    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 *      https://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 * @param <T> The type of the input to the visit operations.
    047 * @see ReplacementsHandler
    048 * @see EditScript
    049 * @see SequencesComparator
    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 deletions set.
    075     *
    076     * @param object  object to delete
    077     */
    078    @Override
    079    public void visitDeleteCommand(final T object) {
    080        pendingDeletions.add(object);
    081    }
    082
    083    /**
    084     * Add an object to the pending insertions set.
    085     *
    086     * @param object  object to insert
    087     */
    088    @Override
    089    public void visitInsertCommand(final T object) {
    090        pendingInsertions.add(object);
    091    }
    092
    093    /**
    094     * Handle a synchronization object.
    095     * <p>
    096     * When a synchronization object is identified, the pending insertions and
    097     * pending deletions sets are provided to the user handler as subsequences.
    098     *
    099     * @param object  synchronization object detected
    100     */
    101    @Override
    102    public void visitKeepCommand(final T object) {
    103        if (pendingDeletions.isEmpty() && pendingInsertions.isEmpty()) {
    104            ++skipped;
    105        } else {
    106            handler.handleReplacement(skipped, pendingDeletions, pendingInsertions);
    107            pendingDeletions.clear();
    108            pendingInsertions.clear();
    109            skipped = 1;
    110        }
    111    }
    112
    113}