/*******************************************************************************
 * Copyright (c) 2000, 2007 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.debug.internal.core;


import java.io.IOException;
import java.io.OutputStream;
import java.util.Vector;

import org.eclipse.debug.core.DebugPlugin;

/**
 * Writes to the input stream of a system process, 
 * queueing output if the stream is blocked.
 * 
 * The input stream monitor writes to system in via
 * an output stream.
 */
public class InputStreamMonitor {
	
	/**
	 * The stream which is being written to (connected to system in).
	 */
	private OutputStream fStream;
	/**
	 * The queue of output.
	 */
	private Vector fQueue;
	/**
	 * The thread which writes to the stream.
	 */
	private Thread fThread;
	/**
	 * A lock for ensuring that writes to the queue are contiguous
	 */
	private Object fLock;
	
	/**
	 * Whether the underlying output stream has been closed
	 */
	private boolean fClosed = false;
	
	/**
	 * Creates an input stream monitor which writes
	 * to system in via the given output stream.
	 * 
	 * @param stream output stream
	 */
	public InputStreamMonitor(OutputStream stream) {
		fStream= stream;
		fQueue= new Vector();
		fLock= new Object();
	}
	
	/**
	 * Appends the given text to the stream, or
	 * queues the text to be written at a later time
	 * if the stream is blocked.
	 * 
	 * @param text text to append
	 */
	public void write(String text) {
		synchronized(fLock) {
			fQueue.add(text);
			fLock.notifyAll();
		}
	}

	/**
	 * Starts a thread which writes the stream.
	 */
	public void startMonitoring() {
		if (fThread == null) {
			fThread= new Thread(new Runnable() {
				public void run() {
					write();
				}
			}, DebugCoreMessages.InputStreamMonitor_label); 
            fThread.setDaemon(true);
			fThread.start();
		}
	}
	
	/**
	 * Close all communications between this
	 * monitor and the underlying stream.
	 */
	public void close() {
		if (fThread != null) {
			Thread thread= fThread;
			fThread= null;
			thread.interrupt(); 
		}
	}
	
	/**
	 * Continuously writes to the stream.
	 */
	protected void write() {
		while (fThread != null) {
			writeNext();
		}
		if (!fClosed) {
			try {
			    fStream.close();
			} catch (IOException e) {
				DebugPlugin.log(e);
			}
		}
	}
	
	/**
	 * Write the text in the queue to the stream.
	 */
	protected void writeNext() {
		while (!fQueue.isEmpty() && !fClosed) {
			String text = (String)fQueue.firstElement();
			fQueue.removeElementAt(0);
			try {
				fStream.write(text.getBytes());
				fStream.flush();
			} catch (IOException e) {
				DebugPlugin.log(e);
			}
		}
		try {
			synchronized(fLock) {
				fLock.wait();
			}
		} catch (InterruptedException e) {
		}
	}

    /**
     * Closes the output stream attached to the standard input stream of this
     * monitor's process.
     * 
     * @exception IOException if an exception occurs closing the input stream
     */
    public void closeInputStream() throws IOException {
        if (!fClosed) {
            fClosed = true;
            fStream.close();
        } else {
            throw new IOException();
        }
        
    }
}