/*

  * Licensed to the Apache Software Foundation (ASF) under one or more

  * contributor license agreements.  See the NOTICE file distributed with

  * this work for additional information regarding copyright ownership.

  * The ASF licenses this file to You under the Apache License, Version 2.0

  * (the "License"); you may not use this file except in compliance with

  * the License.  You may obtain a copy of the License at

  *

  *     http://www.apache.org/licenses/LICENSE-2.0

  *

  * Unless required by applicable law or agreed to in writing, software

  * distributed under the License is distributed on an "AS IS" BASIS,

  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

  * See the License for the specific language governing permissions and

  * limitations under the License.

  */

 package org.apache.commons.configuration;

 import java.util.Iterator;

 import java.util.NoSuchElementException;

 /**

  * * A specialized iterator implementation used by {@link AbstractConfiguration}

  * to return an iteration over all keys starting with a specified prefix.

  *

  * <p>This class is basically a stripped-down version of the

  * {@code FilterIterator} class of Commons Collections</p>

  *

  * @author <a href="http://commons.apache.org/configuration/team-list.html">Commons Configuration team</a>

  * @version $Id: PrefixedKeysIterator.java 1205603 2011-11-23 21:17:38Z oheger $

  */

 class PrefixedKeysIterator implements Iterator<String>

 {

     /** Stores the wrapped iterator. */

     private final Iterator<String> iterator;

     /** Stores the prefix. */

     private final String prefix;

     /** Stores the next element in the iteration. */

     private String nextElement;

     /** A flag whether the next element has been calculated. */

     private boolean nextElementSet;

     /**

      * Creates a new instance of {@code PrefixedKeysIterator} and sets

      * the wrapped iterator and the prefix for the accepted keys.

      *

      * @param wrappedIterator the wrapped iterator

      * @param keyPrefix the prefix of the allowed keys

      */

     public PrefixedKeysIterator(Iterator<String> wrappedIterator, String keyPrefix)

     {

         iterator = wrappedIterator;

         prefix = keyPrefix;

     }

     /**

      * Returns a flag whether there are more elements in the iteration.

      *

      * @return a flag if there is a next element

      */

     public boolean hasNext()

     {

         return nextElementSet || setNextElement();

     }

     /**

      * Returns the next element in the iteration. This is the next key that

      * matches the specified prefix.

      *

      * @return the next element in the iteration

      * @throws NoSuchElementException if there is no next element

      */

     public String next()

     {

         if (!nextElementSet && !setNextElement())

         {

             throw new NoSuchElementException();

         }

         nextElementSet = false;

         return nextElement;

     }

     /**

      * Removes from the underlying collection of the base iterator the last

      * element returned by this iterator. This method can only be called if

      * {@code next()} was called, but not after {@code hasNext()},

      * because the {@code hasNext()} call changes the base iterator.

      *

      * @throws IllegalStateException if {@code hasNext()} has already

      *         been called.

      */

     public void remove()

     {

         if (nextElementSet)

         {

             throw new IllegalStateException("remove() cannot be called");

         }

         iterator.remove();

     }

     /**

      * Determines the next element in the iteration. The return value indicates

      * whether such an element can be found.

      *

      * @return a flag whether a next element exists

      */

     private boolean setNextElement()

     {

         while (iterator.hasNext())

         {

             String key = iterator.next();

             if (key.startsWith(prefix + ".") || key.equals(prefix))

             {

                 nextElement = key;

                 nextElementSet = true;

                 return true;

             }

         }

         return false;

     }

 }