/*
 * Copyright (C) 2022 NHR@FAU, University Erlangen-Nuremberg.
 * All rights reserved. This file is part of MD-Bench.
 * Use of this source code is governed by a LGPL-3.0
 * license that can be found in the LICENSE file.
 */
#include <stdlib.h>
#include <stdio.h>
#include <math.h>

#include <neighbor.h>
#include <parameter.h>
#include <atom.h>
#include <util.h>
#include <mpi.h>

#define SMALL 1.0e-6
#define FACTOR 0.999

MD_FLOAT xprd, yprd, zprd;
MD_FLOAT bininvx, bininvy, bininvz;
int pad_x, pad_y, pad_z;
int nbinx, nbiny, nbinz;
int mbinx, mbiny, mbinz; // m bins in x, y, z
int *bincount;
int *bins;
int mbins;              //total number of bins
int atoms_per_bin;      // max atoms per bin
MD_FLOAT cutneigh;
MD_FLOAT cutneighsq;    // neighbor cutoff squared
int nmax;
int nstencil;           // # of bins in stencil
int* stencil;           // stencil list of bin offsets
MD_FLOAT binsizex, binsizey, binsizez;
int me;                 //rank
int method;             // method
int half_stencil;       //If half stencil exist 
int shellMethod;        //If shell method exist   

static int coord2bin(MD_FLOAT, MD_FLOAT , MD_FLOAT);
static MD_FLOAT bindist(int, int, int);
static int ghostZone(Atom*, int);
static int eightZone(Atom*, int);
static int halfZone(Atom*, int);
static void neighborGhost(Atom*, Neighbor*);
static inline int interaction(Atom* atom, int i, int j);

/* exported subroutines */
void initNeighbor(Neighbor *neighbor, Parameter *param) {
    MD_FLOAT neighscale = 5.0 / 6.0;
    xprd = param->nx * param->lattice;
    yprd = param->ny * param->lattice;
    zprd = param->nz * param->lattice;
    cutneigh = param->cutneigh;
    nbinx = neighscale * param->nx;
    nbiny = neighscale * param->ny;
    nbinz = neighscale * param->nz;
    nmax = 0;
    atoms_per_bin = 8;
    stencil = NULL;
    bins = NULL;
    bincount = NULL;
    neighbor->maxneighs = 100;
    neighbor->numneigh = NULL;
    neighbor->neighbors = NULL;
    //========== MPI =============
    shellMethod = 0;
    half_stencil = 0;
    method = param->method;
    if(method == halfShell || method == eightShell){ 
        param->half_neigh = 1;
        shellMethod = 1;
    }
    if(method == halfStencil){
        param->half_neigh = 0;
        half_stencil = 1;
    }
    me = 0;
    MPI_Comm_rank(MPI_COMM_WORLD,&me);
    neighbor->half_neigh = param->half_neigh;
    neighbor->Nshell = 0;  
    neighbor->numNeighShell = NULL;
    neighbor->neighshell = NULL;
    neighbor->listshell = NULL;
}

void setupNeighbor(Parameter* param) {
    MD_FLOAT coord;
    int mbinxhi, mbinyhi, mbinzhi;
    int nextx, nexty, nextz;

    if(param->input_file != NULL) {
        xprd = param->xprd;
        yprd = param->yprd;
        zprd = param->zprd;
    }
    // TODO: update lo and hi for standard case and use them here instead
    MD_FLOAT xlo = 0.0; MD_FLOAT xhi = xprd;
    MD_FLOAT ylo = 0.0; MD_FLOAT yhi = yprd;
    MD_FLOAT zlo = 0.0; MD_FLOAT zhi = zprd;

    cutneighsq = cutneigh * cutneigh;

    if(param->input_file != NULL) {
        binsizex = cutneigh * 0.5;
        binsizey = cutneigh * 0.5;
        binsizez = cutneigh * 0.5;
        nbinx = (int)((param->xhi - param->xlo) / binsizex);
        nbiny = (int)((param->yhi - param->ylo) / binsizey);
        nbinz = (int)((param->zhi - param->zlo) / binsizez);
        if(nbinx == 0) { nbinx = 1; }
        if(nbiny == 0) { nbiny = 1; }
        if(nbinz == 0) { nbinz = 1; }
        bininvx = nbinx / (param->xhi - param->xlo);
        bininvy = nbiny / (param->yhi - param->ylo);
        bininvz = nbinz / (param->zhi - param->zlo);
    } else {
        binsizex = xprd / nbinx;
        binsizey = yprd / nbiny;
        binsizez = zprd / nbinz;
        bininvx = 1.0 / binsizex;
        bininvy = 1.0 / binsizey;
        bininvz = 1.0 / binsizez;
    }
    pad_x = (int)(cutneigh*bininvx);
    while(pad_x * binsizex < FACTOR * cutneigh) pad_x++;
    pad_y = (int)(cutneigh*bininvy);
    while(pad_y * binsizey < FACTOR * cutneigh) pad_y++;
    pad_z = (int)(cutneigh*bininvz);
    while(pad_z * binsizez < FACTOR * cutneigh) pad_z++;

    nextx = (int) (cutneigh * bininvx);
    if(nextx * binsizex < FACTOR * cutneigh){
        nextx++;
        pad_x++;
    } 
    nexty = (int) (cutneigh * bininvy);
    if(nexty * binsizey < FACTOR * cutneigh){
        nexty++;
        pad_y++;
    } 
    nextz = (int) (cutneigh * bininvz);
    if(nextz * binsizez < FACTOR * cutneigh){
        nextz++;
        pad_z++;
    } 

    mbinx = nbinx+4*pad_x;
    mbiny = nbiny+4*pad_y;
    mbinz = nbinz+4*pad_z;

    if (stencil) { free(stencil); }
    stencil = (int*) malloc((2 * nextz + 1) * (2 * nexty + 1) * (2 * nextx + 1) * sizeof(int));
    nstencil = 0;
 
    int kstart = -nextz;
    int jstart = -nexty; 
    int istart = -nextx;
    int ibin = 0;
    for(int k = kstart; k <= nextz; k++) {
        for(int j = jstart; j <= nexty; j++) {
            for(int i = istart; i <= nextx; i++) {
                if(bindist(i, j, k) < cutneighsq) {     
                    int jbin = k * mbiny * mbinx + j * mbinx + i;
                    if(ibin>jbin && half_stencil) continue;                  
                    stencil[nstencil++] = jbin;
                }
            }
        }
    }

    mbins = mbinx * mbiny * mbinz;
    if (bincount) { free(bincount); }
    bincount = (int*) malloc(mbins * sizeof(int));
    if (bins) { free(bins); }
    bins = (int*) malloc(mbins * atoms_per_bin * sizeof(int));
}

void buildNeighbor_cpu(Atom *atom, Neighbor *neighbor) {
    int nall = atom->Nlocal + atom->Nghost;  
    /* extend atom arrays if necessary */
    if(nall > nmax) {
        nmax = nall;
        if(neighbor->numneigh) free(neighbor->numneigh);
        if(neighbor->neighbors) free(neighbor->neighbors);
        neighbor->numneigh = (int*) malloc(nmax * sizeof(int));
        neighbor->neighbors = (int*) malloc(nmax * neighbor->maxneighs * sizeof(int*));
    }
    /* bin local & ghost atoms */
    binatoms(atom);
    int resize = 1;
    /* loop over each atom, storing neighbors */
    while(resize) {
        int new_maxneighs = neighbor->maxneighs;
        resize = 0;
        for(int i = 0; i < atom->Nlocal; i++) {
            int* neighptr = &(neighbor->neighbors[i * neighbor->maxneighs]);
            int n = 0;
            MD_FLOAT xtmp = atom_x(i);
            MD_FLOAT ytmp = atom_y(i);
            MD_FLOAT ztmp = atom_z(i);
            int ibin = coord2bin(xtmp, ytmp, ztmp);
            #ifdef EXPLICIT_TYPES
            int type_i = atom->type[i];
            #endif

            for(int k = 0; k < nstencil; k++) {
                int jbin = ibin + stencil[k];
                int* loc_bin = &bins[jbin * atoms_per_bin];
                for(int m = 0; m < bincount[jbin]; m++) {    
                    int j = loc_bin[m];
                    
                    if((j==i) || (neighbor->half_neigh && (j<i))) 
                        continue;              
                    if(half_stencil && ibin==jbin  && !interaction(atom,i,j))
                        continue;          
                
                    MD_FLOAT delx = xtmp - atom_x(j);
                    MD_FLOAT dely = ytmp - atom_y(j);  
                    MD_FLOAT delz = ztmp - atom_z(j);
                    MD_FLOAT rsq = delx * delx + dely * dely + delz * delz;
                    #ifdef EXPLICIT_TYPES
                    int type_j = atom->type[j];
                    const MD_FLOAT cutoff = atom->cutneighsq[type_i * atom->ntypes + type_j];
                    #else
                    const MD_FLOAT cutoff = cutneighsq;
                    #endif
                    if(rsq <= cutoff) {
                        neighptr[n++] = j;
                    }
                }
            }
            neighbor->numneigh[i] = n;
            
            if(n >= neighbor->maxneighs) {
                resize = 1;

                if(n >= new_maxneighs) {
                    new_maxneighs = n;
                }
            }
        }
        if(resize) {
            printf("RESIZE %d, PROC %d\n", neighbor->maxneighs,me);
            neighbor->maxneighs = new_maxneighs * 1.2;
            free(neighbor->neighbors);
            neighbor->neighbors = (int*) malloc(atom->Nmax * neighbor->maxneighs * sizeof(int));
        }
    }

    if(method == eightShell) neighborGhost(atom, neighbor);
}

/* internal subroutines */
MD_FLOAT bindist(int i, int j, int k) {
    MD_FLOAT delx, dely, delz;

    if(i > 0) {
        delx = (i - 1) * binsizex;
    } else if(i == 0) {
        delx = 0.0;
    } else {
        delx = (i + 1) * binsizex;
    }

    if(j > 0) {
        dely = (j - 1) * binsizey;
    } else if(j == 0) {
        dely = 0.0;
    } else {
        dely = (j + 1) * binsizey;
    }

    if(k > 0) {
        delz = (k - 1) * binsizez;
    } else if(k == 0) {
        delz = 0.0;
    } else {
        delz = (k + 1) * binsizez;
    }
    return (delx * delx + dely * dely + delz * delz);
}

int coord2bin(MD_FLOAT xin, MD_FLOAT yin, MD_FLOAT zin) {
   int ix, iy, iz;
   MD_FLOAT eps = 1e-9; 
   MD_FLOAT xlo=0.0; MD_FLOAT ylo=0.0; MD_FLOAT zlo=0.0;
   xlo = fabs(xlo - pad_x*binsizex)+eps;
   ylo = fabs(ylo - pad_y*binsizey)+eps;
   zlo = fabs(zlo - pad_z*binsizez)+eps;
   ix = (int) ((xin + xlo)*bininvx);
   iy = (int) ((yin + ylo)*bininvy);
   iz = (int) ((zin + zlo)*bininvz);
    
    return (iz * mbiny * mbinx + iy * mbinx + ix);
    //return (iz * mbiny * mbinx + iy * mbinx + ix + 1);
}

void binatoms(Atom *atom) {    
    int nall = atom->Nlocal + atom->Nghost;
    int resize = 1;
    
    while(resize > 0) {
        resize = 0;

        for(int i = 0; i < mbins; i++) {
            bincount[i] = 0;
        }

        for(int i = 0; i < nall; i++) {
            int ibin = coord2bin(atom_x(i), atom_y(i), atom_z(i));
            if(shellMethod && !ghostZone(atom, i)) continue; 
            if(bincount[ibin] < atoms_per_bin) {
                int ac = bincount[ibin]++;
                bins[ibin * atoms_per_bin + ac] = i;
            } else {
                resize = 1;
            }
        }

        if(resize) {
            free(bins);
            atoms_per_bin *= 2;
            bins = (int*) malloc(mbins * atoms_per_bin * sizeof(int));
        }
    }
}

void sortAtom(Atom* atom) {
    binatoms(atom);
    int Nmax = atom->Nmax;
    int* binpos = bincount;
    for(int i = 1; i < mbins; i++) {
        binpos[i] += binpos[i - 1];
    }
    #ifdef AOS
    MD_FLOAT* new_x = (MD_FLOAT*) malloc(Nmax * sizeof(MD_FLOAT) * 3);
    MD_FLOAT* new_vx = (MD_FLOAT*) malloc(Nmax * sizeof(MD_FLOAT) * 3);
    #else
    MD_FLOAT* new_x = (MD_FLOAT*) malloc(Nmax * sizeof(MD_FLOAT));
    MD_FLOAT* new_y = (MD_FLOAT*) malloc(Nmax * sizeof(MD_FLOAT));
    MD_FLOAT* new_z = (MD_FLOAT*) malloc(Nmax * sizeof(MD_FLOAT));
    MD_FLOAT* new_vx = (MD_FLOAT*) malloc(Nmax * sizeof(MD_FLOAT));
    MD_FLOAT* new_vy = (MD_FLOAT*) malloc(Nmax * sizeof(MD_FLOAT));
    MD_FLOAT* new_vz = (MD_FLOAT*) malloc(Nmax * sizeof(MD_FLOAT));
    #endif
    MD_FLOAT* old_x = atom->x; MD_FLOAT* old_y = atom->y; MD_FLOAT* old_z = atom->z;
    MD_FLOAT* old_vx = atom->vx; MD_FLOAT* old_vy = atom->vy; MD_FLOAT* old_vz = atom->vz;

    for(int mybin = 0; mybin < mbins; mybin++) {
        int start = mybin > 0 ? binpos[mybin - 1] : 0;
        int count = binpos[mybin] - start;
        for(int k = 0; k < count; k++) {
            int new_i = start + k;
            int old_i = bins[mybin * atoms_per_bin + k];
            #ifdef AOS
            new_x[new_i * 3 + 0] = old_x[old_i * 3 + 0];
            new_x[new_i * 3 + 1] = old_x[old_i * 3 + 1];
            new_x[new_i * 3 + 2] = old_x[old_i * 3 + 2];
            new_vx[new_i * 3 + 0] = old_vx[old_i * 3 + 0];
            new_vx[new_i * 3 + 1] = old_vx[old_i * 3 + 1];
            new_vx[new_i * 3 + 2] = old_vx[old_i * 3 + 2];
            #else
            new_x[new_i] = old_x[old_i];
            new_y[new_i] = old_y[old_i];
            new_z[new_i] = old_z[old_i];
            new_vx[new_i] = old_vx[old_i];
            new_vy[new_i] = old_vy[old_i];
            new_vz[new_i] = old_vz[old_i];
            #endif
        }
    }
    free(atom->x);
    free(atom->vx);
    atom->x = new_x;
    atom->vx = new_vx;
    #ifndef AOS
    free(atom->y);
    free(atom->z);
    free(atom->vy);
    free(atom->vz);
    atom->y = new_y;
    atom->z = new_z;
    atom->vy = new_vy;
    atom->vz = new_vz;
    #endif
}

/* internal subroutines 
Added with MPI*/

static int ghostZone(Atom* atom, int i){
    if(i<atom->Nlocal)  return 1;
    else if(method == halfShell)  return halfZone(atom,i);
    else if(method == eightShell) return eightZone(atom,i); 
    else return 0;  
}

static int eightZone(Atom* atom, int i)
{   
    //Mapping: 0->0, 1->1, 2->2, 3->6, 4->3, 5->5, 6->4, 7->7
    int zoneMapping[] = {0, 1, 2, 6, 3, 5, 4, 7};
    MD_FLOAT *hi = atom->mybox.hi;
    int zone = 0;

    if(BigOrEqual(atom_x(i),hi[_x])) {
        zone += 1;
    }
    if(BigOrEqual(atom_y(i),hi[_y])) {
        zone += 2;
    }
    if(BigOrEqual(atom_z(i),hi[_z])) {
        zone += 4;
    }   
    return zoneMapping[zone];
}

static int halfZone(Atom* atom, int i)
{   
    MD_FLOAT *hi = atom->mybox.hi;
    MD_FLOAT *lo = atom->mybox.lo;

    if(atom_x(i)<lo[_x] && atom_y(i)<hi[_y] && atom_z(i)<hi[_z]){
        return 0;
    } else if(atom_y(i)<lo[_y] && atom_z(i)<hi[_z]){
        return 0;
    } else if(atom_z(i)<lo[_z]){
        return 0;
    } else {
        return 1;
    }
}

static void neighborGhost(Atom *atom, Neighbor *neighbor) {
    int Nshell=0;
    int Nlocal = atom->Nlocal;
    int Nghost = atom->Nghost;
    if(neighbor->listshell) free(neighbor->listshell);
    neighbor->listshell = (int*) malloc(Nghost * sizeof(int));
    int* listzone  = (int*) malloc(8 * Nghost * sizeof(int));
    int countAtoms[8] = {0,0,0,0,0,0,0,0};
 
    //Selecting ghost atoms for interaction
   for(int i = Nlocal; i < Nlocal+Nghost; i++) {
        int izone = ghostZone(atom,i);
        int *list = &listzone[Nghost*izone];
        int n  = countAtoms[izone];
        list[n] = i;
        countAtoms[izone]++;     
    }

    for(int zone = 1; zone<=3; zone++){
        int *list = &listzone[Nghost*zone];
        for(int n=0; n<countAtoms[zone]; n++)
            neighbor->listshell[Nshell++] = list[n]; 
    }

    neighbor->Nshell = Nshell;
    if(neighbor->numNeighShell) free(neighbor->numNeighShell);
    if(neighbor->neighshell) free(neighbor->neighshell);
    neighbor->neighshell = (int*) malloc(Nshell * neighbor->maxneighs * sizeof(int));
    neighbor->numNeighShell = (int*) malloc(Nshell * sizeof(int));
    int resize = 1;

    while(resize)
    {
        resize = 0;
        for(int i = 0; i < Nshell; i++) {   
            int *neighshell = &(neighbor->neighshell[i*neighbor->maxneighs]); 
            int n = 0;  
            int iatom = neighbor->listshell[i];
            int izone = ghostZone(atom, iatom);
            MD_FLOAT xtmp = atom_x(iatom);
            MD_FLOAT ytmp = atom_y(iatom);
            MD_FLOAT ztmp = atom_z(iatom);
            int ibin = coord2bin(xtmp, ytmp, ztmp);
            
            #ifdef EXPLICIT_TYPES
            int type_i = atom->type[iatom];
            #endif

            for(int k = 0; k < nstencil; k++) {
                int jbin = ibin + stencil[k];
                int* loc_bin = &bins[jbin * atoms_per_bin];
                for(int m = 0; m < bincount[jbin]; m++) {    
                    int jatom = loc_bin[m];
                
                    int jzone = ghostZone(atom,jatom);

                    if(jzone <=izone) continue;
                    if(izone == 1 && (jzone==5||jzone==6||jzone==7)) continue;
                    if(izone == 2 && (jzone==4||jzone==6||jzone==7)) continue;
                    if(izone == 3 && (jzone==4||jzone==5||jzone==7)) continue;
    
                    MD_FLOAT delx = xtmp - atom_x(jatom);
                    MD_FLOAT dely = ytmp - atom_y(jatom);  
                    MD_FLOAT delz = ztmp - atom_z(jatom);
                    MD_FLOAT rsq = delx * delx + dely * dely + delz * delz;

                    #ifdef EXPLICIT_TYPES
                    int type_j = atom->type[jatom];
                    const MD_FLOAT cutoff = atom->cutneighsq[type_i * atom->ntypes + type_j];
                    #else
                    const MD_FLOAT cutoff = cutneighsq;
                    #endif
                    if(rsq <= cutoff) {
                        neighshell[n++] = jatom;
                    }
                }
            }         
            
            neighbor->numNeighShell[i] = n; 
            if(n >= neighbor->maxneighs){
                resize = 1;
                neighbor->maxneighs = n * 1.2;
                break;
            }  
        }
            
        if(resize) {
            free(neighbor->neighshell);
            neighbor->neighshell = (int*) malloc(Nshell * neighbor->maxneighs * sizeof(int));
        }
    }  
    free(listzone); 
}

static inline int interaction(Atom* atom, int i, int j) {
       
    if(i<j && j<atom->Nlocal) {
        return 1;
    } else if( atom_z(j)>atom_z(i) && j>=atom->Nlocal) {
        return 1;
    } else if(Equal(atom_z(j),atom_z(i)) && atom_y(j)<atom_y(i) && j>=atom->Nlocal){
        return 1;  
    } else if(Equal(atom_z(j),atom_z(i)) && Equal(atom_y(j),atom_y(i)) && atom_x(j)<atom_x(i) && j>=atom->Nlocal){
        return 1;
    }  else {
        return 0;
    }
}