package org.bukkit.craftbukkit.util;

import java.util.concurrent.ExecutionException;


public abstract class Waitable<T> implements Runnable
{
	private enum Status
	{
		WAITING,
		RUNNING,
		FINISHED,
	}

	Throwable t = null;
	T value = null;
	Status status = Status.WAITING;

	public final void run()
	{
		synchronized(this)
		{
			if(status != Status.WAITING)
			{
				throw new IllegalStateException("Invalid state " + status);
			}
			status = Status.RUNNING;
		}
		try
		{
			value = evaluate();
		} catch(Throwable t)
		{
			this.t = t;
		} finally
		{
			synchronized(this)
			{
				status = Status.FINISHED;
				this.notifyAll();
			}
		}
	}

	protected abstract T evaluate();

	public synchronized T get() throws InterruptedException, ExecutionException
	{
		while(status != Status.FINISHED)
		{
			this.wait();
		}
		if(t != null)
		{
			throw new ExecutionException(t);
		}
		return value;
	}
}