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	/*
	* Copyright (c) 2000, 2003, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package javax.imageio.stream;

	import java.util.ArrayList;
	import java.io.InputStream;
	import java.io.OutputStream;
	import java.io.IOException;

	/**
	* Package-visible class consolidating common code for
	* <code>MemoryCacheImageInputStream</code> and
	* <code>MemoryCacheImageOutputStream</code>.
	* This class keeps an <code>ArrayList</code> of 8K blocks,
	* loaded sequentially. Blocks may only be disposed of
	* from the index 0 forward. As blocks are freed, the
	* corresponding entries in the array list are set to
	* <code>null</code>, but no compacting is performed.
	* This allows the index for each block to never change,
	* and the length of the cache is always the same as the
	* total amount of data ever cached. Cached data is
	* therefore always contiguous from the point of last
	* disposal to the current length.
	*
	* <p> The total number of blocks resident in the cache must not
	* exceed <code>Integer.MAX_VALUE</code>. In practice, the limit of
	* available memory will be exceeded long before this becomes an
	* issue, since a full cache would contain 8192*2^31 = 16 terabytes of
	* data.
	*
	* A <code>MemoryCache</code> may be reused after a call
	* to <code>reset()</code>.
	*/
	class MemoryCache {

	private static final int BUFFER_LENGTH = 8192;

	private ArrayList cache = new ArrayList();

	private long cacheStart = 0L;

	/**
	* The largest position ever written to the cache.
	*/
	private long length = 0L;

	private byte[] getCacheBlock(long blockNum) throws IOException {
	long blockOffset = blockNum - cacheStart;
	if (blockOffset > Integer.MAX_VALUE) {
	// This can only happen when the cache hits 16 terabytes of
	// contiguous data...
	throw new IOException("Cache addressing limit exceeded!");
	}
	return (byte[])cache.get((int)blockOffset);
	}

	/**
	* Ensures that at least <code>pos</code> bytes are cached,
	* or the end of the source is reached. The return value
	* is equal to the smaller of <code>pos</code> and the
	* length of the source.
	*/
	public long loadFromStream(InputStream stream, long pos)
	throws IOException {
	// We've already got enough data cached
	if (pos < length) {
	return pos;
	}

	int offset = (int)(length % BUFFER_LENGTH);
	byte [] buf = null;

	long len = pos - length;
	if (offset != 0) {
	buf = getCacheBlock(length/BUFFER_LENGTH);
	}

	while (len > 0) {
	if (buf == null) {
	try {
	buf = new byte[BUFFER_LENGTH];
	} catch (OutOfMemoryError e) {
	throw new IOException("No memory left for cache!");
	}
	offset = 0;
	}

	int left = BUFFER_LENGTH - offset;
	int nbytes = (int)Math.min(len, (long)left);
	nbytes = stream.read(buf, offset, nbytes);
	if (nbytes == -1) {
	return length; // EOF
	}

	if (offset == 0) {
	cache.add(buf);
	}

	len -= nbytes;
	length += nbytes;
	offset += nbytes;

	if (offset >= BUFFER_LENGTH) {
	// we've filled the current buffer, so a new one will be
	// allocated next time around (and offset will be reset to 0)
	buf = null;
	}
	}

	return pos;
	}

	/**
	* Writes out a portion of the cache to an <code>OutputStream</code>.
	* This method preserves no state about the output stream, and does
	* not dispose of any blocks containing bytes written. To dispose
	* blocks, use {@link #disposeBefore <code>disposeBefore()</code>}.
	*
	* @exception IndexOutOfBoundsException if any portion of
	* the requested data is not in the cache (including if <code>pos</code>
	* is in a block already disposed), or if either <code>pos</code> or
	* <code>len</code> is < 0.
	*/
	public void writeToStream(OutputStream stream, long pos, long len)
	throws IOException {
	if (pos + len > length) {
	throw new IndexOutOfBoundsException("Argument out of cache");
	}
	if ((pos < 0) \|\| (len < 0)) {
	throw new IndexOutOfBoundsException("Negative pos or len");
	}
	if (len == 0) {
	return;
	}

	long bufIndex = pos/BUFFER_LENGTH;
	if (bufIndex < cacheStart) {
	throw new IndexOutOfBoundsException("pos already disposed");
	}
	int offset = (int)(pos % BUFFER_LENGTH);

	byte[] buf = getCacheBlock(bufIndex++);
	while (len > 0) {
	if (buf == null) {
	buf = getCacheBlock(bufIndex++);
	offset = 0;
	}
	int nbytes = (int)Math.min(len, (long)(BUFFER_LENGTH - offset));
	stream.write(buf, offset, nbytes);
	buf = null;
	len -= nbytes;
	}
	}

	/**
	* Ensure that there is space to write a byte at the given position.
	*/
	private void pad(long pos) throws IOException {
	long currIndex = cacheStart + cache.size() - 1;
	long lastIndex = pos/BUFFER_LENGTH;
	long numNewBuffers = lastIndex - currIndex;
	for (long i = 0; i < numNewBuffers; i++) {
	try {
	cache.add(new byte[BUFFER_LENGTH]);
	} catch (OutOfMemoryError e) {
	throw new IOException("No memory left for cache!");
	}
	}
	}

	/**
	* Overwrites and/or appends the cache from a byte array.
	* The length of the cache will be extended as needed to hold
	* the incoming data.
	*
	* @param b an array of bytes containing data to be written.
	* @param off the starting offset withing the data array.
	* @param len the number of bytes to be written.
	* @param pos the cache position at which to begin writing.
	*
	* @exception NullPointerException if <code>b</code> is <code>null</code>.
	* @exception IndexOutOfBoundsException if <code>off</code>,
	* <code>len</code>, or <code>pos</code> are negative,
	* or if <code>off+len > b.length</code>.
	*/
	public void write(byte[] b, int off, int len, long pos)
	throws IOException {
	if (b == null) {
	throw new NullPointerException("b == null!");
	}
	// Fix 4430357 - if off + len < 0, overflow occurred
	if ((off < 0) \|\| (len < 0) \|\| (pos < 0) \|\|
	(off + len > b.length) \|\| (off + len < 0)) {
	throw new IndexOutOfBoundsException();
	}

	// Ensure there is space for the incoming data
	long lastPos = pos + len - 1;
	if (lastPos >= length) {
	pad(lastPos);
	length = lastPos + 1;
	}

	// Copy the data into the cache, block by block
	int offset = (int)(pos % BUFFER_LENGTH);
	while (len > 0) {
	byte[] buf = getCacheBlock(pos/BUFFER_LENGTH);
	int nbytes = Math.min(len, BUFFER_LENGTH - offset);
	System.arraycopy(b, off, buf, offset, nbytes);

	pos += nbytes;
	off += nbytes;
	len -= nbytes;
	offset = 0; // Always after the first time
	}
	}

	/**
	* Overwrites or appends a single byte to the cache.
	* The length of the cache will be extended as needed to hold
	* the incoming data.
	*
	* @param b an <code>int</code> whose 8 least significant bits
	* will be written.
	* @param pos the cache position at which to begin writing.
	*
	* @exception IndexOutOfBoundsException if <code>pos</code> is negative.
	*/
	public void write(int b, long pos) throws IOException {
	if (pos < 0) {
	throw new ArrayIndexOutOfBoundsException("pos < 0");
	}

	// Ensure there is space for the incoming data
	if (pos >= length) {
	pad(pos);
	length = pos + 1;
	}

	// Insert the data.
	byte[] buf = getCacheBlock(pos/BUFFER_LENGTH);
	int offset = (int)(pos % BUFFER_LENGTH);
	buf[offset] = (byte)b;
	}

	/**
	* Returns the total length of data that has been cached,
	* regardless of whether any early blocks have been disposed.
	* This value will only ever increase.
	*/
	public long getLength() {
	return length;
	}

	/**
	* Returns the single byte at the given position, as an
	* <code>int</code>. Returns -1 if this position has
	* not been cached or has been disposed.
	*/
	public int read(long pos) throws IOException {
	if (pos >= length) {
	return -1;
	}

	byte[] buf = getCacheBlock(pos/BUFFER_LENGTH);
	if (buf == null) {
	return -1;
	}

	return buf[(int)(pos % BUFFER_LENGTH)] & 0xff;
	}

	/**
	* Copy <code>len</code> bytes from the cache, starting
	* at cache position <code>pos</code>, into the array
	* <code>b</code> at offset <code>off</code>.
	*
	* @exception NullPointerException if b is <code>null</code>
	* @exception IndexOutOfBoundsException if <code>off</code>,
	* <code>len</code> or <code>pos</code> are negative or if
	* <code>off + len > b.length</code> or if any portion of the
	* requested data is not in the cache (including if
	* <code>pos</code> is in a block that has already been disposed).
	*/
	public void read(byte[] b, int off, int len, long pos)
	throws IOException {
	if (b == null) {
	throw new NullPointerException("b == null!");
	}
	// Fix 4430357 - if off + len < 0, overflow occurred
	if ((off < 0) \|\| (len < 0) \|\| (pos < 0) \|\|
	(off + len > b.length) \|\| (off + len < 0)) {
	throw new IndexOutOfBoundsException();
	}
	if (pos + len > length) {
	throw new IndexOutOfBoundsException();
	}

	long index = pos/BUFFER_LENGTH;
	int offset = (int)pos % BUFFER_LENGTH;
	while (len > 0) {
	int nbytes = Math.min(len, BUFFER_LENGTH - offset);
	byte[] buf = getCacheBlock(index++);
	System.arraycopy(buf, offset, b, off, nbytes);

	len -= nbytes;
	off += nbytes;
	offset = 0; // Always after the first time
	}
	}

	/**
	* Free the blocks up to the position <code>pos</code>.
	* The byte at <code>pos</code> remains available.
	*
	* @exception IndexOutOfBoundsException if <code>pos</code>
	* is in a block that has already been disposed.
	*/
	public void disposeBefore(long pos) {
	long index = pos/BUFFER_LENGTH;
	if (index < cacheStart) {
	throw new IndexOutOfBoundsException("pos already disposed");
	}
	long numBlocks = Math.min(index - cacheStart, cache.size());
	for (long i = 0; i < numBlocks; i++) {
	cache.remove(0);
	}
	this.cacheStart = index;
	}

	/**
	* Erase the entire cache contents and reset the length to 0.
	* The cache object may subsequently be reused as though it had just
	* been allocated.
	*/
	public void reset() {
	cache.clear();
	cacheStart = 0;
	length = 0L;
	}
	}

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