package generator.gui;
import javax.swing.SwingUtilities;

/**
 * This is the 3rd version of SwingWorker (also known as
 * SwingWorker 3), an abstract class that you subclass to
 * perform GUI-related work in a dedicated thread.  For
 * instructions on using this class, see:
 *
 * http://java.sun.com/docs/books/tutorial/uiswing/misc/threads.html
 *
 * Note that the API changed slightly in the 3rd version:
 * You must now invoke start() on the SwingWorker after
 * creating it.
 */
public abstract class SwingWorker
{
    private Object value;  // see getValue(), setValue()
    private Thread thread;
    
    /**
     * Class to maintain reference to current worker thread
     * under separate synchronization control.
     */
    private static class ThreadVar
    {
        private Thread thread;
        ThreadVar(Thread t)
        { thread = t; }
        synchronized Thread get()
        { return thread; }
        synchronized void clear()
        { thread = null; }
    }
    
    private ThreadVar threadVar;
    
    /**
     * Get the value produced by the worker thread, or null if it
     * hasn't been constructed yet.
     */
    protected synchronized Object getValue()
    {
        return value;
    }
    
    /**
     * Set the value produced by worker thread
     */
    private synchronized void setValue(Object x)
    {
        value = x;
    }
    
    /**
     * Compute the value to be returned by the <code>get</code> method.
     */
    public abstract Object construct();
    
    /**
     * Called on the event dispatching thread (not on the worker thread)
     * after the <code>construct</code> method has returned.
     */
    public void finished()
    {
    }
    
    /**
     * A new method that interrupts the worker thread.  Call this method
     * to force the worker to stop what it's doing.
     */
    public void interrupt()
    {
        Thread t = threadVar.get();
        if (t != null)
        {
            t.interrupt();
        }
        threadVar.clear();
    }
    
    /**
     * Return the value created by the <code>construct</code> method.
     * Returns null if either the constructing thread or the current
     * thread was interrupted before a value was produced.
     *
     * @return the value created by the <code>construct</code> method
     */
    public Object get()
    {
        while (true)
        {
            Thread t = threadVar.get();
            if (t == null)
            {
                return getValue();
            }
            try
            {
                t.join();
            }
            catch (InterruptedException e)
            {
                Thread.currentThread().interrupt(); // propagate
                return null;
            }
        }
    }
    
    
    /**
     * Start a thread that will call the <code>construct</code> method
     * and then exit.
     */
    public SwingWorker()
    {
        final Runnable doFinished = new Runnable()
        {
            public void run()
            { finished(); }
        };
        
        Runnable doConstruct = new Runnable()
        {
            public void run()
            {
                try
                {
                    setValue(construct());
                }
                finally
                {
                    threadVar.clear();
                }
                
                SwingUtilities.invokeLater(doFinished);
            }
        };
        
        Thread t = new Thread(doConstruct);
        threadVar = new ThreadVar(t);
    }
    
    /**
     * Start the worker thread.
     */
    public void start()
    {
        Thread t = threadVar.get();
        if (t != null)
        {
            t.start();
        }
    }
}