/* ----------------------------------------------------------------------
   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 authors: Frances Mackay, Santtu Ollila, Colin Denniston (UWO)
------------------------------------------------------------------------- */

#include "math.h"
#include "stdlib.h"
#include "string.h"
#include "fix_lb_viscous.h"
#include "atom.h"
#include "update.h"
#include "respa.h"
#include "error.h"
#include "fix_lb_fluid.h"
#include "modify.h"
#include "group.h"

using namespace LAMMPS_NS;
using namespace FixConst;

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

FixLbViscous::FixLbViscous(LAMMPS *lmp, int narg, char **arg) :
  Fix(lmp, narg, arg)
{
  if (narg < 3) error->all(FLERR,"Illegal fix lb/viscous command");

  int groupbit_lb_fluid = 0;
 
  for(int ifix=0; ifix<modify->nfix; ifix++)
    if(strcmp(modify->fix[ifix]->style,"lb/fluid")==0){
      fix_lb_fluid = (FixLbFluid *)modify->fix[ifix];
      groupbit_lb_fluid = group->bitmask[modify->fix[ifix]->igroup];
    }

  if(groupbit_lb_fluid == 0)
    error->all(FLERR,"the lb/fluid fix must also be used if using the lb/viscous fix");

  int *mask = atom->mask;
  int nlocal = atom->nlocal;
  for(int j=0; j<nlocal; j++){
    if((mask[j] & groupbit) && !(mask[j] & groupbit_lb_fluid))
      error->one(FLERR,"to apply a fluid force onto an atom, the lb/fluid fix must be used for that atom.");  
  }
 

}

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

FixLbViscous::~FixLbViscous()
{

}

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

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

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

void FixLbViscous::init()
{

  if (strcmp(update->integrate_style,"respa") == 0)
    nlevels_respa = ((Respa *) update->integrate)->nlevels;

}

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

void FixLbViscous::setup(int vflag)
{
  if (strcmp(update->integrate_style,"verlet") == 0)
    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 FixLbViscous::min_setup(int vflag)
{
  post_force(vflag);
}

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

void FixLbViscous::post_force(int vflag)
{
  // apply drag force to atoms in group
  // direction is opposed to velocity vector
  // magnitude depends on atom type

  double **f = atom->f;
  int *mask = atom->mask;
  int nlocal = atom->nlocal;
  double **hydroF = fix_lb_fluid->hydroF;

  for (int i = 0; i < nlocal; i++)
    if (mask[i] & groupbit) {
      f[i][0] += hydroF[i][0];
      f[i][1] += hydroF[i][1];
      f[i][2] += hydroF[i][2];

    }

}

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

void FixLbViscous::post_force_respa(int vflag, int ilevel, int iloop)
{
  if (ilevel == nlevels_respa-1) post_force(vflag);
}

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

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

