// This file contains excerpts from the textbook Concrete
// Abstractions: An Introduction to Computer Science Using Scheme, by
// Max Hailperin, Barbara Kaiser, and Karl Knight, Copyright (c) 1998
// by the authors. Full text is available for free at
// http://www.gustavus.edu/+max/concrete-abstractions.html

public class PoltergeistThread extends Thread {

  private Puzzle puz;
  private boolean enabled;

  public PoltergeistThread(Puzzle p){
    puz = p;
  }
  
  public void run(){
    try{
      while(true){
        Thread.sleep(1000); // 1000 milliseconds = 1 second
        waitUntilEnabled();
        puz.pushRandomTile();
      }
    } catch(InterruptedException e){
      // If the thread is forcibly interrupted while sleeping,
      // an exception gets thrown that is caught here. However,
      // we can't really do anything, except stop running.
    }
  }

  // Warning: these two routines don't work, see below (in text) for why.
  private void waitUntilEnabled() throws InterruptedException {
    while(!enabled){
      wait();
    }
  }

  public void enable(){
    enabled = true;
    notify();
  }

  public void disable(){
    enabled = false;
  }
}