package com.ryanmichela.sshd;

import java.util.concurrent.ExecutionException;

/**
 * Copyright 2013 Ryan Michela
 */
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;
    }
}