/* ----------------------------------------------------------------------
   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.
------------------------------------------------------------------------- */

/* ----------------------------------------------------------------------
   Contributing author: Christina Payne (Vanderbilt U)
                        Stan Moore (Sandia) for dipole terms
------------------------------------------------------------------------- */

#include "fix_efield.h"

#include "atom.h"
#include "comm.h"
#include "domain.h"
#include "error.h"
#include "force.h"
#include "input.h"
#include "memory.h"
#include "modify.h"
#include "pair.h"
#include "region.h"
#include "respa.h"
#include "update.h"
#include "variable.h"

#include <cstring>

using namespace LAMMPS_NS;
using namespace FixConst;

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

FixEfield::FixEfield(LAMMPS *lmp, int narg, char **arg) :
    Fix(lmp, narg, arg), xstr(nullptr), ystr(nullptr), zstr(nullptr), estr(nullptr),
    pstr(nullptr), idregion(nullptr), region(nullptr), efield(nullptr)
{
  if (narg < 6) utils::missing_cmd_args(FLERR, std::string("fix ") + style, error);

  dynamic_group_allow = 1;
  vector_flag = 1;
  scalar_flag = 1;
  size_vector = 3;
  global_freq = 1;
  extvector = 1;
  extscalar = 1;
  respa_level_support = 1;
  ilevel_respa = 0;
  energy_global_flag = 1;
  virial_global_flag = virial_peratom_flag = 1;

  qe2f = force->qe2f;
  xstyle = ystyle = zstyle = estyle = pstyle = NONE;

  if (utils::strmatch(arg[3], "^v_")) {
    xstr = utils::strdup(arg[3] + 2);
  } else {
    ex = qe2f * utils::numeric(FLERR, arg[3], false, lmp);
    xstyle = CONSTANT;
  }

  if (utils::strmatch(arg[4], "^v_")) {
    ystr = utils::strdup(arg[4] + 2);
  } else {
    ey = qe2f * utils::numeric(FLERR, arg[4], false, lmp);
    ystyle = CONSTANT;
  }

  if (utils::strmatch(arg[5], "^v_")) {
    zstr = utils::strdup(arg[5] + 2);
  } else {
    ez = qe2f * 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)
        utils::missing_cmd_args(FLERR, std::string("fix ") + style + " region", error);
      region = domain->get_region_by_id(arg[iarg + 1]);
      if (!region) error->all(FLERR, "Region {} for fix efield does not exist", arg[iarg + 1]);
      idregion = utils::strdup(arg[iarg + 1]);
      iarg += 2;
    } else if (strcmp(arg[iarg], "energy") == 0) {
      if (iarg + 2 > narg)
        utils::missing_cmd_args(FLERR, std::string("fix ") + style + "energy", error);
      if (utils::strmatch(arg[iarg + 1], "^v_")) {
        estr = utils::strdup(arg[iarg + 1] + 2);
      } else
        error->all(FLERR, "Unsupported argument for fix {} energy command: {}", style, arg[iarg]);
      iarg += 2;
    } else if (strcmp(arg[iarg], "potential") == 0) {
      if (iarg + 2 > narg)
        utils::missing_cmd_args(FLERR, std::string("fix ") + style + "potential", error);
      if (utils::strmatch(arg[iarg + 1], "^v_")) {
        pstr = utils::strdup(arg[iarg + 1] + 2);
      } else
        error->all(FLERR, "Unsupported argument for fix {} energy command: {}", style, arg[iarg]);
      iarg += 2;
    } else {
      error->all(FLERR, "Unknown keyword for fix {} command: {}", style, arg[iarg]);
    }
  }

  if (estr && pstr)
    error->all(FLERR, "Must not use energy and potential keywords at the same time with fix efield");

  force_flag = 0;
  fsum[0] = fsum[1] = fsum[2] = fsum[3] = 0.0;

  maxatom = atom->nmax;
  memory->create(efield, maxatom, 4, "efield:efield");

  maxatom_energy = 0;
}

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

FixEfield::~FixEfield()
{
  delete[] xstr;
  delete[] ystr;
  delete[] zstr;
  delete[] estr;
  delete[] pstr;
  delete[] idregion;
  memory->destroy(efield);
}

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

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

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

void FixEfield::init()
{
  qflag = muflag = 0;
  if (atom->q_flag) qflag = 1;
  if (atom->mu_flag && atom->torque_flag) muflag = 1;
  if (!qflag && !muflag) error->all(FLERR, "Fix {} requires atom attribute q or mu", style);

  // warn if TIP4P pair style is used with plain fix efield
  if ((strcmp(style, "efield") == 0) && (comm->me == 0)) {
    int itmp;
    if (force->pair && force->pair->extract("qdist", itmp))
      error->warning(FLERR, "Fix efield produces incorrect forces when applied to TIP4P atoms");
  }

  // check variables

  if (xstr) {
    xvar = input->variable->find(xstr);
    if (xvar < 0) error->all(FLERR, "Variable {} for x-field in fix {} does not exist", xstr, style);
    if (input->variable->equalstyle(xvar))
      xstyle = EQUAL;
    else if (input->variable->atomstyle(xvar))
      xstyle = ATOM;
    else
      error->all(FLERR, "Variable {} for x-field in fix {} is invalid style", xstr, style);
  }

  if (ystr) {
    yvar = input->variable->find(ystr);
    if (yvar < 0) error->all(FLERR, "Variable {} for y-field in fix {} does not exist", ystr, style);
    if (input->variable->equalstyle(yvar))
      ystyle = EQUAL;
    else if (input->variable->atomstyle(yvar))
      ystyle = ATOM;
    else
      error->all(FLERR, "Variable {} for y-field in fix {} is invalid style", ystr, style);
  }

  if (zstr) {
    zvar = input->variable->find(zstr);
    if (zvar < 0) error->all(FLERR, "Variable {} for z-field in fix {} does not exist", zstr, style);
    if (input->variable->equalstyle(zvar))
      zstyle = EQUAL;
    else if (input->variable->atomstyle(zvar))
      zstyle = ATOM;
    else
      error->all(FLERR, "Variable {} for z-field in fix {} is invalid style", zstr, style);
  }

  if (estr) {
    evar = input->variable->find(estr);
    if (evar < 0) error->all(FLERR, "Variable {} for energy in fix {} does not exist", estr, style);
    if (input->variable->atomstyle(evar))
      estyle = ATOM;
    else
      error->all(FLERR, "Variable {} for energy in fix {} must be atom-style", estr, style);
  }

  if (pstr) {
    pvar = input->variable->find(pstr);
    if (pvar < 0) error->all(FLERR, "Variable {} for potential in fix {} does not exist", pstr, style);
    if (input->variable->atomstyle(pvar))
      pstyle = ATOM;
    else
      error->all(FLERR, "Variable {} for potential in fix {} must be atom-style", pstr, 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 {} does not exist", idregion, style);
  }

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

  if (muflag && varflag == ATOM)
    error->all(FLERR, "Fix {} with dipoles cannot use atom-style variables", style);

  if (muflag && update->whichflag == 2 && comm->me == 0)
    error->warning(FLERR, "The minimizer does not re-orient dipoles when using fix {}", style);

  if (varflag == CONSTANT && estyle != NONE)
    error->all(FLERR, "Cannot use variable energy with constant efield in fix {}", style);
  if (varflag == CONSTANT && pstyle != NONE)
    error->all(FLERR, "Cannot use variable potential with constant efield in fix {}", style);
  if ((varflag == EQUAL || varflag == ATOM) && update->whichflag == 2 && estyle == NONE && pstyle == NONE)
    error->all(FLERR, "Must use variable energy or potential with fix {} during minimization", style);

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

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

void FixEfield::setup(int vflag)
{
  if (utils::strmatch(update->integrate_style, "^respa")) {
    auto respa = dynamic_cast<Respa *>(update->integrate);
    respa->copy_flevel_f(ilevel_respa);
    post_force_respa(vflag, ilevel_respa, 0);
    respa->copy_f_flevel(ilevel_respa);
  } else {
    post_force(vflag);
  }
}

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

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

/* ----------------------------------------------------------------------
   apply F = qE
------------------------------------------------------------------------- */

void FixEfield::post_force(int vflag)
{
  double **f = atom->f;
  double *q = atom->q;
  int *mask = atom->mask;
  imageint *image = atom->image;
  int nlocal = atom->nlocal;

  // virial setup

  v_init(vflag);

  // reallocate efield array if necessary

  if ((varflag == ATOM) && (atom->nmax > maxatom)) {
    maxatom = atom->nmax;
    memory->destroy(efield);
    memory->create(efield, maxatom, 4, "efield:efield");
  }

  // update region if necessary

  if (region) region->prematch();

  // fsum[0] = "potential energy" for added force
  // fsum[123] = extra force added to atoms

  fsum[0] = fsum[1] = fsum[2] = fsum[3] = 0.0;
  force_flag = 0;

  double **x = atom->x;
  double fx, fy, fz;
  double v[6], unwrap[3];
  ;

  // constant efield

  if (varflag == CONSTANT) {

    // charge interactions
    // force = qE, potential energy = F dot x in unwrapped coords

    if (qflag) {
      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;
          fx = q[i] * ex;
          fy = q[i] * ey;
          fz = q[i] * ez;
          f[i][0] += fx;
          f[i][1] += fy;
          f[i][2] += fz;

          domain->unmap(x[i], image[i], unwrap);
          fsum[0] -= fx * unwrap[0] + fy * unwrap[1] + fz * unwrap[2];
          fsum[1] += fx;
          fsum[2] += fy;
          fsum[3] += fz;
          if (evflag) {
            v[0] = fx * unwrap[0];
            v[1] = fy * unwrap[1];
            v[2] = fz * unwrap[2];
            v[3] = fx * unwrap[1];
            v[4] = fx * unwrap[2];
            v[5] = fy * unwrap[2];
            v_tally(i, v);
          }
        }
    }

    // dipole interactions
    // no force, torque = mu cross E, potential energy = -mu dot E

    if (muflag) {
      double **mu = atom->mu;
      double **t = atom->torque;
      double tx, ty, tz;
      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;
          tx = ez * mu[i][1] - ey * mu[i][2];
          ty = ex * mu[i][2] - ez * mu[i][0];
          tz = ey * mu[i][0] - ex * mu[i][1];
          t[i][0] += tx;
          t[i][1] += ty;
          t[i][2] += tz;
          fsum[0] -= mu[i][0] * ex + mu[i][1] * ey + mu[i][2] * ez;
        }
    }

    // variable efield, wrap with clear/add
    // potential energy = evar if defined, else 0.0

  } else {

    update_efield_variables();

    // charge interactions
    // force = qE

    if (qflag) {
      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 == ATOM) {
            fx = qe2f * q[i] * efield[i][0];
          } else {
            fx = q[i] * ex;
          }
          f[i][0] += fx;
          fsum[1] += fx;
          if (ystyle == ATOM) {
            fy = qe2f * q[i] * efield[i][1];
          } else {
            fy = q[i] * ey;
          }
          f[i][1] += fy;
          fsum[2] += fy;
          if (zstyle == ATOM) {
            fz = qe2f * q[i] * efield[i][2];
          } else {
            fz = q[i] * ez;
          }
          f[i][2] += fz;
          fsum[3] += fz;
          if (pstyle == ATOM) fsum[0] += qe2f * q[i] * efield[i][3];
          else if (estyle == ATOM) fsum[0] += efield[i][3];
        }
    }

    // dipole interactions
    // no force, torque = mu cross E

    if (muflag) {
      double **mu = atom->mu;
      double **t = atom->torque;
      double tx, ty, tz;
      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;
          tx = ez * mu[i][1] - ey * mu[i][2];
          ty = ex * mu[i][2] - ez * mu[i][0];
          tz = ey * mu[i][0] - ex * mu[i][1];
          t[i][0] += tx;
          t[i][1] += ty;
          t[i][2] += tz;
        }
    }
  }
}

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

void FixEfield::post_force_respa(int vflag, int ilevel, int /*iloop*/)
{
  if (ilevel == ilevel_respa) post_force(vflag);
}

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

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

/* ----------------------------------------------------------------------
   memory usage of local atom-based array
------------------------------------------------------------------------- */

double FixEfield::memory_usage()
{
  double bytes = 0.0;
  if (varflag == ATOM) bytes = atom->nmax * 4 * sizeof(double);
  return bytes;
}

/* ----------------------------------------------------------------------
   return energy added by fix
------------------------------------------------------------------------- */

double FixEfield::compute_scalar()
{
  if (force_flag == 0) {
    MPI_Allreduce(fsum, fsum_all, 4, MPI_DOUBLE, MPI_SUM, world);
    force_flag = 1;
  }
  return fsum_all[0];
}

/* ----------------------------------------------------------------------
   return total extra force due to fix
------------------------------------------------------------------------- */

double FixEfield::compute_vector(int n)
{
  if (force_flag == 0) {
    MPI_Allreduce(fsum, fsum_all, 4, MPI_DOUBLE, MPI_SUM, world);
    force_flag = 1;
  }
  return fsum_all[n + 1];
}

/* ----------------------------------------------------------------------
   update efield variables without doing anything else
   called by fix_qeq_reaxff
------------------------------------------------------------------------- */

void FixEfield::update_efield_variables()
{
  modify->clearstep_compute();

  if (xstyle == EQUAL) {
    ex = qe2f * input->variable->compute_equal(xvar);
  } else if (xstyle == ATOM) {
    input->variable->compute_atom(xvar, igroup, &efield[0][0], 4, 0);
  }
  if (ystyle == EQUAL) {
    ey = qe2f * input->variable->compute_equal(yvar);
  } else if (ystyle == ATOM) {
    input->variable->compute_atom(yvar, igroup, &efield[0][1], 4, 0);
  }
  if (zstyle == EQUAL) {
    ez = qe2f * input->variable->compute_equal(zvar);
  } else if (zstyle == ATOM) {
    input->variable->compute_atom(zvar, igroup, &efield[0][2], 4, 0);
  }
  if (pstyle == ATOM) input->variable->compute_atom(pvar, igroup, &efield[0][3], 4, 0);
  else if (estyle == ATOM) input->variable->compute_atom(evar, igroup, &efield[0][3], 4, 0);

  modify->addstep_compute(update->ntimestep + 1);
}