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Core components to access jclouds services
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/*
 * 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.jclouds.collect;

import java.util.Iterator;

import com.google.common.annotations.Beta;
import com.google.common.collect.FluentIterable;
import com.google.common.collect.Iterators;
import com.google.common.collect.UnmodifiableIterator;

/**
 * Extends {@link FluentIterable} allowing you to lazily advance through
 * sequence of pages in a result set. Typically used in APIs that return only a
 * certain number of records at a time.
 * 
 * Simplest usage is to employ the {@link #concat} convenience function, and iterate.
 * 
 *  * FluentIterable images = imageApi.listInDetail().concat();
 *
 * for (Image image: images) {
 *    System.out.println(image);
 * }
 * 
 *  
 * Another usage is to employ the {@link #concat} convenience function, and one
 * of the methods from {@link FluentIterable}.
 * 
 *  *    Optional image = imageApi.listInDetail().concat().firstMatch(isInterestingImage());
 *    System.out.println(image.orNull());
 * ...
 * private static Predicate isInterestingImage() {
 *    return new Predicate() {
 *       {@literal @}Override
 *       public boolean apply(Image image) {
 *          return image.getName().startsWith("Arch");
 *       }
 *    };
 * }
 * 
 */
@Beta
public abstract class PagedIterable extends FluentIterable> {

   /**
    * Combines all the pages into a single unmodifiable iterable. ex.
    * 
    *     * FluentIterable blobs = blobstore.list(...).concat();
    * for (StorageMetadata blob : blobs) {
    *     process(blob);
    * }
    * 
    * 
    * @see Iterators#concat
    */
   public FluentIterable concat() {
      final Iterator> iterator = iterator();
      final UnmodifiableIterator> unmodifiable = new UnmodifiableIterator>() {
         @Override
         public boolean hasNext() {
            return iterator.hasNext();
         }

         @Override
         public Iterator next() {
            return iterator.next().iterator();
         }
      };
      return new FluentIterable() {
         @Override
         public Iterator iterator() {
            return Iterators.concat(unmodifiable);
         }
      };
   }

}