/*

 * 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<byte[]> 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 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 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;

    }

 }