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

#include <math.h>
#include <string.h>
#include <stdlib.h>
#include "fix_bfield.h"
#include "atom.h"
#include "update.h"
#include "domain.h"
#include "comm.h"
#include "modify.h"
#include "force.h"
#include "input.h"
#include "variable.h"
#include "region.h"
#include "memory.h"
#include "error.h"

using namespace LAMMPS_NS;
using namespace FixConst;

enum{NONE,CONSTANT,EQUAL,ATOM};

#define SMALL 0.001
#define PI 3.14159265359

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

FixBfield::FixBfield(LAMMPS *lmp, int narg, char **arg) :
  Fix(lmp, narg, arg)
{
  if (narg < 6)
    error->all(FLERR,"Illegal fix bfield command");

  dynamic_group_allow = 0;
  vector_flag = 1;
  scalar_flag = 1;
  size_vector = 3;
  global_freq = 1;
  extvector = 1;
  extscalar = 1;

  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 {
    B[0] = 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 {
    B[1] = 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 {
    B[2] = force->numeric(FLERR,arg[5]);
    zstyle = CONSTANT;
  }

  // optional args
  iregion = -1;
  idregion = NULL;
  region = NULL;

  int iarg = 6;
  while (iarg < narg) {
    if (strcmp(arg[iarg],"region") == 0) {
      if (iarg+2 > narg) error->all(FLERR,"Illegal fix bfield command");
      iregion = domain->find_region(arg[iarg+1]);
      if (iregion == -1)
        error->all(FLERR,"Region ID for fix bfield does not exist");
      int n = strlen(arg[iarg+1]) + 1;
      idregion = new char[n];
      strcpy(idregion,arg[iarg+1]);
      iarg += 2;
    } 
    else error->all(FLERR,"Illegal fix bfield command");
  }

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

  maxatom = atom->nmax;
  memory->create(v0,maxatom,3,"v0:bfield");
}

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

FixBfield::~FixBfield()
{
  delete [] idregion;
  memory->destroy(v0);
}

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

int FixBfield::setmask()
{
  int mask = 0;
  mask |= THERMO_ENERGY;
  mask |= INITIAL_INTEGRATE;
  mask |= POST_INTEGRATE;
  mask |= POST_FORCE;
  return mask;
}

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

void FixBfield::init()
{
  qflag = bmuflag = 0;
  // charges needed for lorentz force
  if (atom->q_flag) qflag = 1;
//  if (atom->bmu_flag && atom->torque_flag) bmuflag = 1;
//  if (!qflag && !bmuflag)
//    error->all(FLERR,"Fix bfield requires atom attribute q or bmu");

  // check variables

  if (xstr) {
    xvar = input->variable->find(xstr);
    if (xvar < 0)
      error->all(FLERR,"Variable name for fix bfield 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 bfield is invalid style");
  }
  if (ystr) {
    yvar = input->variable->find(ystr);
    if (yvar < 0)
      error->all(FLERR,"Variable name for fix bfield 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 bfield is invalid style");
  }
  if (zstr) {
    zvar = input->variable->find(zstr);
    if (zvar < 0)
      error->all(FLERR,"Variable name for fix bfield 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 bfield is invalid style");
  }

  // set units
  // B-field input in Tesla (T) for all unit sets except LJ
  // LJ: B in tau*q/m
  if (strcmp(update->unit_style,"lj") == 0) 
    qBm2f = 1;
  else if (strcmp(update->unit_style,"real") == 0) 
    qBm2f = 1.60217646e-19 / 1.66054e-27 / 1e15; // coulomb per electron charge / kg per amu / fs per s
  else if (strcmp(update->unit_style,"metal") == 0) 
    qBm2f = 1.60217646e-19 / 1.66054e-27 / 1e12; // coulomb per electron charge / kg per amu / ps per s
  else if (strcmp(update->unit_style,"si") == 0) 
    qBm2f = 1 / 1 / 1; // coulomb per coulomb / kg per kg / s per s
  else if (strcmp(update->unit_style,"cgs") == 0) 
    qBm2f = 3.356e-10 / 1.66054e-24 / 1; // coulomb per statcoulomb / g per amu / s per s
  else if (strcmp(update->unit_style,"electron") == 0) 
    qBm2f = 1.60217646e-19 / 1.66054e-27 / 1e15; // coulomb per electron charge / kg per amu / fs per s
  else if (strcmp(update->unit_style,"micro") == 0) 
    qBm2f = 1e-12 / 1.66054e-12 / 1e6; // coulomb per picocoulomb / kg per picogram / ms per s
  else if (strcmp(update->unit_style,"nano") == 0) 
    qBm2f = 1.60217646e-19 / 1.66054e-6 / 1e9; // coulomb per electron charge / kg per attogram / ns per s
  else
    error->all(FLERR,"Illegal units in fix bfield");

   dtf = 0.5*update->dt*force->ftm2v;

  // order of pre_integrate fixes important
  // fix bfield needs current v(t)
  // so fix bfield should occur before other pre_integrate methods
  int bfield = 0;
 
  for (int i = 0; i < modify->nfix; i++){
    if (strcmp(modify->fix[i]->style,"bfield") == 0)
      bfield = 1; 
    if(modify->fix[i]->time_integrate){
      if(!bfield) 
       error->all(FLERR,"fix bfield must be defined before nve integrator.");
      if (strcmp(modify->fix[i]->style,"nve") == 0 || strcmp(modify->fix[i]->style,"nve/limit") || strcmp(modify->fix[i]->style,"nve/sphere") == 0) 
        break;
      else 
        error->all(FLERR,"fix bfield requires fix nve or nve/limit or nve/sphere.");
     }
  }

  // set index and check validity of region
  if (iregion >= 0) {
    iregion = domain->find_region(idregion);
    if (iregion == -1)
      error->all(FLERR,"Region ID for fix aveforce does not exist");
  }

  // variable flags
  if (xstyle == ATOM || ystyle == ATOM || zstyle == ATOM)
    error->all(FLERR,"Fix bfield cannot use atom-style variables");
  else if (xstyle == EQUAL || ystyle == EQUAL || zstyle == EQUAL)
    varflag = EQUAL;
  else varflag = CONSTANT;

if(qflag){

  // x,v update is for limit of weak B-field
  // will not work well for strong fields
  double max_omega = 2*PI*SMALL/update->dt; 
  double *q = atom->q;
  double *rmass = atom->rmass;
  double *mass = atom->mass;
  int *type = atom->type;
  int *mask = atom->mask;
  int nlocal = atom->nlocal;
  double dtfm, c1;

  if(rmass){
    for (int i = 0; i < nlocal; i++)
      if (mask[i] & groupbit) {

        dtfm = dtf / rmass[i];
        c1 = qBm2f*q[i]/rmass[i];
        omega[0] = c1*B[0];
        omega[1] = c1*B[1];
        omega[2] = c1*B[2];

        if(fabs(omega[0]) > max_omega || omega[1] > max_omega || omega[2] > max_omega) // Spreiter Eq. 1
          error->warning(FLERR,"fix bfield does not support strong magnetic fields");
        }
  }else{
    for (int i = 0; i < nlocal; i++)
      if (mask[i] & groupbit) {

        dtfm = dtf / mass[type[i]];
        c1 = qBm2f*q[i]/mass[type[i]];
        omega[0] = c1*B[0];
        omega[1] = c1*B[1];
        omega[2] = c1*B[2];

        if(fabs(omega[0]) > max_omega || omega[1] > max_omega || omega[2] > max_omega) // Spreiter Eq. 1
          error->warning(FLERR,"fix bfield does not support strong magnetic fields");
      }
 }
}
}

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

void FixBfield::setup(int vflag)
{
  if (strstr(update->integrate_style,"verlet"))
    post_force(vflag);
}

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

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

/* ----------------------------------------------------------------------
  save current velocites
  runs before update to 1/2 step velocity
------------------------------------------------------------------------- */

void FixBfield::initial_integrate(int vflag)
{
  if(!qflag)
    return;

  int nlocal = atom->nlocal;
  double **v = atom->v;
  double **f = atom->f;

  // reallocate v0 array if necessary
  if (nlocal > maxatom) {
    maxatom = atom->nmax;
    memory->destroy(v0);
    memory->create(v0,maxatom,3,"bfield:v0");
  }

  for (int i = 0; i < nlocal; i++){
    v0[i][0] = v[i][0]; 
    v0[i][1] = v[i][1]; 
    v0[i][2] = v[i][2]; 
  }
}

/* ----------------------------------------------------------------------
   update v,x for b-field
   v,x are analytically integrated
   Spreiter and Walter, J. Comp. Phys. 102-119 (1999)
------------------------------------------------------------------------- */
 
void FixBfield::post_integrate()
{
  if(!qflag)
    return;

  double **x = atom->x;
  double **v = atom->v;
  double **f = atom->f;
  double *q = atom->q;
  double *rmass = atom->rmass;
  double *mass = atom->mass;
  int *type = atom->type;
  int *mask = atom->mask;
  int nlocal = atom->nlocal;
  if (igroup == atom->firstgroup) nlocal = atom->nfirst;
  imageint *image = atom->image;
  double vx, vy, vz, c1;
  double fx,fy,fz;
  double dtfm;
  double dtv = update->dt;
  double dtv_omega0, dtv_omega1, dtv_omega2;
  double half_dtfm, half_dtv_omega0, half_dtv_omega1, half_dtv_omega2;  
  double unwrap[3];

  // update region if necessary

  if (iregion >= 0) {
    region = domain->regions[iregion];
    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;

  // constant bfield

  if (rmass) {

      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;

        dtfm = dtf / rmass[i];
        c1 = qBm2f*q[i] / rmass[i];

        omega[0] = c1*B[0];
        omega[1] = c1*B[1];
        omega[2] = c1*B[2];
        vx = v0[i][0];
        vy = v0[i][1];
        vz = v0[i][2];

        //velocity update
        dtv_omega0 = dtv*omega[0];
        dtv_omega1 = dtv*omega[1];
        dtv_omega2 = dtv*omega[2];
        half_dtfm = 0.5*dtfm;
        half_dtv_omega0 = 0.5*dtv_omega0; 
        half_dtv_omega1 = 0.5*dtv_omega1; 
        half_dtv_omega2 = 0.5*dtv_omega2; 

        // B0
        v[i][1] += dtv_omega0*(vz+half_dtfm*f[i][1]-half_dtv_omega0*vy);
        v[i][2] += -dtv_omega0*(vy+half_dtfm*f[i][0]+half_dtv_omega0*vz);
        // B1
        v[i][0] += -dtv_omega1*(vz+half_dtfm*f[i][0]+half_dtv_omega1*vx);
        v[i][2] += dtv_omega1*(vx+half_dtfm*f[i][1]-half_dtv_omega1*vz);
        // B2
        v[i][0] += dtv_omega2*(vy+half_dtfm*f[i][1]-half_dtv_omega2*vx);
        v[i][1] += -dtv_omega2*(vx+half_dtfm*f[i][0]+half_dtv_omega2*vy);

        // position update 
        // B0
        x[i][1] += (dtv*half_dtv_omega0*vz);
        x[i][2] += (-dtv*half_dtv_omega0*vy);
        // B1
        x[i][0] += (-dtv*half_dtv_omega1*vz);
        x[i][2] += (dtv*half_dtv_omega1*vx);
        // B2
        x[i][0] += (dtv*half_dtv_omega2*vy);
        x[i][1] += (-dtv*half_dtv_omega2*vx);

        // estimate total magnetic force for analysis
        // not used for dynamics
        fx = q[i]*(vy*B[2]-vz*B[1]);
        fy = q[i]*(vz*B[0]-vx*B[2]);
        fz = q[i]*(vx*B[1]-vy*B[0]);
        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;
        }
  
} else {

      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;
        dtfm = dtf / mass[type[i]];
        c1 = qBm2f*q[i]/mass[type[i]];
        //update for B-field
        omega[0] = c1*B[0];
        omega[1] = c1*B[1];
        omega[2] = c1*B[2];

        vx = v0[i][0];
        vy = v0[i][1];
        vz = v0[i][2];

        //velocity update
        dtv_omega0 = dtv*omega[0];
        dtv_omega1 = dtv*omega[1];
        dtv_omega2 = dtv*omega[2];
        half_dtfm = 0.5*dtfm;
        half_dtv_omega0 = 0.5*dtv_omega0; 
        half_dtv_omega1 = 0.5*dtv_omega1; 
        half_dtv_omega2 = 0.5*dtv_omega2; 

        // B0
        v[i][1] += dtv_omega0*(vz+half_dtfm*f[i][1]-half_dtv_omega0*vy);
        v[i][2] += -dtv_omega0*(vy+half_dtfm*f[i][0]+half_dtv_omega0*vz);
        // B1
        v[i][0] += -dtv_omega1*(vz+half_dtfm*f[i][0]+half_dtv_omega1*vx);
        v[i][2] += dtv_omega1*(vx+half_dtfm*f[i][1]-half_dtv_omega1*vz);
        // B2
        v[i][0] += dtv_omega2*(vy+half_dtfm*f[i][1]-half_dtv_omega2*vx);
        v[i][1] += -dtv_omega2*(vx+half_dtfm*f[i][0]+half_dtv_omega2*vy);

        // position update 
        // B0
        x[i][1] += (dtv*half_dtv_omega0*vz);
        x[i][2] += (-dtv*half_dtv_omega0*vy);
        // B1
        x[i][0] += (-dtv*half_dtv_omega1*vz);
        x[i][2] += (dtv*half_dtv_omega1*vx);
        // B2
        x[i][0] += (dtv*half_dtv_omega2*vy);
        x[i][1] += (-dtv*half_dtv_omega2*vx);

        // compute total magnetic force for analysis
        // not used for dynamics
        fx = q[i]*(vy*B[2]-vz*B[1]);
        fy = q[i]*(vz*B[0]-vx*B[2]);
        fz = q[i]*(vx*B[1]-vy*B[0]);
        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;
        }
/*
 C A/ps T = C Ang/ps N /(Amp m) = 100 N wychodzi fx, czyli podzielic na 100 zeby dostac w N
 eV/Ang jednostka sily w metal, = 1.6e-19 J/Ang = 1.6e-19 N m/1e-10 m= 1.6e-9 N, czyli 1N = (1eV/Ang)/1.6e-9
 czyli 0.01 u = (1ev/Ang)/1.6e-9, 1eV/ang = 1.6e-11 u        
*/        
  }
}
/* ----------------------------------------------------------------------
    no force, torque = bmu cross B
------------------------------------------------------------------------- */

void FixBfield::post_force(int vflag)
{
    if (!bmuflag) 
      return;

  int nlocal = atom->nlocal;
  int *mask = atom->mask;
  double **x = atom->x;
//  double **bmu = atom->bmu;
  double **t = atom->torque;
  double tx,ty,tz;

  //update region if necessary
  if (iregion >= 0) {
      region = domain->regions[iregion];
      region->prematch();
  }

  // fsum[0] = "potential energy" for added force
  force_flag = 0;

  if (varflag == EQUAL) {
    modify->clearstep_compute();
    if (xstyle == EQUAL) B[0] = input->variable->compute_equal(xvar);
    if (ystyle == EQUAL) B[1] = input->variable->compute_equal(yvar);
    if (zstyle == EQUAL) B[2] = input->variable->compute_equal(zvar);
    modify->addstep_compute(update->ntimestep + 1);
  }

  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 = B[2]*bmu[i][1] - B[1]*bmu[i][2];
      ty = B[0]*bmu[i][2] - B[2]*bmu[i][0];
      tz = B[1]*bmu[i][0] - B[0]*bmu[i][1];
      t[i][0] += tx;
      t[i][1] += ty;
      t[i][2] += tz;
      fsum[0] -= bmu[i][0]*B[0] + bmu[i][1]*B[1] + bmu[i][2]*B[2];
  */  }
}

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

double FixBfield::memory_usage()
{
  double bytes;
  bytes = atom->nmax*3 * sizeof(double); //v0
  return bytes;
}

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

double FixBfield::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 FixBfield::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];
}