/**

  * Copyright (c) 2012-2015, jcabi.com

  * All rights reserved.

  *

  * Redistribution and use in source and binary forms, with or without

  * modification, are permitted provided that the following conditions

  * are met: 1) Redistributions of source code must retain the above

  * copyright notice, this list of conditions and the following

  * disclaimer. 2) Redistributions in binary form must reproduce the above

  * copyright notice, this list of conditions and the following

  * disclaimer in the documentation and/or other materials provided

  * with the distribution. 3) Neither the name of the jcabi.com nor

  * the names of its contributors may be used to endorse or promote

  * products derived from this software without specific prior written

  * permission.

  *

  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT

  * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND

  * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL

  * THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,

  * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES

  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR

  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,

  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)

  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED

  * OF THE POSSIBILITY OF SUCH DAMAGE.

  */

 package com.jcabi.s3;

 import com.amazonaws.AmazonServiceException;

 import com.amazonaws.services.s3.AmazonS3;

 import com.amazonaws.services.s3.model.ListObjectsRequest;

 import com.amazonaws.services.s3.model.ObjectListing;

 import com.amazonaws.services.s3.model.S3ObjectSummary;

 import com.jcabi.log.Logger;

 import java.util.Iterator;

 import java.util.LinkedList;

 import java.util.List;

 import java.util.NoSuchElementException;

 /**

  * Iterator for large lists returned by S3.

  * @author Roman Kisilenko (roman.kisilenko@gmail.com)

  * @version $Id: 438e29b243c8fac5b3971a89e2a13a83fd557d9d $

  * @since 0.10

  */

 class AwsListIterator implements Iterator<String> {

     /**

      * Region we're in.

      */

     private final transient Region region;

     /**

      * Bucket name.

      */

     private final transient String bucket;

     /**

      * Prefix to use.

      */

     private final transient String prefix;

     /**

      * Partial S3 response iterator.

      */

     private transient List<String> partial;

     /**

      * Next marker for partial response or null if response contains no more

      * data.

      */

     private transient String marker;

     /**

      * Constructs AwsListIterator.

      * @param pfx Key prefix

      * @param rgn Region we're in

      * @param bkt Bucket name

      */

     AwsListIterator(final Region rgn, final String bkt,

         final String pfx) {

         this.prefix = pfx;

         this.region = rgn;

         this.bucket = bkt;

     }

     @Override

     public final boolean hasNext() {

         if (this.partial == null || this.partial.isEmpty()

             && this.marker != null) {

             this.partial = this.load();

         }

         return !this.partial.isEmpty();

     }

     @Override

     public final String next() {

         if (!this.hasNext()) {

             throw new NoSuchElementException(

                 "There are no more elements in this iterator"

             );

         }

         return this.partial.remove(0);

     }

     @Override

     public final void remove() {

         throw new UnsupportedOperationException("Remove is not supported");

     }

     /**

      * Loads next portion of data from S3.

      * @return A list with next portion of data from S3

      */

     private List<String> load() {

         try {

             final AmazonS3 aws = this.region.aws();

             final long start = System.currentTimeMillis();

             final ObjectListing listing = aws.listObjects(

                 new ListObjectsRequest()

                     .withBucketName(this.bucket)

                     .withPrefix(this.prefix)

                     .withMarker(this.marker)

             );

             this.marker = listing.getNextMarker();

             final List<String> list = new LinkedList<String>();

             for (final S3ObjectSummary sum

                 : listing.getObjectSummaries()) {

                 list.add(sum.getKey());

             }

             Logger.info(

                 this,

                 "listed %d ocket(s) with prefix '%s' in bucket '%s' in %[ms]s",

                 listing.getObjectSummaries().size(), this.prefix,

                 this.bucket, System.currentTimeMillis() - start

             );

             return list;

         } catch (final AmazonServiceException ex) {

             throw new IllegalStateException(

                 String.format(

                     "failed to load a list of objects in '%s', prefix=%s",

                     this.bucket, this.prefix

                 ),

                 ex

             );

         }

     }

 }