001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.collections4.sequence;
018
019import java.util.ArrayList;
020import java.util.List;
021
022/**
023 * This class handles sequences of replacements resulting from a comparison.
024 * <p>
025 * The comparison of two objects sequences leads to the identification of common
026 * parts and parts which only belong to the first or to the second sequence. The
027 * common parts appear in the edit script in the form of <em>keep</em> commands,
028 * they can be considered as synchronization objects between the two sequences.
029 * These synchronization objects split the two sequences in synchronized
030 * sub-sequences. The first sequence can be transformed into the second one by
031 * replacing each synchronized sub-sequence of the first sequence by the
032 * corresponding sub-sequence of the second sequence. This is a synthetic way to
033 * see an {@link EditScript edit script}, replacing individual
034 * {@link DeleteCommand delete}, {@link KeepCommand keep} and
035 * {@link InsertCommand insert} commands by fewer replacements acting on
036 * complete sub-sequences.
037 * </p>
038 * <p>
039 * This class is devoted to perform this interpretation. It visits an
040 * {@link EditScript edit script} (because it implements the
041 * {@link CommandVisitor CommandVisitor} interface) and calls a user-supplied
042 * handler implementing the {@link ReplacementsHandler ReplacementsHandler}
043 * interface to process the sub-sequences.
044 * </p>
045 *
046 * @see ReplacementsHandler
047 * @see EditScript
048 * @see SequencesComparator
049 *
050 * @since 4.0
051 */
052public class ReplacementsFinder<T> implements CommandVisitor<T> {
053
054    private final List<T> pendingInsertions;
055    private final List<T> pendingDeletions;
056    private int     skipped;
057
058    /** Handler to call when synchronized sequences are found. */
059    private final ReplacementsHandler<T> handler;
060
061    /**
062     * Simple constructor. Creates a new instance of {@link ReplacementsFinder}.
063     *
064     * @param handler  handler to call when synchronized sequences are found
065     */
066    public ReplacementsFinder(final ReplacementsHandler<T> handler) {
067        pendingInsertions = new ArrayList<>();
068        pendingDeletions  = new ArrayList<>();
069        skipped           = 0;
070        this.handler      = handler;
071    }
072
073    /**
074     * Add an object to the pending insertions set.
075     *
076     * @param object  object to insert
077     */
078    @Override
079    public void visitInsertCommand(final T object) {
080        pendingInsertions.add(object);
081    }
082
083    /**
084     * Handle a synchronization object.
085     * <p>
086     * When a synchronization object is identified, the pending insertions and
087     * pending deletions sets are provided to the user handler as subsequences.
088     *
089     * @param object  synchronization object detected
090     */
091    @Override
092    public void visitKeepCommand(final T object) {
093        if (pendingDeletions.isEmpty() && pendingInsertions.isEmpty()) {
094            ++skipped;
095        } else {
096            handler.handleReplacement(skipped, pendingDeletions, pendingInsertions);
097            pendingDeletions.clear();
098            pendingInsertions.clear();
099            skipped = 1;
100        }
101    }
102
103    /**
104     * Add an object to the pending deletions set.
105     *
106     * @param object  object to delete
107     */
108    @Override
109    public void visitDeleteCommand(final T object) {
110        pendingDeletions.add(object);
111    }
112
113}