/* ----------------------------------------------------------------------
   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
   http://lammps.sandia.gov, 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: Christina Payne (Vanderbilt U)
                        Stan Moore (Sandia) for dipole terms
------------------------------------------------------------------------- */

#include "math.h"
#include "string.h"
#include "stdlib.h"
#include "fix_efield.h"
#include "atom.h"
#include "update.h"
#include "domain.h"
#include "comm.h"
#include "modify.h"
#include "force.h"
#include "respa.h"
#include "input.h"
#include "variable.h"
#include "memory.h"
#include "error.h"

using namespace LAMMPS_NS;
using namespace FixConst;

enum{NONE,CONSTANT,EQUAL,ATOM};

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

FixEfield::FixEfield(LAMMPS *lmp, int narg, char **arg) :
  Fix(lmp, narg, arg)
{
  if (narg != 6) error->all(FLERR,"Illegal fix efield command");

  vector_flag = 1;
  scalar_flag = 1;
  size_vector = 3;
  global_freq = 1;
  extvector = 1;
  extscalar = 1;

  qe2f = force->qe2f;
  xstr = ystr = zstr = NULL;

  if (strstr(arg[3],"v_") == arg[3]) {
    int n = strlen(&arg[3][2]) + 1;
    xstr = new char[n];
    strcpy(xstr,&arg[3][2]);
  } else {
    ex = qe2f * force->numeric(FLERR,arg[3]);
    xstyle = CONSTANT;
  }

  if (strstr(arg[4],"v_") == arg[4]) {
    int n = strlen(&arg[4][2]) + 1;
    ystr = new char[n];
    strcpy(ystr,&arg[4][2]);
  } else {
    ey = qe2f * force->numeric(FLERR,arg[4]);
    ystyle = CONSTANT;
  }

  if (strstr(arg[5],"v_") == arg[5]) {
    int n = strlen(&arg[5][2]) + 1;
    zstr = new char[n];
    strcpy(zstr,&arg[5][2]);
  } else {
    ez = qe2f * force->numeric(FLERR,arg[5]);
    zstyle = CONSTANT;
  }

  // optional args

  estr = NULL;

  int iarg = 6;
  while (iarg < narg) {
    if (strcmp(arg[iarg],"energy") == 0) {
      if (iarg+2 > narg) error->all(FLERR,"Illegal fix efield command");
      if (strstr(arg[iarg+1],"v_") == arg[iarg+1]) {
        int n = strlen(&arg[iarg+1][2]) + 1;
        estr = new char[n];
        strcpy(estr,&arg[iarg+1][2]);
      } else error->all(FLERR,"Illegal fix efield command");
      iarg += 2;
    } else error->all(FLERR,"Illegal fix efield command");
  }

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

  maxatom = 0;
  efield = NULL;
}

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

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

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

int FixEfield::setmask()
{
  int mask = 0;
  mask |= THERMO_ENERGY;
  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 efield requires atom attribute q or mu");

  // check variables

  if (xstr) {
    xvar = input->variable->find(xstr);
    if (xvar < 0) 
      error->all(FLERR,"Variable name for fix efield does not exist");
    if (input->variable->equalstyle(xvar)) xstyle = EQUAL;
    else if (input->variable->atomstyle(xvar)) xstyle = ATOM;
    else error->all(FLERR,"Variable for fix efield is invalid style");
  }
  if (ystr) {
    yvar = input->variable->find(ystr);
    if (yvar < 0) 
      error->all(FLERR,"Variable name for fix efield does not exist");
    if (input->variable->equalstyle(yvar)) ystyle = EQUAL;
    else if (input->variable->atomstyle(yvar)) ystyle = ATOM;
    else error->all(FLERR,"Variable for fix efield is invalid style");
  }
  if (zstr) {
    zvar = input->variable->find(zstr);
    if (zvar < 0) 
      error->all(FLERR,"Variable name for fix efield does not exist");
    if (input->variable->equalstyle(zvar)) zstyle = EQUAL;
    else if (input->variable->atomstyle(zvar)) zstyle = ATOM;
    else error->all(FLERR,"Variable for fix efield is invalid style");
  }
  if (estr) {
    evar = input->variable->find(estr);
    if (evar < 0) 
      error->all(FLERR,"Variable name for fix efield does not exist");
    if (input->variable->atomstyle(evar)) estyle = ATOM;
    else error->all(FLERR,"Variable for fix efield is invalid style");
  } else estyle = NONE;

  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 efield with dipoles cannot use atom-style variables");

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

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

  if (strstr(update->integrate_style,"respa"))
    nlevels_respa = ((Respa *) update->integrate)->nlevels;
}

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

void FixEfield::setup(int vflag)
{
  if (strstr(update->integrate_style,"verlet"))
    post_force(vflag);
  else {
    ((Respa *) update->integrate)->copy_flevel_f(nlevels_respa-1);
    post_force_respa(vflag,nlevels_respa-1,0);
    ((Respa *) update->integrate)->copy_f_flevel(nlevels_respa-1);
  }
}

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

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;
  tagint *image = atom->image;
  int nlocal = atom->nlocal;

  // reallocate efield array if necessary

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

  // 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;

  // constant efield

  if (varflag == CONSTANT) {
    double unwrap[3];

    // 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) {
          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;
        }
    }

    // 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) {
          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 {

    modify->clearstep_compute();

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

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

    // charge interactions
    // force = qE

    if (qflag) {
      for (int i = 0; i < nlocal; i++)
        if (mask[i] & groupbit) {
          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 (estyle == ATOM) fsum[0] += efield[0][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) {
          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 == nlevels_respa-1) 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(void)
{
  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];
}