/*
 * Copyright (C) 2016, Google Inc.
 * and other copyright owners as documented in the project's IP log.
 *
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Distribution License v1.0 which
 * accompanies this distribution, is reproduced below, and is
 * available at http://www.eclipse.org/org/documents/edl-v10.php
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials provided
 *   with the distribution.
 *
 * - Neither the name of the Eclipse Foundation, Inc. nor the
 *   names of its contributors may be used to endorse or promote
 *   products derived from this software without specific prior
 *   written permission.
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
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 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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package org.eclipse.jgit.util.io;

import java.io.IOException;
import java.io.InterruptedIOException;
import java.io.OutputStream;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicInteger;

import org.eclipse.jgit.internal.JGitText;

OutputStream isolated from interrupts.

Wraps an OutputStream to prevent interrupts during writes from being made
visible to that stream instance. This works around buggy or difficult
OutputStream implementations like JSch that cannot gracefully handle an
interrupt during write.
 Every write (or flush) requires a context switch to another thread. Callers should wrap this stream with BufferedOutputStream using a suitable buffer size to amortize the cost of context switches. 
Since:
4.6/**
 * OutputStream isolated from interrupts.
 * <p>
 * Wraps an OutputStream to prevent interrupts during writes from being made
 * visible to that stream instance. This works around buggy or difficult
 * OutputStream implementations like JSch that cannot gracefully handle an
 * interrupt during write.
 * <p>
 * Every write (or flush) requires a context switch to another thread. Callers
 * should wrap this stream with {@code BufferedOutputStream} using a suitable
 * buffer size to amortize the cost of context switches.
 *
 * @since 4.6
 */
public class IsolatedOutputStream extends OutputStream {
	private final OutputStream dst;
	private final ExecutorService copier;
	private Future<Void> pending;

	
Wraps an OutputStream.
Params:
out – 
           stream to send all writes to./**
	 * Wraps an OutputStream.
	 *
	 * @param out
	 *            stream to send all writes to.
	 */
	public IsolatedOutputStream(OutputStream out) {
		dst = out;
		copier = new ThreadPoolExecutor(1, 1, 0, TimeUnit.MILLISECONDS,
				new ArrayBlockingQueue<>(1), new NamedThreadFactory());
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public void write(int ch) throws IOException {
		write(new byte[] { (byte) ch }, 0, 1);
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public void write(byte[] buf, int pos, int cnt)
			throws IOException {
		checkClosed();
		execute(() -> {
			dst.write(buf, pos, cnt);
			return null;
		});
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public void flush() throws IOException {
		checkClosed();
		execute(() -> {
			dst.flush();
			return null;
		});
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public void close() throws IOException {
		if (!copier.isShutdown()) {
			try {
				if (pending == null || tryCleanClose()) {
					cleanClose();
				} else {
					dirtyClose();
				}
			} finally {
				copier.shutdown();
			}
		}
	}

	private boolean tryCleanClose() {
		/*
		 * If the caller stopped waiting for a prior write or flush, they could
		 * be trying to close a stream that is still in-use. Check if the prior
		 * operation ended in a predictable way.
		 */
		try {
			pending.get(0, TimeUnit.MILLISECONDS);
			pending = null;
			return true;
		} catch (TimeoutException | InterruptedException e) {
			return false;
		} catch (ExecutionException e) {
			pending = null;
			return true;
		}
	}

	private void cleanClose() throws IOException {
		execute(() -> {
			dst.close();
			return null;
		});
	}

	private void dirtyClose() throws IOException {
		/*
		 * Interrupt any still pending write or flush operation. This may cause
		 * massive failures inside of the stream, but its going to be closed as
		 * the next step.
		 */
		pending.cancel(true);

		Future<Void> close;
		try {
			close = copier.submit(() -> {
				dst.close();
				return null;
			});
		} catch (RejectedExecutionException e) {
			throw new IOException(e);
		}
		try {
			close.get(200, TimeUnit.MILLISECONDS);
		} catch (InterruptedException | TimeoutException e) {
			close.cancel(true);
			throw new IOException(e);
		} catch (ExecutionException e) {
			throw new IOException(e.getCause());
		}
	}

	private void checkClosed() throws IOException {
		if (copier.isShutdown()) {
			throw new IOException(JGitText.get().closed);
		}
	}

	private void execute(Callable<Void> task) throws IOException {
		if (pending != null) {
			// Check (and rethrow) any prior failed operation.
			checkedGet(pending);
		}
		try {
			pending = copier.submit(task);
		} catch (RejectedExecutionException e) {
			throw new IOException(e);
		}
		checkedGet(pending);
		pending = null;
	}

	private static void checkedGet(Future<Void> future) throws IOException {
		try {
			future.get();
		} catch (InterruptedException e) {
			throw interrupted(e);
		} catch (ExecutionException e) {
			throw new IOException(e.getCause());
		}
	}

	private static InterruptedIOException interrupted(InterruptedException c) {
		InterruptedIOException e = new InterruptedIOException();
		e.initCause(c);
		return e;
	}

	private static class NamedThreadFactory implements ThreadFactory {
		private static final AtomicInteger cnt = new AtomicInteger();

		@Override
		public Thread newThread(Runnable r) {
			int n = cnt.incrementAndGet();
			String name = IsolatedOutputStream.class.getSimpleName() + '-' + n;
			return new Thread(r, name);
		}
	}
}