import java.util.concurrent.*;


/**
 * The Queue to be consumed by the Shovel. It is based on the ConcurrentLinkedQueue and made specifically for the Shovel class.
 * This class is Thread safe.
 * 
 * @author Ahmed Messaoud
 * @see ConcurrentLinkedQueue
 * @see Shovel
 */
public class ShovelQueue extends ConcurrentLinkedQueue<Truck> {
	private int size;
	private boolean available = true;
	
	public ShovelQueue(){
		super();
		size=0;
	}
	
	/* (non-Javadoc)
	 * @see java.util.concurrent.ConcurrentLinkedQueue#add(java.lang.Object)
	 */
	public synchronized boolean add(Truck t){
		if( !available ){
			try{
				wait();
			}catch( Exception e ){}
		}
		available = false;
		//check size, if there is waiting, then advise truck to idle
		if( size > 0){
			try{
				t.startIdleling();
			}catch(AlreadyIdlelingException e){}
		}
		size++;
		available = true;
		notify();
		return super.add(t);
	}
	
	/* (non-Javadoc)
	 * @see java.util.concurrent.ConcurrentLinkedQueue#poll()
	 */
	public synchronized Truck poll(){
		if( !available ){
			try{
				wait();
			}catch( Exception e ){}
		}
		available = false;
		//check if truck was idleling, if it was, stop the idleling
		if( super.peek() != null ){
			if( super.peek().isIdleling() ){
				try{
					super.peek().stopIdleling();
				}catch(NotIdlelingException e){}
			}
			size--;
		}
		available = true;
		notify();
		return super.poll();
	}
	
}