/**
  Signal is a demo element.
  \color #ac3
  \symbol Sg
  \symmetries all
*/
element Signal{
  DebugUtils du;
  EventWindow ew;
  AtomUtils au;
  Random rm;
  Unsigned(6) density;
  Void diffuse(){
    if(ew[1] is Empty){
      ew.swap(0,1);
    }
  }
  Bool chkDense(){
    WindowServices ws;
    ws.reset(0,4);
    Signal s;
    Int st=au.getType((Atom) s);
    if(ws.scan(st)){
      density=ws.getHits(0);
      if(density<=1){
        return false;
      }
    }
    return true;
  }
  Void catchRequest(){
    WindowServices ws;
    Random rdm;
    ws.reset(1,4);
    Request r;
    Int rt=au.getType((Atom) r);
    for(Int slot=ws.next();slot>=0;slot=ws.next()){
      Atom a= ew[slot];
      if(a is Request){
        Request you=(Request) a;
        if(density>you.density){
          if(rdm.oneIn(2)){
            ew.swap(0,slot);
          }
        }
      }
    }
  }
  Void behave(){
    Bool isAlive=true;
    if(chkDense()){// if alone, I can walk around. I store the number of Signals that I observed. 
      diffuse();
    }
    else{          // if I am alone, I have some chance to disappear.
      if(rm.oneIn(density*5-4)){
        Empty e;
        ew[0]=e;
        isAlive=false;
      }
    }
    if(isAlive){
      catchRequest(); // if not disappear, I will swap position with some Request who observe  
                      // less Signal than me.
    }
  }
}