    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 * This class is devoted to perform this interpretation. It visits an
    039 * {@link EditScript edit script} (because it implements the
    040 * {@link CommandVisitor CommandVisitor} interface) and calls a user-supplied
    041 * handler implementing the {@link ReplacementsHandler ReplacementsHandler}
    042 * interface to process the sub-sequences.
    043 *
    044 * @see ReplacementsHandler
    045 * @see EditScript
    046 * @see SequencesComparator
    047 *
    048 * @since 4.0
    049 */
    050public class ReplacementsFinder<T> implements CommandVisitor<T> {
    051
    052    private final List<T> pendingInsertions;
    053    private final List<T> pendingDeletions;
    054    private int     skipped;
    055
    056    /** Handler to call when synchronized sequences are found. */
    057    private final ReplacementsHandler<T> handler;
    058
    059    /**
    060     * Simple constructor. Creates a new instance of {@link ReplacementsFinder}.
    061     *
    062     * @param handler  handler to call when synchronized sequences are found
    063     */
    064    public ReplacementsFinder(final ReplacementsHandler<T> handler) {
    065        pendingInsertions = new ArrayList<>();
    066        pendingDeletions  = new ArrayList<>();
    067        skipped           = 0;
    068        this.handler      = handler;
    069    }
    070
    071    /**
    072     * Add an object to the pending insertions set.
    073     *
    074     * @param object  object to insert
    075     */
    076    @Override
    077    public void visitInsertCommand(final T object) {
    078        pendingInsertions.add(object);
    079    }
    080
    081    /**
    082     * Handle a synchronization object.
    083     * <p>
    084     * When a synchronization object is identified, the pending insertions and
    085     * pending deletions sets are provided to the user handler as subsequences.
    086     *
    087     * @param object  synchronization object detected
    088     */
    089    @Override
    090    public void visitKeepCommand(final T object) {
    091        if (pendingDeletions.isEmpty() && pendingInsertions.isEmpty()) {
    092            ++skipped;
    093        } else {
    094            handler.handleReplacement(skipped, pendingDeletions, pendingInsertions);
    095            pendingDeletions.clear();
    096            pendingInsertions.clear();
    097            skipped = 1;
    098        }
    099    }
    100
    101    /**
    102     * Add an object to the pending deletions set.
    103     *
    104     * @param object  object to delete
    105     */
    106    @Override
    107    public void visitDeleteCommand(final T object) {
    108        pendingDeletions.add(object);
    109    }
    110
    111}