narya/src/as/com/threerings/util/RingBuffer.as

//
// $Id$
//
// Narya library - tools for developing networked games
// Copyright (C) 2002-2007 Three Rings Design, Inc., All Rights Reserved
// http://www.threerings.net/code/narya/
//
// 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 com.threerings.util {

public class RingBuffer
{
    /** Creates a new RingBuffer with the specified capacity. */
    public function RingBuffer (capacity :uint = 1)
    {
        _capacity = capacity;
        _array.length = _capacity;
    }

    /** Returns the capacity of the RingBuffer. */
    public function get capacity () :uint
    {
        return _capacity;
    }

    /**
     * Sets the capacity of the RingBuffer.
     * If the new capacity is less than the RingBuffer's length,
     * elements will be removed from the end of the RingBuffer
     * to accommodate the smaller capacity.
     */
    public function set capacity (newCapacity :uint) :void
    {
        // Copy all the elements to a new array.
        var newArray :Array = new Array();
        var newLength :uint = Math.min(_length, newCapacity);
        newArray.length = newCapacity;
        for (var i :uint = 0; i < newLength; ++i) {
            newArray[i] = this.at(i);
        }

        _capacity = newCapacity;
        _length = newLength;
        _array = newArray;
        _firstIndex = 0;
    }

    /** Returns the number of elements currently stored in the RingBuffer. */
    public function get length () :uint
    {
        return _length;
    }

    /** Returns true if the RingBuffer contains 0 elements. */
    public function get empty () :Boolean
    {
        return (0 == _length);
    }

    /**
     * Adds the specified elements to the front of the RingBuffer.
     * If the RingBuffer's length is equal to its capacity, this
     * will cause elements to be removed from the back of
     * the RingBuffer.
     * Returns the new length of the RingBuffer.
     */
    public function unshift (...args) :uint
    {
        for (var i :int = args.length - 1; i >= 0; --i) {
            var index :uint = (_firstIndex > 0 ? _firstIndex - 1 : _capacity - 1);
            _array[index] = args[i];
            _length = Math.min(_length + 1, _capacity);
            _firstIndex = index;
        }

        return _length;
    }

    /**
     * Adds the specified elements to the back of the RingBuffer.
     * If the RingBuffer's length is equal to its capacity, this
     * will cause a elements to be removed from the front of
     * the RingBuffer.
     * Returns the new length of the RingBuffer.
     */
    public function push (...args) :uint
    {
        for (var i :uint = 0; i < args.length; ++i) {
            var index :uint = ((_firstIndex + _length) % _capacity);
            _array[index] = args[i];
            _length = Math.min(_length + 1, _capacity);

            // did we overwrite the first index?
            if (index == _firstIndex && _length == _capacity) {
                _firstIndex = (_firstIndex < _capacity - 1 ? _firstIndex + 1 : 0);
            }
        }

        return _length;
    }

    /**
     * Removes the first element from the RingBuffer and returns it.
     * If the RingBuffer is empty, shift() will return undefined.
     */
    public function shift () :*
    {
        if (this.empty) {
            return undefined;
        }

        var obj :* = _array[_firstIndex];
        _array[_firstIndex] = undefined;
        _firstIndex = (_firstIndex < _capacity - 1 ? _firstIndex + 1 : 0);
        --_length;

        return obj;
    }

    /**
     * Removes the last element from the RingBuffer and returns it.
     * If the RingBuffer is empty, pop() will return undefined.
     */
    public function pop () :*
    {
        if (this.empty) {
            return undefined;
        }

        var lastIndex :uint = ((_firstIndex + _length - 1) % _capacity);

        var obj :* = _array[lastIndex];
        _array[lastIndex] = undefined;
        --_length;

        return obj;
    }

    /** Removes all elements from the RingBuffer. */
    public function clear () :void
    {
        _array = new Array();
        _array.length = _capacity;
        _length = 0;
        _firstIndex = 0;
    }

    /**
     * Returns the element at the specified index.
     * If index >= length, at() will return undefined.
     */
    public function at (index :uint) :*
    {
        if (index >= _length) {
            return undefined;
        } else {
            var index :uint = ((_firstIndex + index) % _capacity);
            return _array[index];
        }
    }
    
    /**
     * Executes a test function on each item in the ring buffer
     * until an item is reached that returns false for the specified
     * function.
     * 
     * Returns a Boolean value of true if all items in the buffer return
     * true for the specified function; otherwise, false.
     */
    public function every (callback :Function, thisObject :* = null) :Boolean
    {
        for (var i :int = 0; i < _length; ++i) {
            if (!callback.call(thisObject, this.at(i))) {
                return false;
            }
        }
        
        return true;
    }
    
    /**
     * Executes a function on each item in the ring buffer.
     */ 
    public function forEach (callback :Function, thisObject :* = null) :void
    {
        for (var i :int = 0; i < _length; ++i) {
            callback.call(thisObject, this.at(i));
        }
    }
    
    /**
     * Searches for an item in the ring buffer by using strict equality
     * (===) and returns the index position of the item, or -1
     * if the item is not found.
     */
    public function indexOf (searchElement :*, fromIndex :int = 0) :int
    {
        for (var i :int = 0; i < _length; ++i) {
            if (this.at(i) === searchElement) {
                return i;
            }
        }
        
        return -1;
    }

    protected var _array :Array = new Array();
    protected var _capacity :uint;
    protected var _length :uint;
    protected var _firstIndex :uint;
}

}