/*******************************************************************************
 * Copyright (c) 2000, 2006 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.ecf.provider.filetransfer.util;

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InterruptedIOException;

/**
 * Wraps an input stream that blocks indefinitely to simulate timeouts on
 * read(), skip(), and close(). The resulting input stream is buffered and
 * supports retrying operations that failed due to an InterruptedIOException.
 * 
 * Supports resuming partially completed operations after an
 * InterruptedIOException REGARDLESS of whether the underlying stream does
 * unless the underlying stream itself generates InterruptedIOExceptions in
 * which case it must also support resuming. Check the bytesTransferred field to
 * determine how much of the operation completed; conversely, at what point to
 * resume.
 * 
 * @since 3.0
 */
public class TimeoutInputStream extends FilterInputStream {
	// unsynchronized variables
	private final long readTimeout; // read() timeout in millis
	private final long closeTimeout; // close() timeout in millis, or -1

	// requests for the thread (synchronized)
	private boolean closeRequested = false; // if true, close requested

	// responses from the thread (synchronized)
	private Thread thread; // if null, thread has terminated
	private byte[] iobuffer; // circular buffer
	private int head = 0; // points to first unread byte
	private int length = 0; // number of remaining unread bytes
	private IOException ioe = null; // if non-null, contains a pending exception
	private boolean waitingForClose = false; // if true, thread is waiting for
	// close()

	private boolean growWhenFull = false; // if true, buffer will grow when it

	// is full

	/**
	 * Creates a timeout wrapper for an input stream.
	 * 
	 * @param in
	 *            the underlying input stream
	 * @param bufferSize
	 *            the buffer size in bytes; should be large enough to mitigate
	 *            Thread synchronization and context switching overhead
	 * @param readTimeout
	 *            the number of milliseconds to block for a read() or skip()
	 *            before throwing an InterruptedIOException; 0 blocks
	 *            indefinitely
	 * @param closeTimeout
	 *            the number of milliseconds to block for a close() before
	 *            throwing an InterruptedIOException; 0 blocks indefinitely, -1
	 *            closes the stream in the background
	 */
	public TimeoutInputStream(InputStream in, int bufferSize, long readTimeout, long closeTimeout) {
		super(in);
		this.readTimeout = readTimeout;
		this.closeTimeout = closeTimeout;
		this.iobuffer = new byte[bufferSize];
		thread = new Thread(new Runnable() {
			public void run() {
				runThread();
			}
		}, "TimeoutInputStream");//$NON-NLS-1$
		thread.setDaemon(true);
		thread.start();
	}

	public TimeoutInputStream(InputStream in, int bufferSize, long readTimeout, long closeTimeout, boolean growWhenFull) {
		this(in, bufferSize, readTimeout, closeTimeout);
		this.growWhenFull = growWhenFull;
	}

	/**
	 * Wraps the underlying stream's method. It may be important to wait for a
	 * stream to actually be closed because it holds an implicit lock on a
	 * system resoure (such as a file) while it is open. Closing a stream may
	 * take time if the underlying stream is still servicing a previous request.
	 * 
	 * @throws InterruptedIOException
	 *             if the timeout expired
	 * @throws IOException
	 *             if an i/o error occurs
	 */
	public void close() throws IOException {
		Thread oldThread;
		synchronized (this) {
			if (thread == null)
				return;
			oldThread = thread;
			closeRequested = true;
			thread.interrupt();
			checkError();
		}
		if (closeTimeout == -1)
			return;
		try {
			oldThread.join(closeTimeout);
		} catch (InterruptedException e) {
			Thread.currentThread().interrupt(); // we weren't expecting to be
			// interrupted
		}
		synchronized (this) {
			checkError();
			if (thread != null)
				throw new InterruptedIOException();
		}
	}

	/**
	 * Returns the number of unread bytes in the buffer.
	 * 
	 * @throws IOException
	 *             if an i/o error occurs
	 */
	public synchronized int available() throws IOException {
		if (length == 0)
			checkError();
		return length > 0 ? length : 0;
	}

	/**
	 * Reads a byte from the stream.
	 * 
	 * @throws InterruptedIOException
	 *             if the timeout expired and no data was received,
	 *             bytesTransferred will be zero
	 * @throws IOException
	 *             if an i/o error occurs
	 */
	public synchronized int read() throws IOException {
		if (!syncFill())
			return -1; // EOF reached
		int b = iobuffer[head++] & 255;
		if (head == iobuffer.length)
			head = 0;
		length--;
		notify();
		return b;
	}

	/**
	 * Reads multiple bytes from the stream.
	 * 
	 * @throws InterruptedIOException
	 *             if the timeout expired and no data was received,
	 *             bytesTransferred will be zero
	 * @throws IOException
	 *             if an i/o error occurs
	 */
	public synchronized int read(byte[] buffer, int off, int len) throws IOException {
		if (!syncFill())
			return -1; // EOF reached
		int pos = off;
		if (len > length)
			len = length;
		while (len-- > 0) {
			buffer[pos++] = iobuffer[head++];
			if (head == iobuffer.length)
				head = 0;
			length--;
		}
		notify();
		return pos - off;
	}

	/**
	 * Skips multiple bytes in the stream.
	 * 
	 * @throws InterruptedIOException
	 *             if the timeout expired before all of the bytes specified have
	 *             been skipped, bytesTransferred may be non-zero
	 * @throws IOException
	 *             if an i/o error occurs
	 */
	public synchronized long skip(long count) throws IOException {
		long amount = 0;
		try {
			do {
				if (!syncFill())
					break; // EOF reached
				int skip = (int) Math.min(count - amount, length);
				head = (head + skip) % iobuffer.length;
				length -= skip;
				amount += skip;
			} while (amount < count);
		} catch (InterruptedIOException e) {
			e.bytesTransferred = (int) amount; // assumes amount <
			// Integer.MAX_INT
			throw e;
		}
		notify();
		return amount;
	}

	/**
	 * Mark is not supported by the wrapper even if the underlying stream does,
	 * returns false.
	 */
	public boolean markSupported() {
		return false;
	}

	/**
	 * Waits for the buffer to fill if it is empty and the stream has not
	 * reached EOF.
	 * 
	 * @return true if bytes are available, false if EOF has been reached
	 * @throws InterruptedIOException
	 *             if EOF not reached but no bytes are available
	 */
	private boolean syncFill() throws IOException {
		if (length != 0)
			return true;
		checkError(); // check errors only after we have read all remaining
		// bytes
		if (waitingForClose)
			return false;
		notify();
		try {
			wait(readTimeout);
		} catch (InterruptedException e) {
			Thread.currentThread().interrupt(); // we weren't expecting to be
			// interrupted
		}
		if (length != 0)
			return true;
		checkError(); // check errors only after we have read all remaining
		// bytes
		if (waitingForClose)
			return false;
		throw new InterruptedIOException();
	}

	/**
	 * If an exception is pending, throws it.
	 */
	private void checkError() throws IOException {
		if (ioe != null) {
			IOException e = ioe;
			ioe = null;
			throw e;
		}
	}

	/**
	 * Runs the thread in the background.
	 */
	void runThread() {
		try {
			readUntilDone();
		} catch (IOException e) {
			synchronized (this) {
				ioe = e;
			}
		} finally {
			waitUntilClosed();
			try {
				in.close();
			} catch (IOException e) {
				synchronized (this) {
					ioe = e;
				}
			} finally {
				synchronized (this) {
					thread = null;
					notify();
				}
			}
		}
	}

	/**
	 * Waits until we have been requested to close the stream.
	 */
	private synchronized void waitUntilClosed() {
		waitingForClose = true;
		notify();
		while (!closeRequested) {
			try {
				wait();
			} catch (InterruptedException e) {
				closeRequested = true; // alternate quit signal
			}
		}
	}

	/**
	 * Reads bytes into the buffer until EOF, closed, or error.
	 */
	private void readUntilDone() throws IOException {
		for (;;) {
			int off, len;
			synchronized (this) {
				while (isBufferFull()) {
					if (closeRequested)
						return; // quit signal
					waitForRead();
				}
				off = (head + length) % iobuffer.length;
				len = ((head > off) ? head : iobuffer.length) - off;
			}
			int count;
			try {
				// the i/o operation might block without releasing the lock,
				// so we do this outside of the synchronized block
				count = in.read(iobuffer, off, len);
				if (count == -1)
					return; // EOF encountered
			} catch (InterruptedIOException e) {
				count = e.bytesTransferred; // keep partial transfer
			}
			synchronized (this) {
				length += count;
				notify();
			}
		}
	}

	/*
	 * Wait for a read when the buffer is full (with the implication that space
	 * will become available in the buffer after the read takes place).
	 */
	private synchronized void waitForRead() {
		try {
			if (growWhenFull) {
				// wait a second before growing to let reads catch up
				wait(readTimeout);
			} else {
				wait();
			}
		} catch (InterruptedException e) {
			closeRequested = true; // alternate quit signal
		}
		// If the buffer is still full, give it a chance to grow
		if (growWhenFull && isBufferFull()) {
			growBuffer();
		}
	}

	private synchronized void growBuffer() {
		int newSize = 2 * iobuffer.length;
		if (newSize > iobuffer.length) {
			byte[] newBuffer = new byte[newSize];
			int pos = 0;
			int len = length;
			while (len-- > 0) {
				newBuffer[pos++] = iobuffer[head++];
				if (head == iobuffer.length)
					head = 0;
			}
			iobuffer = newBuffer;
			head = 0;
			// length instance variable was not changed by this method
		}
	}

	private boolean isBufferFull() {
		return length == iobuffer.length;
	}
}
