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

   This software is distributed under the GNU General Public License.

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

/* ----------------------------------------------------------------------
   Contributing author: Axel Kohlmeyer (Temple U)
------------------------------------------------------------------------- */

#include "pair_beck_omp.h"

#include "atom.h"
#include "comm.h"
#include "force.h"
#include "math_special.h"
#include "neigh_list.h"
#include "suffix.h"

#include <cmath>

#include "omp_compat.h"
using namespace LAMMPS_NS;
using namespace MathSpecial;

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

PairBeckOMP::PairBeckOMP(LAMMPS *lmp) : PairBeck(lmp), ThrOMP(lmp, THR_PAIR)
{
  suffix_flag |= Suffix::OMP;
  respa_enable = 0;
}

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

void PairBeckOMP::compute(int eflag, int vflag)
{
  ev_init(eflag, vflag);

  const int nall = atom->nlocal + atom->nghost;
  const int nthreads = comm->nthreads;
  const int inum = list->inum;

#if defined(_OPENMP)
#pragma omp parallel LMP_DEFAULT_NONE LMP_SHARED(eflag, vflag)
#endif
  {
    int ifrom, ito, tid;

    loop_setup_thr(ifrom, ito, tid, inum, nthreads);
    ThrData *thr = fix->get_thr(tid);
    thr->timer(Timer::START);
    ev_setup_thr(eflag, vflag, nall, eatom, vatom, nullptr, thr);

    if (evflag) {
      if (eflag) {
        if (force->newton_pair)
          eval<1, 1, 1>(ifrom, ito, thr);
        else
          eval<1, 1, 0>(ifrom, ito, thr);
      } else {
        if (force->newton_pair)
          eval<1, 0, 1>(ifrom, ito, thr);
        else
          eval<1, 0, 0>(ifrom, ito, thr);
      }
    } else {
      if (force->newton_pair)
        eval<0, 0, 1>(ifrom, ito, thr);
      else
        eval<0, 0, 0>(ifrom, ito, thr);
    }

    thr->timer(Timer::PAIR);
    reduce_thr(this, eflag, vflag, thr);
  }    // end of omp parallel region
}

template <int EVFLAG, int EFLAG, int NEWTON_PAIR>
void PairBeckOMP::eval(int iifrom, int iito, ThrData *const thr)
{
  int i, j, ii, jj, jnum, itype, jtype;
  double xtmp, ytmp, ztmp, delx, dely, delz, evdwl, fpair;
  double rsq, r5, force_beck, factor_lj;
  double r, rinv;
  double aaij, alphaij, betaij;
  double term1, term1inv, term2, term3, term4, term5, term6;
  int *ilist, *jlist, *numneigh, **firstneigh;

  evdwl = 0.0;

  const auto *_noalias const x = (dbl3_t *) atom->x[0];
  auto *_noalias const f = (dbl3_t *) thr->get_f()[0];
  int *type = atom->type;
  int nlocal = atom->nlocal;
  double *special_lj = force->special_lj;
  double fxtmp, fytmp, fztmp;

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

  // loop over neighbors of my atoms

  for (ii = iifrom; ii < iito; ++ii) {

    i = ilist[ii];
    xtmp = x[i].x;
    ytmp = x[i].y;
    ztmp = x[i].z;
    itype = type[i];
    jlist = firstneigh[i];
    jnum = numneigh[i];
    fxtmp = fytmp = fztmp = 0.0;

    for (jj = 0; jj < jnum; jj++) {
      j = jlist[jj];
      factor_lj = special_lj[sbmask(j)];
      j &= NEIGHMASK;

      delx = xtmp - x[j].x;
      dely = ytmp - x[j].y;
      delz = ztmp - x[j].z;
      rsq = delx * delx + dely * dely + delz * delz;
      jtype = type[j];

      if (rsq < cutsq[itype][jtype]) {
        r = sqrt(rsq);
        r5 = rsq * rsq * r;
        aaij = aa[itype][jtype];
        alphaij = alpha[itype][jtype];
        betaij = beta[itype][jtype];
        term1 = aaij * aaij + rsq;
        term2 = powint(term1, -5);
        term3 = 21.672 + 30.0 * aaij * aaij + 6.0 * rsq;
        term4 = alphaij + r5 * betaij;
        term5 = alphaij + 6.0 * r5 * betaij;
        rinv = 1.0 / r;
        force_beck = AA[itype][jtype] * exp(-1.0 * r * term4) * term5;
        force_beck -= BB[itype][jtype] * r * term2 * term3;

        fpair = factor_lj * force_beck * rinv;

        f[i].x += delx * fpair;
        f[i].y += dely * fpair;
        f[i].z += delz * fpair;
        if (NEWTON_PAIR || j < nlocal) {
          f[j].x -= delx * fpair;
          f[j].y -= dely * fpair;
          f[j].z -= delz * fpair;
        }

        if (EFLAG) {
          term6 = powint(term1, -3);
          term1inv = 1.0 / term1;
          evdwl = AA[itype][jtype] * exp(-1.0 * r * term4);
          evdwl -= BB[itype][jtype] * term6 * (1.0 + (2.709 + 3.0 * aaij * aaij) * term1inv);
          evdwl *= factor_lj;
        }

        if (EVFLAG)
          ev_tally_thr(this, i, j, nlocal, NEWTON_PAIR, evdwl, 0.0, fpair, delx, dely, delz, thr);
      }
    }
    f[i].x += fxtmp;
    f[i].y += fytmp;
    f[i].z += fztmp;
  }
}

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

double PairBeckOMP::memory_usage()
{
  double bytes = memory_usage_thr();
  bytes += PairBeck::memory_usage();

  return bytes;
}