package nbody;

class Body {

  float  G;

  int NUMPLANETS;

  float x, y;
  float ax, ay;
  float mass;
  float radius;
  array [Body] planets;
  int myIndex;
  Semaphore mySem;
  boolean sticky;

  constructor(float x_, float y_, float mass_, float radius_, float ax_, float ay_, 
    int index, Semaphore sem) {

    G = -9.7;
    NUMPLANETS = 64;
    sticky = false;

    x = x_;
    y = y_;
    mass = mass_;
    radius = radius_;
    ax = ax_;
    ay = ay_;
    planets = new Body[NUMPLANETS];
    myIndex = index;
    mySem = sem;
  }

  void assignBody( int index, Body partner ) {
    planets[index] = partner;
  }


  void move(){
    int size = NUMPLANETS;
    float dy,dx,rad,g,force,tempx,tempy;

    x = x + ax;
    y = y + ay;

    int jj = 0;
    while( jj < size ) {
      if((myIndex != jj)) {
        Body body = planets[jj];
        dx = x - body.x;
        dy = y - body.y;
        rad = dx*dx + dy*dy;

         if(rad <= (radius*radius + body.radius*body.radius)) {
          if(sticky){
            tempy = body.ay;
            tempx = body.ax;

            force =	body.mass * body.ax;
            body.ax = body.ax - force / mass;

            force =	body.mass * body.ay;
            body.ay = body.ay - force / mass;

            force = mass * tempx;
            ax = ax - force / body.mass;

            force = mass * tempy;
            ay = ay - force / body.mass;

          } else{
            tempy = ay;
            tempx = ax;

            force =	body.mass * body.ax;
            ax = ax + force / mass;

            force =	body.mass * body.ay;
            ay = ay + force / mass;

            force = mass * tempx;
            body.ax = body.ax + force / body.mass;

            force = mass * tempy;
            body.ay = body.ay + force / body.mass;

          }

        }

        g = G * body.mass / rad;
        rad = sqrt(rad);

        ax = ax + g * (dx/rad);
        ay = ay + g * (dy/rad);
      }
      jj = jj + 1;
    }

    mySem.signal();
  }

}

class SimEngine {
  int NUMPLANETS;

  float xsize;
  float ysize;
  float  G;

  array[Body] bodies;
  array[Semaphore] sem0;
  array[Semaphore] sem1;
  array[Semaphore] sem2;
  array[Semaphore] sem3;
  array[Semaphore] sem4;
  array[Semaphore] sem5;

  int numIter;
  int iter;

  constructor() {
    int i;
    int j;
    Semaphore sem;
    Semaphore semA;
    Semaphore semB;

    NUMPLANETS = 64;
    xsize = 400.0;
    ysize = 400.0;
    G = -9.7;
    numIter = 100;
    iter = 0;

    bodies = new Body[NUMPLANETS];
    sem0 = new Semaphore[NUMPLANETS/2];
    i = 0;
    while( i < NUMPLANETS ) {
      sem = new Semaphore(false, this, true);
      if( i == 20 ) {
        bodies[i] = new Body(frandom() * xsize, frandom() * ysize, 500.0, 5.0, 0.0, 0.0, i, sem);
      } else {
        bodies[i] = new Body(frandom() * xsize, frandom() * ysize, 1.0, 1.0, 0.0001 * G * G, 0.0001 * G * G, i, sem);
      }
      i = i + 1;
      bodies[i] = new Body(frandom() * xsize, frandom() * ysize, 1.0, 0.01, 0.0001 * G * G, 0.0001 * G * G, i, sem);
      i = i + 1;
      sem.assignLeaves(bodies[i-2],bodies[i-1]);
      sem0[i/2 - 1] = sem;
    }
    i = 0;
    while( i < NUMPLANETS ) {
      j = 0;
      while( j < NUMPLANETS ) {
        Body b;
	b = bodies[i];
        b.assignBody(j, bodies[j]);
        j = j + 1;
      }
      i = i + 1;
    }
    i = 0;
    sem1 = new Semaphore[NUMPLANETS/4];
    while( i < NUMPLANETS / 2 ) {
      sem = new Semaphore(false, this, false);
      semA = sem0[i];
      i = i + 1;
      semB = sem0[i];
      i = i + 1;
      sem.assignChildren(semA, semB);
      semA.assignParent(sem);
      semB.assignParent(sem);
      sem1[i/2 - 1] = sem;
    }
    i = 0;
    sem2 = new Semaphore[NUMPLANETS/8];
    while( i < NUMPLANETS / 4 ) {
      sem = new Semaphore(false, this, false);
      semA = sem1[i];
      i = i + 1;
      semB = sem1[i];
      i = i + 1;
      sem.assignChildren(semA, semB);
      semA.assignParent(sem);
      semB.assignParent(sem);
      sem2[i/2 - 1] = sem;
    }
    i = 0;
    sem3 = new Semaphore[NUMPLANETS/16];
    while( i < NUMPLANETS / 8 ) {
      sem = new Semaphore(false, this, false);
      semA = sem2[i];
      i = i + 1;
      semB = sem2[i];
      i = i + 1;
      sem.assignChildren(semA, semB);
      semA.assignParent(sem);
      semB.assignParent(sem);
      sem3[i/2 - 1] = sem;
    }
    i = 0;
    sem4 = new Semaphore[NUMPLANETS/32];
    while( i < NUMPLANETS / 16 ) {
      sem = new Semaphore(false, this, false);
      semA = sem3[i];
      i = i + 1;
      semB = sem3[i];
      i = i + 1;
      sem.assignChildren(semA, semB);
      semA.assignParent(sem);
      semB.assignParent(sem);
      sem4[i/2 - 1] = sem;
    }
    i = 0;
    sem5 = new Semaphore[NUMPLANETS/64];
    while( i < 2 ) {
      sem = new Semaphore(true, this, false);
      semA = sem4[i];
      i = i + 1;
      semB = sem4[i];
      i = i + 1;
      sem.assignChildren(semA, semB);
      semA.assignParent(sem);
      semB.assignParent(sem);
      sem5[i/2 - 1] = sem;
    }
  }

  void signal() {
    if( iter < numIter ) {
      iter = iter + 1;
      Semaphore s = sem5[0];
      s.go();
    } else {
      prints("done");
    }
  }

  void step() {
    iter = numIter;
    Semaphore s = sem5[0];
    s.go();
  }

  void start() {
    iter = 0;
    Semaphore s = sem5[0];
    s.go();
  }
}

class Semaphore {

  int semCount;
  Semaphore parent;
  boolean top;
  boolean bottom;
  SimEngine se;
  Body child1, child2;
  Semaphore sem1, sem2;

  constructor(boolean isTop, SimEngine eng, boolean isBot) {
    semCount = 0;
    top = isTop;
    se = eng;
    bottom = isBot;
  }

  void assignParent( Semaphore par ) {
    parent = par;
  }

  void assignChildren( Semaphore s1, Semaphore s2 ) {
    sem1 = s1;
    sem2 = s2;
  }
  void assignLeaves( Body c1, Body c2 ) {
    child1 = c1;
    child2 = c2;
  }

  void go() {
    if( bottom ) {
      child1.move();
      child2.move();
    } else {
      sem1.go();
      sem2.go();
    }
  }

  void signal() {
    semCount = semCount + 1;
    if( semCount == 2 ) {
      semCount = 0;
      if( !top ) {
        parent.signal();
      }
      if( top ) {
        se.signal();
      }
    }
  }
}

float frandom() {
    return frand();
}

void main() {
    SimEngine se;
  
    prints("init nbody...");
    se = new SimEngine();

    prints("starting nbody...");
    se.start();
}