    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.text.diff;
    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 StringsComparator
    049 * @param <T> object type
    050 * @since 1.0
    051 */
    052public class ReplacementsFinder<T> implements CommandVisitor<T> {
    053
    054    /**
    055     * List of pending insertions.
    056     */
    057    private final List<T> pendingInsertions;
    058
    059    /**
    060     * List of pending deletions.
    061     */
    062    private final List<T> pendingDeletions;
    063
    064    /**
    065     * Count of elements skipped.
    066     */
    067    private int skipped;
    068
    069    /** Handler to call when synchronized sequences are found. */
    070    private final ReplacementsHandler<T> handler;
    071
    072    /**
    073     * Constructs a new instance of {@link ReplacementsFinder}.
    074     *
    075     * @param handler  handler to call when synchronized sequences are found
    076     */
    077    public ReplacementsFinder(final ReplacementsHandler<T> handler) {
    078        pendingInsertions = new ArrayList<>();
    079        pendingDeletions  = new ArrayList<>();
    080        skipped           = 0;
    081        this.handler      = handler;
    082    }
    083
    084    /**
    085     * Add an object to the pending deletions set.
    086     *
    087     * @param object  object to delete
    088     */
    089    @Override
    090    public void visitDeleteCommand(final T object) {
    091        pendingDeletions.add(object);
    092    }
    093
    094    /**
    095     * Add an object to the pending insertions set.
    096     *
    097     * @param object  object to insert
    098     */
    099    @Override
    100    public void visitInsertCommand(final T object) {
    101        pendingInsertions.add(object);
    102    }
    103
    104    /**
    105     * Handle a synchronization object.
    106     * <p>
    107     * When a synchronization object is identified, the pending insertions and
    108     * pending deletions sets are provided to the user handler as subsequences.
    109     * </p>
    110     *
    111     * @param object  synchronization object detected
    112     */
    113    @Override
    114    public void visitKeepCommand(final T object) {
    115        if (pendingDeletions.isEmpty() && pendingInsertions.isEmpty()) {
    116            ++skipped;
    117        } else {
    118            handler.handleReplacement(skipped, pendingDeletions, pendingInsertions);
    119            pendingDeletions.clear();
    120            pendingInsertions.clear();
    121            skipped = 1;
    122        }
    123    }
    124
    125}