/*
 * StreamBufferList.java -  Maintain a list of StreamBuffer objects.
 *
 * Copyright (c) 1996 Chuck McManis, All Rights Reserved.
 *
 * Permission to use, copy, modify, and distribute this software
 * and its documentation for NON-COMMERCIAL purposes and without
 * fee is hereby granted provided that this copyright notice
 * appears in all copies.
 *
 * CHUCK MCMANIS MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE
 * SUITABILITY OF THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING
 * BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT. CHUCK MCMANIS
 * SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT
 * OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
 */

package util.comm;

/**
 * This class is private to the util.comm package and maintains a list
 * of StreamBuffer objects for its client. Both the DataChannelInputStream
 * and the DataChannelOutputStram classes use these lists to keep active
 * and free lists of stream buffers.
 */
class StreamBufferList {

    StreamBuffer        buf;
    StreamBufferList    next;

    private StreamBufferList lastValid;
    private StreamBufferList lastInChain;

    public StreamBufferList(StreamBuffer z) {
        buf = z;
        next = null;
    }


    public StreamBufferList() {
        buf = null; next = null; lastValid = null; lastInChain = null;
    }

    synchronized StreamBuffer getBuffer() {

        // if the list is empty then return null.
        if (next == null)
            return null;

        StreamBuffer result = next.buf;
        next.buf = null; // clear it out.

        /*
         * Case 1: There is only one valid buffer.
         */
        if (lastValid == next) {
            lastValid = null;
            return result;
        }


        /*
         * Case 2: There is more than one valid buffer in the chain.
         */
        lastInChain.next = next;
        lastInChain = next;

        next = next.next;
        lastInChain.next = null;
        return result;
    }

    synchronized void putBuffer(StreamBuffer z) {
        // Case 0: The list is empty.
        if (next == null) {
            next = new StreamBufferList(z);
            lastValid = next;
            lastInChain = next;
            return;
        }

        // Case 1: The list is non-empty, but there is a left over list item.
        if (lastValid == null) {
            lastValid = next;
            next.buf = z;
            return;
        }

        // case 1b.
        if (lastValid.next != null) {
            lastValid.next.buf = z;
            lastValid = lastValid.next;
            return;
        }

        // Case 2: grow the list.
        lastValid.next = new StreamBufferList(z);
        lastInChain = lastValid.next;
        lastValid = lastValid.next;
    }

    /**
     * Return the total number of bytes queued in this streambuffer list.
     */
    public synchronized int avail() {
        int total = 0;

        for (StreamBufferList q = next; (q != null) && (q.buf != null); q = q.next)
            total += q.buf.avail();
        return total;
    }

}