/*

 * Copyright (c) 2018, 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 jdk.nio.zipfs;

import java.io.IOException;

import java.nio.ByteBuffer;

import java.nio.channels.ClosedChannelException;

import java.nio.channels.NonWritableChannelException;

import java.nio.channels.SeekableByteChannel;

import java.util.Arrays;

import java.util.concurrent.locks.ReadWriteLock;

import java.util.concurrent.locks.ReentrantReadWriteLock;

public class ByteArrayChannel implements SeekableByteChannel {

    private final ReadWriteLock rwlock = new ReentrantReadWriteLock();

    private byte buf[];

    /*

     * The current position of this channel.

     */

    private int pos;

    /*

     * The index that is one greater than the last valid byte in the channel.

     */

    private int last;

    private boolean closed;

    private boolean readonly;

    /*

     * Creates a {@code ByteArrayChannel} with size {@code sz}.

     */

    ByteArrayChannel(int sz, boolean readonly) {

        this.buf = new byte[sz];

        this.pos = this.last = 0;

        this.readonly = readonly;

    }

    /*

     * Creates a ByteArrayChannel with its 'pos' at 0 and its 'last' at buf's end.

     * Note: no defensive copy of the 'buf', used directly.

     */

    ByteArrayChannel(byte[] buf, boolean readonly) {

        this.buf = buf;

        this.pos = 0;

        this.last = buf.length;

        this.readonly = readonly;

    }

    @Override

    public boolean isOpen() {

        return !closed;

    }

    @Override

    public long position() throws IOException {

        beginRead();

        try {

            ensureOpen();

            return pos;

        } finally {

            endRead();

        }

    }

    @Override

    public SeekableByteChannel position(long pos) throws IOException {

        beginWrite();

        try {

            ensureOpen();

            if (pos < 0 || pos >= Integer.MAX_VALUE)

                throw new IllegalArgumentException("Illegal position " + pos);

            this.pos = Math.min((int)pos, last);

            return this;

        } finally {

            endWrite();

        }

    }

    @Override

    public int read(ByteBuffer dst) throws IOException {

        beginWrite();

        try {

            ensureOpen();

            if (pos == last)

                return -1;

            int n = Math.min(dst.remaining(), last - pos);

            dst.put(buf, pos, n);

            pos += n;

            return n;

        } finally {

            endWrite();

        }

    }

    @Override

    public SeekableByteChannel truncate(long size) throws IOException {

        if (readonly)

            throw new NonWritableChannelException();

        ensureOpen();

        throw new UnsupportedOperationException();

    }

    @Override

    public int write(ByteBuffer src) throws IOException {

        if (readonly)

            throw new NonWritableChannelException();

        beginWrite();

        try {

            ensureOpen();

            int n = src.remaining();

            ensureCapacity(pos + n);

            src.get(buf, pos, n);

            pos += n;

            if (pos > last) {

                last = pos;

            }

            return n;

        } finally {

            endWrite();

        }

    }

    @Override

    public long size() throws IOException {

        beginRead();

        try {

            ensureOpen();

            return last;

        } finally {

            endRead();

        }

    }

    @Override

    public void close() throws IOException {

        if (closed)

            return;

        beginWrite();

        try {

            closed = true;

            buf = null;

            pos = 0;

            last = 0;

        } finally {

            endWrite();

        }

    }

    /**

     * Creates a newly allocated byte array. Its size is the current

     * size of this channel and the valid contents of the buffer

     * have been copied into it.

     *

     * @return the current contents of this channel, as a byte array.

     */

    public byte[] toByteArray() {

        beginRead();

        try {

            // avoid copy if last == bytes.length?

            return Arrays.copyOf(buf, last);

        } finally {

            endRead();

        }

    }

    private void ensureOpen() throws IOException {

        if (closed)

            throw new ClosedChannelException();

    }

    private final void beginWrite() {

        rwlock.writeLock().lock();

    }

    private final void endWrite() {

        rwlock.writeLock().unlock();

    }

    private final void beginRead() {

        rwlock.readLock().lock();

    }

    private final void endRead() {

        rwlock.readLock().unlock();

    }

    private void ensureCapacity(int minCapacity) {

        // overflow-conscious code

        if (minCapacity - buf.length > 0) {

            grow(minCapacity);

        }

    }

    /**

     * The maximum size of array to allocate.

     * Some VMs reserve some header words in an array.

     * Attempts to allocate larger arrays may result in

     * OutOfMemoryError: Requested array size exceeds VM limit

     */

    private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;

    /**

     * Increases the capacity to ensure that it can hold at least the

     * number of elements specified by the minimum capacity argument.

     *

     * @param minCapacity the desired minimum capacity

     */

    private void grow(int minCapacity) {

        // overflow-conscious code

        int oldCapacity = buf.length;

        int newCapacity = oldCapacity << 1;

        if (newCapacity - minCapacity < 0)

            newCapacity = minCapacity;

        if (newCapacity - MAX_ARRAY_SIZE > 0)

            newCapacity = hugeCapacity(minCapacity);

        buf = Arrays.copyOf(buf, newCapacity);

    }

    private static int hugeCapacity(int minCapacity) {

        if (minCapacity < 0) // overflow

            throw new OutOfMemoryError();

        return (minCapacity > MAX_ARRAY_SIZE) ?

            Integer.MAX_VALUE :

            MAX_ARRAY_SIZE;

    }

}