/* ----------------------------------------------------------------------
   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 "compute_pair.h"

#include "error.h"
#include "force.h"
#include "pair.h"
#include "update.h"

#include <cctype>
#include <cstring>

using namespace LAMMPS_NS;

enum { EPAIR, EVDWL, ECOUL };

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

ComputePair::ComputePair(LAMMPS *lmp, int narg, char **arg) :
    Compute(lmp, narg, arg), pstyle(nullptr), pair(nullptr), one(nullptr)
{
  if (narg < 4) utils::missing_cmd_args(FLERR, "compute pair", error);

  scalar_flag = 1;
  extscalar = 1;
  peflag = 1;
  timeflag = 1;

  // copy with suffix so we can later chop it off, if needed
  if (lmp->suffix)
    pstyle = utils::strdup(fmt::format("{}/{}", arg[3], lmp->suffix));
  else
    pstyle = utils::strdup(arg[3]);

  int iarg = 4;
  nsub = 0;
  evalue = EPAIR;

  if (narg > iarg) {
    if (isdigit(arg[iarg][0])) {
      nsub = utils::inumeric(FLERR, arg[iarg], false, lmp);
      ++iarg;
      if (nsub <= 0) error->all(FLERR, "Illegal compute pair command");
    }
  }

  if (narg > iarg) {
    if (strcmp(arg[iarg], "epair") == 0)
      evalue = EPAIR;
    else if (strcmp(arg[iarg], "evdwl") == 0)
      evalue = EVDWL;
    else if (strcmp(arg[iarg], "ecoul") == 0)
      evalue = ECOUL;
    else
      error->all(FLERR, "Unknown compute pair keyword {}", arg[iarg]);
    ++iarg;
  }

  // check if pair style with and without suffix exists

  pair = force->pair_match(pstyle, 1, nsub);
  if (!pair && lmp->suffix) {
    pstyle[strlen(pstyle) - strlen(lmp->suffix) - 1] = '\0';
    pair = force->pair_match(pstyle, 1, nsub);
  }

  if (!pair) error->all(FLERR, "Unused pair style {} in compute pair command", pstyle);
  npair = pair->nextra;

  if (npair) {
    vector_flag = 1;
    size_vector = npair;
    extvector = 1;
    one = new double[npair];
    vector = new double[npair];
  } else
    one = vector = nullptr;
}

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

ComputePair::~ComputePair()
{
  delete[] pstyle;
  delete[] one;
  delete[] vector;
}

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

void ComputePair::init()
{
  // recheck for pair style in case it has been deleted

  pair = force->pair_match(pstyle, 1, nsub);
  if (!pair) error->all(FLERR, "Unrecognized pair style {} in compute pair command", pstyle);
}

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

double ComputePair::compute_scalar()
{
  invoked_scalar = update->ntimestep;
  if (update->eflag_global != invoked_scalar)
    error->all(FLERR, "Energy was not tallied on needed timestep");

  double eng;
  if (evalue == EPAIR)
    eng = pair->eng_vdwl + pair->eng_coul;
  else if (evalue == EVDWL)
    eng = pair->eng_vdwl;
  else if (evalue == ECOUL)
    eng = pair->eng_coul;

  MPI_Allreduce(&eng, &scalar, 1, MPI_DOUBLE, MPI_SUM, world);
  return scalar;
}

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

void ComputePair::compute_vector()
{
  invoked_vector = update->ntimestep;
  if (update->eflag_global != invoked_vector)
    error->all(FLERR, "Energy was not tallied on needed timestep");

  for (int i = 0; i < npair; i++) one[i] = pair->pvector[i];
  MPI_Allreduce(one, vector, npair, MPI_DOUBLE, MPI_SUM, world);
}