/* Soot - a J*va Optimization Framework
 * Copyright (C) 2007 Manu Sridharan
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */
package soot.jimple.spark.ondemand.genericutil;

/**
 * A FIFO queue of objects, implemented as a
 * circular buffer.  NOTE: elements stored in the
 * buffer should be non-null; this is not checked
 * for performance reasons.
 * 
 * @author Manu Sridharan
 */
public final class FIFOQueue {

    /**
     * the buffer.
     */
    private Object[] _buf;

    /**
     * pointer to current top of buffer
     */
    private int _top;

    /**
     * point to current bottom of buffer, where
     * things will be added
     * invariant: after call to add / remove,
     * should always point to an empty slot in
     * the buffer
     */
    private int _bottom;

    /**
     * @param initialSize_ the initial size of the queue
     */
    public FIFOQueue(int initialSize_) {
        _buf = new Object[initialSize_];
    }

    public FIFOQueue() {
        this(10);
    }

    public boolean push(Object obj_) {
        return add(obj_);
    }
    /**
     * add an element to the bottom of the queue
     */
    public boolean add(Object obj_) {
        //        Assert.chk(obj_ != null);
        // add the element
        _buf[_bottom] = obj_;
        // increment bottom, wrapping around if necessary
        _bottom = (_bottom == _buf.length - 1) ? 0 : _bottom + 1;
        // see if we need to increase the queue size
        if (_bottom == _top) {
            // allocate a new array and copy
            int oldLen = _buf.length;
            int newLen = oldLen * 2;
            //            System.out.println("growing buffer to size " + newLen);
            Object[] newBuf = new Object[newLen];
            int topToEnd = oldLen - _top;
            int newTop = newLen - topToEnd;
            // copy from 0 to _top to beginning of new buffer,
            // _top to _buf.length to the end of the new buffer
            System.arraycopy(_buf, 0, newBuf, 0, _top);
            System.arraycopy(_buf, _top, newBuf, newTop, topToEnd);
            _buf = newBuf;
            _top = newTop;
            return true;
        }
        return false;
    }

    public Object pop() {
        return remove();
    }
    
    /**
     * remove the top element from the buffer
     */
    public Object remove() {
        // check if buffer is empty
        if (_bottom == _top) return null;
        Object ret = _buf[_top];
        // increment top, wrapping if necessary
        _top = (_top == _buf.length - 1) ? 0 : _top + 1;
        return ret;
    }

    public boolean isEmpty() {
        return _bottom == _top;
    }

    public String toString() {
        return _bottom + " " + _top;
    }
    
    public void clear() {
    	_bottom = 0;
    	_top = 0;
    }
}