001/**
002 * Copyright (c) 2011, The University of Southampton and the individual contributors.
003 * All rights reserved.
004 *
005 * Redistribution and use in source and binary forms, with or without modification,
006 * are permitted provided that the following conditions are met:
007 *
008 *   *  Redistributions of source code must retain the above copyright notice,
009 *      this list of conditions and the following disclaimer.
010 *
011 *   *  Redistributions in binary form must reproduce the above copyright notice,
012 *      this list of conditions and the following disclaimer in the documentation
013 *      and/or other materials provided with the distribution.
014 *
015 *   *  Neither the name of the University of Southampton nor the names of its
016 *      contributors may be used to endorse or promote products derived from this
017 *      software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
020 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
021 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
022 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
023 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
026 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
028 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package org.openimaj.util.stream.window;
031
032import java.util.ArrayList;
033import java.util.Comparator;
034import java.util.List;
035
036import org.openimaj.util.function.Function;
037import org.openimaj.util.stream.AbstractStream;
038import org.openimaj.util.stream.Stream;
039
040/**
041 * @author Sina Samangooei (ss@ecs.soton.ac.uk)
042 * @param <T>
043 *
044 */
045public abstract class SequentialStreamAggregator<T>
046                implements
047                        Function<Stream<T>, Stream<T>>
048{
049
050        private Comparator<T> comp;
051
052        /**
053         * @param comp the comparator for decided whether sequential items are the same
054         */
055        public SequentialStreamAggregator(Comparator<T> comp) {
056                this.comp = comp;
057        }
058
059        @Override
060        public Stream<T> apply(final Stream<T> inner) {
061                return new AbstractStream<T>() {
062
063                        List<T> currentList = new ArrayList<T>();
064                        @Override
065                        public boolean hasNext() {
066                                return inner.hasNext() || currentList.size() != 0;
067                        }
068                        @Override
069                        public T next() {
070                                while(inner.hasNext()){
071                                        T next = inner.next();
072                                        if(currentList.size() == 0 || comp.compare(currentList.get(0), next) == 0){
073                                                currentList.add(next);
074                                        }
075                                        else{
076                                                T toRet = combine(currentList);
077                                                currentList.clear();
078                                                currentList.add(next);
079                                                return toRet;
080                                        }
081                                }
082                                // The end of the stream is reached
083                                if(currentList.size()!=0){
084                                        T toRet = combine(currentList);
085                                        currentList.clear();
086                                        return toRet;
087                                }
088                                else{
089                                        throw new UnsupportedOperationException("The sequential combiner failed");
090                                }
091                        }
092                };
093        }
094
095        /**
096         * Called when a window of identical items needs to be combined
097         * @param window
098         *
099         * @return the combination of the current and next values
100         */
101        public abstract T combine(List<T> window) ;
102
103
104}