/* ----------------------------------------------------------------------
   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: Paul Crozier (SNL)
------------------------------------------------------------------------- */

#include "pair_coul_long.h"

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

#include <cmath>
#include <cstring>

using namespace LAMMPS_NS;

#define EWALD_F 1.12837917
#define EWALD_P 0.3275911
#define A1 0.254829592
#define A2 -0.284496736
#define A3 1.421413741
#define A4 -1.453152027
#define A5 1.061405429

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

PairCoulLong::PairCoulLong(LAMMPS *lmp) : Pair(lmp)
{
  ewaldflag = pppmflag = 1;
  ftable = nullptr;
  qdist = 0.0;
  cut_respa = nullptr;
}

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

PairCoulLong::~PairCoulLong()
{
  if (copymode) return;

  if (allocated) {
    memory->destroy(setflag);
    memory->destroy(cutsq);

    memory->destroy(scale);
  }
  if (ftable) free_tables();
}

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

void PairCoulLong::compute(int eflag, int vflag)
{
  int i, j, ii, jj, inum, jnum, itable, itype, jtype;
  double qtmp, xtmp, ytmp, ztmp, delx, dely, delz, ecoul, fpair;
  double fraction, table;
  double r, r2inv, forcecoul, factor_coul;
  double grij, expm2, prefactor, t, erfc;
  int *ilist, *jlist, *numneigh, **firstneigh;
  double rsq;

  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];

      if (rsq < cut_coulsq) {
        r2inv = 1.0 / rsq;
        if (!ncoultablebits || rsq <= tabinnersq) {
          r = sqrt(rsq);
          grij = g_ewald * r;
          expm2 = exp(-grij * grij);
          t = 1.0 / (1.0 + EWALD_P * grij);
          erfc = t * (A1 + t * (A2 + t * (A3 + t * (A4 + t * A5)))) * expm2;
          prefactor = qqrd2e * scale[itype][jtype] * qtmp * q[j] / r;
          forcecoul = prefactor * (erfc + EWALD_F * grij * expm2);
          if (factor_coul < 1.0) forcecoul -= (1.0 - factor_coul) * prefactor;
        } else {
          union_int_float_t rsq_lookup;
          rsq_lookup.f = rsq;
          itable = rsq_lookup.i & ncoulmask;
          itable >>= ncoulshiftbits;
          fraction = (rsq_lookup.f - rtable[itable]) * drtable[itable];
          table = ftable[itable] + fraction * dftable[itable];
          forcecoul = scale[itype][jtype] * qtmp * q[j] * table;
          if (factor_coul < 1.0) {
            table = ctable[itable] + fraction * dctable[itable];
            prefactor = scale[itype][jtype] * qtmp * q[j] * table;
            forcecoul -= (1.0 - factor_coul) * prefactor;
          }
        }

        fpair = forcecoul * r2inv;

        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 (!ncoultablebits || rsq <= tabinnersq)
            ecoul = prefactor * erfc;
          else {
            table = etable[itable] + fraction * detable[itable];
            ecoul = scale[itype][jtype] * qtmp * q[j] * table;
          }
          if (factor_coul < 1.0) ecoul -= (1.0 - factor_coul) * prefactor;
        }

        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 PairCoulLong::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(scale, n + 1, n + 1, "pair:scale");
}

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

void PairCoulLong::settings(int narg, char **arg)
{
  if (narg != 1) error->all(FLERR, "Illegal pair_style command");

  cut_coul = utils::numeric(FLERR, arg[0], false, lmp);
}

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

void PairCoulLong::coeff(int narg, char **arg)
{
  if (narg != 2) 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);

  int count = 0;
  for (int i = ilo; i <= ihi; i++) {
    for (int j = MAX(jlo, i); j <= jhi; j++) {
      scale[i][j] = 1.0;
      setflag[i][j] = 1;
      count++;
    }
  }

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

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

void PairCoulLong::init_style()
{
  if (!atom->q_flag) error->all(FLERR, "Pair style lj/cut/coul/long requires atom attribute q");

  neighbor->request(this, instance_me);

  cut_coulsq = cut_coul * cut_coul;

  // insure use of KSpace long-range solver, set g_ewald

  if (force->kspace == nullptr) error->all(FLERR, "Pair style requires a KSpace style");
  g_ewald = force->kspace->g_ewald;

  // setup force tables

  if (ncoultablebits) init_tables(cut_coul, nullptr);
}

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

double PairCoulLong::init_one(int i, int j)
{
  scale[j][i] = scale[i][j];
  return cut_coul + 2.0 * qdist;
}

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

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

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

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

void PairCoulLong::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, &scale[i][j], sizeof(double), 1, fp, nullptr, error);
        MPI_Bcast(&scale[i][j], 1, MPI_DOUBLE, 0, world);
      }
    }
}

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

void PairCoulLong::write_restart_settings(FILE *fp)
{
  fwrite(&cut_coul, sizeof(double), 1, fp);
  fwrite(&offset_flag, sizeof(int), 1, fp);
  fwrite(&mix_flag, sizeof(int), 1, fp);
  fwrite(&ncoultablebits, sizeof(int), 1, fp);
  fwrite(&tabinner, sizeof(double), 1, fp);
}

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

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

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

double PairCoulLong::single(int i, int j, int /*itype*/, int /*jtype*/, double rsq,
                            double factor_coul, double /*factor_lj*/, double &fforce)
{
  double r2inv, r, grij, expm2, t, erfc, prefactor;
  double fraction, table, forcecoul, phicoul;
  int itable;

  r2inv = 1.0 / rsq;
  if (!ncoultablebits || rsq <= tabinnersq) {
    r = sqrt(rsq);
    grij = g_ewald * r;
    expm2 = exp(-grij * grij);
    t = 1.0 / (1.0 + EWALD_P * grij);
    erfc = t * (A1 + t * (A2 + t * (A3 + t * (A4 + t * A5)))) * expm2;
    prefactor = force->qqrd2e * atom->q[i] * atom->q[j] / r;
    forcecoul = prefactor * (erfc + EWALD_F * grij * expm2);
    if (factor_coul < 1.0) forcecoul -= (1.0 - factor_coul) * prefactor;
  } else {
    union_int_float_t rsq_lookup;
    rsq_lookup.f = rsq;
    itable = rsq_lookup.i & ncoulmask;
    itable >>= ncoulshiftbits;
    fraction = (rsq_lookup.f - rtable[itable]) * drtable[itable];
    table = ftable[itable] + fraction * dftable[itable];
    forcecoul = atom->q[i] * atom->q[j] * table;
    if (factor_coul < 1.0) {
      table = ctable[itable] + fraction * dctable[itable];
      prefactor = atom->q[i] * atom->q[j] * table;
      forcecoul -= (1.0 - factor_coul) * prefactor;
    }
  }
  fforce = forcecoul * r2inv;

  if (!ncoultablebits || rsq <= tabinnersq)
    phicoul = prefactor * erfc;
  else {
    table = etable[itable] + fraction * detable[itable];
    phicoul = atom->q[i] * atom->q[j] * table;
  }
  if (factor_coul < 1.0) phicoul -= (1.0 - factor_coul) * prefactor;

  return phicoul;
}

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

void *PairCoulLong::extract(const char *str, int &dim)
{
  if (strcmp(str, "cut_coul") == 0) {
    dim = 0;
    return (void *) &cut_coul;
  }
  if (strcmp(str, "scale") == 0) {
    dim = 2;
    return (void *) scale;
  }
  return nullptr;
}