj*/, double &fforce)
{
  double r, rarg, Vc, fvc, forcecoul, phishieldec;
  double r3, th, epsr, depsdr, Tap, dTap;
  double *q = atom->q;
  double qqrd2e = force->qqrd2e;

  // only computed between different layers as indicated by different molecule ids.

  if (atom->molecule[i] == atom->molecule[j]) {
    fforce = 0.0;
    return 0.0;
  }

  r = sqrt(rsq);
  r3 = rsq * r;
  rarg = 1.0 / sigmae[itype][jtype];
  th = r3 + MathSpecial::cube(rarg);
  epsr = 1.0 / pow(th, 1.0 / 3.0);
  depsdr = epsr * epsr;
  depsdr *= depsdr;
  Vc = qqrd2e * q[i] * q[j] * epsr;

  // turn on/off taper function
  if (tap_flag) {
    Tap = calc_Tap(r, cut[itype][jtype]);
    dTap = calc_dTap(r, cut[itype][jtype]);
  } else {
    Tap = 1.0;
    dTap = 0.0;
  }

  forcecoul = qqrd2e * q[i] * q[j] * r * depsdr;
  fvc = forcecoul * Tap - Vc * dTap / r;
  fforce = factor_coul * fvc;

  if (tap_flag)
    phishieldec = Vc * Tap;
  else
    phishieldec = Vc - offset[itype][jtype];
  return factor_coul * phishieldec;
}
