// PROGRAM random_walk2
// 2次元のランダムウォーク

#include "TrueBASIC.h"
#include "csgraphics.h"

int main();
void initial(int x[], int y[], int *N, int *nwalkers, int *im);
void move(int x[], int y[], int nwalkers, int im);
void choice(int x[], int y[], int i);

int main()
{
    int N, nwalkers, step, im;
    float X1, Y1, X2, Y2;
    int x[501], y[501];
    char Stmp1_[_LBUFF_];

    GWopen(0);

    initial(x, y, &N, &nwalkers, &im);
    GWsetogn(0, 1);
    GWgetwn(&X1, &Y1, &X2, &Y2);
    X1 = X1+(X2-X1)/80;
    Y1 = Y2-(Y2-Y1)/24;
    for(step = 1; step <= N; ++step)
    {
        GWsetogn(0, -2);
        sprintf(Stmp1_, "%d", step);
        GWputtxt(X1, Y1, Stmp1_);
        move(x, y, nwalkers, im);
        GWflush(-2);
    }

    GWquit();
    return 0;
}

void initial(int x[], int y[], int *N, int *nwalkers, int *im)
{
    int i;
    double r;
    float xwin, ywin;
    char Stmp1_[_LBUFF_];

    rnd(-1);
    printf("number of walkers = ");
    fgets(Stmp1_, _LBUFF_, stdin);
    sscanf(Stmp1_, "%d", nwalkers);
    printf("total number of steps = ");
    fgets(Stmp1_, _LBUFF_, stdin);
    sscanf(Stmp1_, "%d", N);
    compute_aspect_ratio((float)(sqrt((double)(*N)*2)*2), &xwin, &ywin);
    GWindow(-xwin, -ywin, xwin, ywin);
    // 原点に N 個の粒子を置く
    r = 0.5;
    *im = GWcmbmrk(0, 1, (float)(2*r), RED, -1, -1);
    for(i = 1; i <= (*nwalkers); ++i)
    {
        x[i] = 0;
        y[i] = 0;
    }
}

void move(int x[], int y[], int nwalkers, int im)
{
    int i;

    for(i = 1; i <= nwalkers; ++i)
    {
        choice(x, y, i);
        GWputcmb(im, (float)(x[i]), (float)(y[i]), 0.0f, 0.0f, 0);
    }
}

void choice(int x[], int y[], int i)
{
    double p;

    p = rnd(0);
    if(p <= 0.25)
        ++x[i];
    else if(p <= 0.5)
        --x[i];
    else if(p <= 0.75)
        --y[i];
    else
        ++y[i];
}