/**

  * Copyright 2009 Martin Vysny.

  *

  * This file is part of WebVM.

  *

  * WebVM is free software: you can redistribute it and/or modify

  * it under the terms of the GNU General Public License as published by

  * the Free Software Foundation, either version 3 of the License, or

  * (at your option) any later version.

  *

  * WebVM 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 for more details.

  *

  * You should have received a copy of the GNU General Public License

  * along with WebVM.  If not, see <http://www.gnu.org/licenses/>.

  */

 package sk.baka.webvm.misc;

 import java.util.ArrayList;

 import java.util.List;

 import java.util.Queue;

 import java.util.concurrent.ConcurrentLinkedQueue;

 /**

  * A simple object that holds a fixed-size history. A fixed-size FIFO implementation.

  * @param <T> type of items contained in this history object.

  * @author Martin Vysny

  */

 public final class SimpleFixedSizeFIFO<T> {

     private final int maxLength;

     private int historyLength = 0;

     private final Queue<T> history = new ConcurrentLinkedQueue<T>();

     /**

      * Creates new instance.

      * @param maxLength maximum length of the FIFO queue. Old items are dropped automatically.

      */

     public SimpleFixedSizeFIFO(final int maxLength) {

         super();

         this.maxLength = maxLength;

     }

     /**

      * Adds an item to the history, discarding oldest items when the maximum length has been reached. Not thread-safe - may be called from one thread instance only.

      * @param item the item to add

      */

     public void add(T item) {

         while (historyLength >= maxLength) {

             history.poll();

             historyLength--;

         }

         history.add(item);

         historyLength++;

         newest = item;

     }

     /**

      * Returns a snapshot of the FIFO. Thread-safe.

      * @return a snapshot, first item is the oldest one.

      */

     public List<T> toList() {

         return new ArrayList<T>(history);

     }

     /**

      * Clears the history.

      */

     public void clear() {

         history.clear();

         newest = null;

     }

     private T newest = null;

     /**

      * Returns the newest item put into this queue. Not thread-safe - may be called from the same thread which is {@link #add(java.lang.Object) adding} items only.

      * @return newest item or null if the FIFO is empty.

      */

     public T getNewest() {

         return newest;

     }

 }