class DivModCalculator extends Observable{

  private DivModPresenterObs viewObject;

  IntPair inputMemory, outputMemory;

  public DivModCalculator(DivModPresenterObs viewObject) {
    this.viewObject = viewObject;
    addObserver(viewObject);
    inputMemory = null; outputMemory = null;
  }
   
  private IntPair divMod(int x, int y){
    // require x > 0 && y > 0 ;

    int rest = x;
    int quotient = 0;
    
    while (rest >= y) {
      // invariant rest + quotient * y = x ;
      rest = rest - y;
      quotient = quotient + 1;
    }
    return (new IntPair(quotient,rest));
    // ensure  rest + quotient * y = x && rest < y && rest >= 0 ;
  } // end div

  public void doCalculate(int input1, int input2){
    inputMemory = new IntPair(input1, input2);
    if (input1 > 0 && input2 > 0)
      outputMemory = divMod(input1, input2);
    else
      outputMemory = new IntPair(-1, -1);
    
    setChanged();       // now I am changed
    notifyObservers();  // ... and therefore I notifiy my observers
  }

  public IntPair getResult(){
    return outputMemory;
  }

} // end DivModCalculator