/* ----------------------------------------------------------------------
   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
   https://www.lammps.org/, 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: Tod A Pascal (Caltech)
------------------------------------------------------------------------- */

#include "improper_umbrella.h"

#include "atom.h"
#include "comm.h"
#include "error.h"
#include "force.h"
#include "math_const.h"
#include "memory.h"
#include "neighbor.h"

#include <cmath>

using namespace LAMMPS_NS;
using MathConst::DEG2RAD;
using MathConst::RAD2DEG;

static constexpr double TOLERANCE = 0.05;
static constexpr double SMALL = 0.001;

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

ImproperUmbrella::ImproperUmbrella(LAMMPS *_lmp) : Improper(_lmp)
{
  writedata = 1;
}

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

ImproperUmbrella::~ImproperUmbrella()
{
  if (allocated) {
    memory->destroy(setflag);
    memory->destroy(kw);
    memory->destroy(w0);
    memory->destroy(C);
  }
}

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

void ImproperUmbrella::compute(int eflag, int vflag)
{
  int i1, i2, i3, i4, n, type;
  double eimproper, f1[3], f2[3], f3[3], f4[3];
  double vb1x, vb1y, vb1z, vb2x, vb2y, vb2z, vb3x, vb3y, vb3z;
  double domega, c, a, s, projhfg, dhax, dhay, dhaz, dahx, dahy, dahz, cotphi;
  double ax, ay, az, ra2, rh2, ra, rh, rar, rhr, arx, ary, arz, hrx, hry, hrz;

  eimproper = 0.0;
  ev_init(eflag, vflag);

  double **x = atom->x;
  double **f = atom->f;
  int **improperlist = neighbor->improperlist;
  int nimproperlist = neighbor->nimproperlist;
  int nlocal = atom->nlocal;
  int newton_bond = force->newton_bond;

  for (n = 0; n < nimproperlist; n++) {
    i1 = improperlist[n][0];
    i2 = improperlist[n][1];
    i3 = improperlist[n][2];
    i4 = improperlist[n][3];
    type = improperlist[n][4];

    // 1st bond

    vb1x = x[i2][0] - x[i1][0];
    vb1y = x[i2][1] - x[i1][1];
    vb1z = x[i2][2] - x[i1][2];

    // 2nd bond

    vb2x = x[i3][0] - x[i1][0];
    vb2y = x[i3][1] - x[i1][1];
    vb2z = x[i3][2] - x[i1][2];

    // 3rd bond

    vb3x = x[i4][0] - x[i1][0];
    vb3y = x[i4][1] - x[i1][1];
    vb3z = x[i4][2] - x[i1][2];

    // c0 calculation
    // A = vb1 X vb2 is perpendicular to IJK plane

    ax = vb1y * vb2z - vb1z * vb2y;
    ay = vb1z * vb2x - vb1x * vb2z;
    az = vb1x * vb2y - vb1y * vb2x;
    ra2 = ax * ax + ay * ay + az * az;
    rh2 = vb3x * vb3x + vb3y * vb3y + vb3z * vb3z;
    ra = sqrt(ra2);
    rh = sqrt(rh2);
    if (ra < SMALL) ra = SMALL;
    if (rh < SMALL) rh = SMALL;

    rar = 1 / ra;
    rhr = 1 / rh;
    arx = ax * rar;
    ary = ay * rar;
    arz = az * rar;
    hrx = vb3x * rhr;
    hry = vb3y * rhr;
    hrz = vb3z * rhr;

    c = arx * hrx + ary * hry + arz * hrz;

    // error check

    if (c > 1.0 + TOLERANCE || c < (-1.0 - TOLERANCE)) problem(FLERR, i1, i2, i3, i4);

    if (c > 1.0) c = 1.0;
    if (c < -1.0) c = -1.0;

    s = sqrt(1.0 - c * c);
    if (s < SMALL) s = SMALL;
    cotphi = c / s;

    projhfg =
        (vb3x * vb1x + vb3y * vb1y + vb3z * vb1z) / sqrt(vb1x * vb1x + vb1y * vb1y + vb1z * vb1z);
    projhfg +=
        (vb3x * vb2x + vb3y * vb2y + vb3z * vb2z) / sqrt(vb2x * vb2x + vb2y * vb2y + vb2z * vb2z);
    if (projhfg > 0.0) {
      s *= -1.0;
      cotphi *= -1.0;
    }

    //  force and energy
    // if w0 = 0: E = k * (1 - cos w)
    // if w0 != 0: E = 0.5 * C (cos w - cos w0)^2, C = k/(sin(w0)^2

    if (w0[type] == 0.0) {
      if (eflag) eimproper = kw[type] * (1.0 - s);
      a = -kw[type];
    } else {
      domega = s - cos(w0[type]);
      a = 0.5 * C[type] * domega;
      if (eflag) eimproper = a * domega;
      a *= 2.0;
    }

    // dhax = diffrence between H and A in X direction, etc

    a = a * cotphi;
    dhax = hrx - c * arx;
    dhay = hry - c * ary;
    dhaz = hrz - c * arz;

    dahx = arx - c * hrx;
    dahy = ary - c * hry;
    dahz = arz - c * hrz;

    f2[0] = (dhay * vb1z - dhaz * vb1y) * rar * a;
    f2[1] = (dhaz * vb1x - dhax * vb1z) * rar * a;
    f2[2] = (dhax * vb1y - dhay * vb1x) * rar * a;

    f3[0] = (-dhay * vb2z + dhaz * vb2y) * rar * a;
    f3[1] = (-dhaz * vb2x + dhax * vb2z) * rar * a;
    f3[2] = (-dhax * vb2y + dhay * vb2x) * rar * a;

    f4[0] = dahx * rhr * a;
    f4[1] = dahy * rhr * a;
    f4[2] = dahz * rhr * a;

    f1[0] = -(f2[0] + f3[0] + f4[0]);
    f1[1] = -(f2[1] + f3[1] + f4[1]);
    f1[2] = -(f2[2] + f3[2] + f4[2]);

    // apply force to each of 4 atoms

    if (newton_bond || i1 < nlocal) {
      f[i1][0] += f1[0];
      f[i1][1] += f1[1];
      f[i1][2] += f1[2];
    }

    if (newton_bond || i2 < nlocal) {
      f[i2][0] += f3[0];
      f[i2][1] += f3[1];
      f[i2][2] += f3[2];
    }

    if (newton_bond || i3 < nlocal) {
      f[i3][0] += f2[0];
      f[i3][1] += f2[1];
      f[i3][2] += f2[2];
    }

    if (newton_bond || i4 < nlocal) {
      f[i4][0] += f4[0];
      f[i4][1] += f4[1];
      f[i4][2] += f4[2];
    }

    if (evflag) {

      // get correct 4-body geometry for virial tally

      vb1x = x[i1][0] - x[i2][0];
      vb1y = x[i1][1] - x[i2][1];
      vb1z = x[i1][2] - x[i2][2];

      vb2x = x[i3][0] - x[i2][0];
      vb2y = x[i3][1] - x[i2][1];
      vb2z = x[i3][2] - x[i2][2];

      vb3x = x[i4][0] - x[i3][0];
      vb3y = x[i4][1] - x[i3][1];
      vb3z = x[i4][2] - x[i3][2];

      ev_tally(i1, i2, i3, i4, nlocal, newton_bond, eimproper, f1, f2, f4, vb1x, vb1y, vb1z, vb2x,
               vb2y, vb2z, vb3x, vb3y, vb3z);
    }
  }
}

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

void ImproperUmbrella::allocate()
{
  allocated = 1;
  const int np1 = atom->nimpropertypes + 1;

  memory->create(kw, np1, "improper:kw");
  memory->create(w0, np1, "improper:w0");
  memory->create(C, np1, "improper:C");
  memory->create(setflag, np1, "improper:setflag");
  for (int i = 1; i < np1; i++) setflag[i] = 0;
}

/* ----------------------------------------------------------------------
   set coeffs for one type
------------------------------------------------------------------------- */

void ImproperUmbrella::coeff(int narg, char **arg)
{
  if (narg != 3) error->all(FLERR, "Incorrect args for improper coefficients");
  if (!allocated) allocate();

  int ilo, ihi;
  utils::bounds(FLERR, arg[0], 1, atom->nimpropertypes, ilo, ihi, error);

  double k_one = utils::numeric(FLERR, arg[1], false, lmp);
  double w_one = utils::numeric(FLERR, arg[2], false, lmp);

  // convert w0 from degrees to radians

  int count = 0;
  for (int i = ilo; i <= ihi; i++) {
    kw[i] = k_one;
    w0[i] = DEG2RAD * w_one;
    if (w_one == 0)
      C[i] = 1.0;
    else
      C[i] = kw[i] / (pow(sin(w0[i]), 2.0));
    setflag[i] = 1;
    count++;
  }

  if (count == 0) error->all(FLERR, "Incorrect args for improper coefficients");
}

/* ----------------------------------------------------------------------
   proc 0 writes out coeffs to restart file
------------------------------------------------------------------------- */

void ImproperUmbrella::write_restart(FILE *fp)
{
  fwrite(&kw[1], sizeof(double), atom->nimpropertypes, fp);
  fwrite(&w0[1], sizeof(double), atom->nimpropertypes, fp);
  fwrite(&C[1], sizeof(double), atom->nimpropertypes, fp);
}

/* ----------------------------------------------------------------------
   proc 0 reads coeffs from restart file, bcasts them
------------------------------------------------------------------------- */

void ImproperUmbrella::read_restart(FILE *fp)
{
  allocate();

  if (comm->me == 0) {
    utils::sfread(FLERR, &kw[1], sizeof(double), atom->nimpropertypes, fp, nullptr, error);
    utils::sfread(FLERR, &w0[1], sizeof(double), atom->nimpropertypes, fp, nullptr, error);
    utils::sfread(FLERR, &C[1], sizeof(double), atom->nimpropertypes, fp, nullptr, error);
  }
  MPI_Bcast(&kw[1], atom->nimpropertypes, MPI_DOUBLE, 0, world);
  MPI_Bcast(&w0[1], atom->nimpropertypes, MPI_DOUBLE, 0, world);
  MPI_Bcast(&C[1], atom->nimpropertypes, MPI_DOUBLE, 0, world);

  for (int i = 1; i <= atom->nimpropertypes; i++) setflag[i] = 1;
}

/* ----------------------------------------------------------------------
   proc 0 writes to data file
------------------------------------------------------------------------- */

void ImproperUmbrella::write_data(FILE *fp)
{
  for (int i = 1; i <= atom->nimpropertypes; i++)
    fprintf(fp, "%d %g %g\n", i, kw[i], RAD2DEG * w0[i]);
}