/*
 * Copyright (C) 2008-2009, Google Inc.
 * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
 * 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,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * 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,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.eclipse.jgit.util;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;

import org.eclipse.jgit.lib.NullProgressMonitor;
import org.eclipse.jgit.lib.ProgressMonitor;

/**
 * A fully buffered output stream.
 * <p>
 * Subclasses determine the behavior when the in-memory buffer capacity has been
 * exceeded and additional bytes are still being received for output.
 */
public abstract class TemporaryBuffer extends OutputStream {
	/** Default limit for in-core storage. */
	protected static final int DEFAULT_IN_CORE_LIMIT = 1024 * 1024;

	/** Chain of data, if we are still completely in-core; otherwise null. */
	private ArrayList<Block> blocks;

	/**
	 * Maximum number of bytes we will permit storing in memory.
	 * <p>
	 * When this limit is reached the data will be shifted to a file on disk,
	 * preventing the JVM heap from growing out of control.
	 */
	private int inCoreLimit;

	/** If {@link #inCoreLimit} has been reached, remainder goes here. */
	private OutputStream overflow;

	/**
	 * Create a new empty temporary buffer.
	 *
	 * @param limit
	 *            maximum number of bytes to store in memory before entering the
	 *            overflow output path.
	 */
	protected TemporaryBuffer(final int limit) {
		inCoreLimit = limit;
		reset();
	}

	@Override
	public void write(final int b) throws IOException {
		if (overflow != null) {
			overflow.write(b);
			return;
		}

		Block s = last();
		if (s.isFull()) {
			if (reachedInCoreLimit()) {
				overflow.write(b);
				return;
			}

			s = new Block();
			blocks.add(s);
		}
		s.buffer[s.count++] = (byte) b;
	}

	@Override
	public void write(final byte[] b, int off, int len) throws IOException {
		if (overflow == null) {
			while (len > 0) {
				Block s = last();
				if (s.isFull()) {
					if (reachedInCoreLimit())
						break;

					s = new Block();
					blocks.add(s);
				}

				final int n = Math.min(Block.SZ - s.count, len);
				System.arraycopy(b, off, s.buffer, s.count, n);
				s.count += n;
				len -= n;
				off += n;
			}
		}

		if (len > 0)
			overflow.write(b, off, len);
	}

	/**
	 * Copy all bytes remaining on the input stream into this buffer.
	 *
	 * @param in
	 *            the stream to read from, until EOF is reached.
	 * @throws IOException
	 *             an error occurred reading from the input stream, or while
	 *             writing to a local temporary file.
	 */
	public void copy(final InputStream in) throws IOException {
		if (blocks != null) {
			for (;;) {
				Block s = last();
				if (s.isFull()) {
					if (reachedInCoreLimit())
						break;
					s = new Block();
					blocks.add(s);
				}

				final int n = in.read(s.buffer, s.count, Block.SZ - s.count);
				if (n < 1)
					return;
				s.count += n;
			}
		}

		final byte[] tmp = new byte[Block.SZ];
		int n;
		while ((n = in.read(tmp)) > 0)
			overflow.write(tmp, 0, n);
	}

	/**
	 * Obtain the length (in bytes) of the buffer.
	 * <p>
	 * The length is only accurate after {@link #close()} has been invoked.
	 *
	 * @return total length of the buffer, in bytes.
	 */
	public long length() {
		final Block last = last();
		return ((long) blocks.size()) * Block.SZ - (Block.SZ - last.count);
	}

	/**
	 * Convert this buffer's contents into a contiguous byte array.
	 * <p>
	 * The buffer is only complete after {@link #close()} has been invoked.
	 *
	 * @return the complete byte array; length matches {@link #length()}.
	 * @throws IOException
	 *             an error occurred reading from a local temporary file
	 * @throws OutOfMemoryError
	 *             the buffer cannot fit in memory
	 */
	public byte[] toByteArray() throws IOException {
		final long len = length();
		if (Integer.MAX_VALUE < len)
			throw new OutOfMemoryError("Length exceeds maximum array size");
		final byte[] out = new byte[(int) len];
		int outPtr = 0;
		for (final Block b : blocks) {
			System.arraycopy(b.buffer, 0, out, outPtr, b.count);
			outPtr += b.count;
		}
		return out;
	}

	/**
	 * Send this buffer to an output stream.
	 * <p>
	 * This method may only be invoked after {@link #close()} has completed
	 * normally, to ensure all data is completely transferred.
	 *
	 * @param os
	 *            stream to send this buffer's complete content to.
	 * @param pm
	 *            if not null progress updates are sent here. Caller should
	 *            initialize the task and the number of work units to <code>
	 *            {@link #length()}/1024</code>.
	 * @throws IOException
	 *             an error occurred reading from a temporary file on the local
	 *             system, or writing to the output stream.
	 */
	public void writeTo(final OutputStream os, ProgressMonitor pm)
			throws IOException {
		if (pm == null)
			pm = NullProgressMonitor.INSTANCE;
		for (final Block b : blocks) {
			os.write(b.buffer, 0, b.count);
			pm.update(b.count / 1024);
		}
	}

	/** Reset this buffer for reuse, purging all buffered content. */
	public void reset() {
		if (overflow != null) {
			destroy();
		}
		blocks = new ArrayList<Block>(inCoreLimit / Block.SZ);
		blocks.add(new Block());
	}

	/**
	 * Open the overflow output stream, so the remaining output can be stored.
	 *
	 * @return the output stream to receive the buffered content, followed by
	 *         the remaining output.
	 * @throws IOException
	 *             the buffer cannot create the overflow stream.
	 */
	protected abstract OutputStream overflow() throws IOException;

	private Block last() {
		return blocks.get(blocks.size() - 1);
	}

	private boolean reachedInCoreLimit() throws IOException {
		if (blocks.size() * Block.SZ < inCoreLimit)
			return false;

		overflow = overflow();

		final Block last = blocks.remove(blocks.size() - 1);
		for (final Block b : blocks)
			overflow.write(b.buffer, 0, b.count);
		blocks = null;

		overflow = new BufferedOutputStream(overflow, Block.SZ);
		overflow.write(last.buffer, 0, last.count);
		return true;
	}

	public void close() throws IOException {
		if (overflow != null) {
			try {
				overflow.close();
			} finally {
				overflow = null;
			}
		}
	}

	/** Clear this buffer so it has no data, and cannot be used again. */
	public void destroy() {
		blocks = null;

		if (overflow != null) {
			try {
				overflow.close();
			} catch (IOException err) {
				// We shouldn't encounter an error closing the file.
			} finally {
				overflow = null;
			}
		}
	}

	/**
	 * A fully buffered output stream using local disk storage for large data.
	 * <p>
	 * Initially this output stream buffers to memory and is therefore similar
	 * to ByteArrayOutputStream, but it shifts to using an on disk temporary
	 * file if the output gets too large.
	 * <p>
	 * The content of this buffered stream may be sent to another OutputStream
	 * only after this stream has been properly closed by {@link #close()}.
	 */
	public static class LocalFile extends TemporaryBuffer {
		/**
		 * Location of our temporary file if we are on disk; otherwise null.
		 * <p>
		 * If we exceeded the {@link #inCoreLimit} we nulled out {@link #blocks}
		 * and created this file instead. All output goes here through
		 * {@link #overflow}.
		 */
		private File onDiskFile;

		/** Create a new temporary buffer. */
		public LocalFile() {
			this(DEFAULT_IN_CORE_LIMIT);
		}

		/**
		 * Create a new temporary buffer, limiting memory usage.
		 *
		 * @param inCoreLimit
		 *            maximum number of bytes to store in memory. Storage beyond
		 *            this limit will use the local file.
		 */
		public LocalFile(final int inCoreLimit) {
			super(inCoreLimit);
		}

		protected OutputStream overflow() throws IOException {
			onDiskFile = File.createTempFile("jgit_", ".buffer");
			return new FileOutputStream(onDiskFile);
		}

		public long length() {
			if (onDiskFile == null) {
				return super.length();
			}
			return onDiskFile.length();
		}

		public byte[] toByteArray() throws IOException {
			if (onDiskFile == null) {
				return super.toByteArray();
			}

			final long len = length();
			if (Integer.MAX_VALUE < len)
				throw new OutOfMemoryError("Length exceeds maximum array size");
			final byte[] out = new byte[(int) len];
			final FileInputStream in = new FileInputStream(onDiskFile);
			try {
				IO.readFully(in, out, 0, (int) len);
			} finally {
				in.close();
			}
			return out;
		}

		public void writeTo(final OutputStream os, ProgressMonitor pm)
				throws IOException {
			if (onDiskFile == null) {
				super.writeTo(os, pm);
				return;
			}
			if (pm == null)
				pm = NullProgressMonitor.INSTANCE;
			final FileInputStream in = new FileInputStream(onDiskFile);
			try {
				int cnt;
				final byte[] buf = new byte[Block.SZ];
				while ((cnt = in.read(buf)) >= 0) {
					os.write(buf, 0, cnt);
					pm.update(cnt / 1024);
				}
			} finally {
				in.close();
			}
		}

		@Override
		public void destroy() {
			super.destroy();

			if (onDiskFile != null) {
				try {
					if (!onDiskFile.delete())
						onDiskFile.deleteOnExit();
				} finally {
					onDiskFile = null;
				}
			}
		}
	}

	/**
	 * A temporary buffer that will never exceed its in-memory limit.
	 * <p>
	 * If the in-memory limit is reached an IOException is thrown, rather than
	 * attempting to spool to local disk.
	 */
	public static class Heap extends TemporaryBuffer {
		/**
		 * Create a new heap buffer with a maximum storage limit.
		 *
		 * @param limit
		 *            maximum number of bytes that can be stored in this buffer.
		 *            Storing beyond this many will cause an IOException to be
		 *            thrown during write.
		 */
		public Heap(final int limit) {
			super(limit);
		}

		@Override
		protected OutputStream overflow() throws IOException {
			throw new IOException("In-memory buffer limit exceeded");
		}
	}

	static class Block {
		static final int SZ = 8 * 1024;

		final byte[] buffer = new byte[SZ];

		int count;

		boolean isFull() {
			return count == SZ;
		}
	}
}