    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 *
    050 * @param <T> object type
    051 * @since 1.0
    052 */
    053public class ReplacementsFinder<T> implements CommandVisitor<T> {
    054
    055    /**
    056     * List of pending insertions.
    057     */
    058    private final List<T> pendingInsertions;
    059
    060    /**
    061     * List of pending deletions.
    062     */
    063    private final List<T> pendingDeletions;
    064
    065    /**
    066     * Count of elements skipped.
    067     */
    068    private int skipped;
    069
    070    /** Handler to call when synchronized sequences are found. */
    071    private final ReplacementsHandler<T> handler;
    072
    073    /**
    074     * Simple constructor. Creates a new instance of {@link ReplacementsFinder}.
    075     *
    076     * @param handler  handler to call when synchronized sequences are found
    077     */
    078    public ReplacementsFinder(final ReplacementsHandler<T> handler) {
    079        pendingInsertions = new ArrayList<>();
    080        pendingDeletions  = new ArrayList<>();
    081        skipped           = 0;
    082        this.handler      = handler;
    083    }
    084
    085    /**
    086     * Add an object to the pending insertions set.
    087     *
    088     * @param object  object to insert
    089     */
    090    @Override
    091    public void visitInsertCommand(final T object) {
    092        pendingInsertions.add(object);
    093    }
    094
    095    /**
    096     * Handle a synchronization object.
    097     * <p>
    098     * When a synchronization object is identified, the pending insertions and
    099     * pending deletions sets are provided to the user handler as subsequences.
    100     * </p>
    101     *
    102     * @param object  synchronization object detected
    103     */
    104    @Override
    105    public void visitKeepCommand(final T object) {
    106        if (pendingDeletions.isEmpty() && pendingInsertions.isEmpty()) {
    107            ++skipped;
    108        } else {
    109            handler.handleReplacement(skipped, pendingDeletions, pendingInsertions);
    110            pendingDeletions.clear();
    111            pendingInsertions.clear();
    112            skipped = 1;
    113        }
    114    }
    115
    116    /**
    117     * Add an object to the pending deletions set.
    118     *
    119     * @param object  object to delete
    120     */
    121    @Override
    122    public void visitDeleteCommand(final T object) {
    123        pendingDeletions.add(object);
    124    }
    125
    126}