#include <math.h>

#include <string.h>

#include <helianthus.h>

#define MAXCOUNT 10000

#define STEP     1.001

#define SPEED    2000

typedef struct Star {

  double cx, cy;

  double dx, dy;

  double r;

  int visible;

} Star;

Star stars[MAXCOUNT];

double step;

void updateStar(Star *s, double k, double w, double h) {

  s->dx *= k;

  s->dy *= k;

  s->r *= k;

  s->visible = fabs(s->dx + s->cx) + s->r < w/2

            && fabs(s->dy + s->cy) + s->r < h/2;

}

void update(double dt, double mx, double my, double w, double h) {

  step += SPEED*dt;

  while(step > 1) {

    int found = 0;

    for(int i = 0; i < MAXCOUNT; ++i) {

      if (stars[i].visible) updateStar(&stars[i], STEP, w, h);

      if (!found && !stars[i].visible) {

        stars[i].cx = mx;

        stars[i].cy = my;

        stars[i].dx = (randomFloat() - 0.5)*w - mx;

        stars[i].dy = (randomFloat() - 0.5)*h - my;

        stars[i].r = 0.25*pow(STEP, randomFloat());

        stars[i].visible = TRUE;

        found = 1;

      }

    }

    step -= 1;

  }

  double k = pow(STEP, step);

  for(int i = 0; i < MAXCOUNT; ++i)

    if (stars[i].visible) updateStar(&stars[i], k, w, h);

}

void init() {

  background(COLOR_BLACK);

}

void draw() {

  double w = windowGetWidth();

  double h = windowGetHeight();

  saveState();

  translate(w/2, h/2);

  update(windowGetFrameTime(), mouseTransformedX(), mouseTransformedY(), w, h);

  noStroke();

  fill(COLOR_WHITE);

  for(int i = 0; i < MAXCOUNT; ++i)

    if (stars[i].visible)

      circle(stars[i].cx + stars[i].dx, stars[i].cy + stars[i].dy, stars[i].r);

  restoreState();

}

int main() {

  windowSetResizable(TRUE);

  windowSetVariableFrameRate();

  windowSetInit(&init);

  windowSetDraw(&draw);

  windowRun();

}