/*
    * 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.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
   * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
   * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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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.
   * <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.
  	 *
  	 * @param out
  	 *            stream to send all writes to.
  	 */
  	public IsolatedOutputStream(OutputStream out) {
  		dst = out;
  		copier = new ThreadPoolExecutor(1, 1, 0, TimeUnit.MILLISECONDS,
  				new ArrayBlockingQueue<Runnable>(1), new NamedThreadFactory());
  	}
  
  	@Override
  	public void write(int ch) throws IOException {
  		write(new byte[] { (byte) ch }, 0, 1);
  	}
  
  	@Override
 	public void write(final byte[] buf, final int pos, final int cnt)
 			throws IOException {
 		checkClosed();
 		execute(new Callable<Void>() {
 			@Override
 			public Void call() throws IOException {
 				dst.write(buf, pos, cnt);
 				return null;
 			}
 		});
 	}
 
 	@Override
 	public void flush() throws IOException {
 		checkClosed();
 		execute(new Callable<Void>() {
 			@Override
 			public Void call() throws IOException {
 				dst.flush();
 				return null;
 			}
 		});
 	}
 
 	@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(new Callable<Void>() {
 			@Override
 			public Void call() throws IOException {
 				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(new Callable<Void>() {
 				@Override
 				public Void call() throws IOException {
 					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);
 		}
 	}
 }