1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.text.diff;
18
19 import java.util.ArrayList;
20 import java.util.List;
21
22 /**
23 * This class handles sequences of replacements resulting from a comparison.
24 * <p>
25 * The comparison of two objects sequences leads to the identification of common
26 * parts and parts which only belong to the first or to the second sequence. The
27 * common parts appear in the edit script in the form of <em>keep</em> commands,
28 * they can be considered as synchronization objects between the two sequences.
29 * These synchronization objects split the two sequences in synchronized
30 * sub-sequences. The first sequence can be transformed into the second one by
31 * replacing each synchronized sub-sequence of the first sequence by the
32 * corresponding sub-sequence of the second sequence. This is a synthetic way to
33 * see an {@link EditScript edit script}, replacing individual
34 * {@link DeleteCommand delete}, {@link KeepCommand keep} and
35 * {@link InsertCommand insert} commands by fewer replacements acting on
36 * complete sub-sequences.
37 * </p>
38 * <p>
39 * This class is devoted to perform this interpretation. It visits an
40 * {@link EditScript edit script} (because it implements the
41 * {@link CommandVisitor CommandVisitor} interface) and calls a user-supplied
42 * handler implementing the {@link ReplacementsHandler ReplacementsHandler}
43 * interface to process the sub-sequences.
44 * </p>
45 *
46 * @see ReplacementsHandler
47 * @see EditScript
48 * @see StringsComparator
49 * @param <T> object type
50 * @since 1.0
51 */
52 public class ReplacementsFinder<T> implements CommandVisitor<T> {
53
54 /**
55 * List of pending insertions.
56 */
57 private final List<T> pendingInsertions;
58
59 /**
60 * List of pending deletions.
61 */
62 private final List<T> pendingDeletions;
63
64 /**
65 * Count of elements skipped.
66 */
67 private int skipped;
68
69 /** Handler to call when synchronized sequences are found. */
70 private final ReplacementsHandler<T> handler;
71
72 /**
73 * Constructs a new instance of {@link ReplacementsFinder}.
74 *
75 * @param handler handler to call when synchronized sequences are found
76 */
77 public ReplacementsFinder(final ReplacementsHandler<T> handler) {
78 pendingInsertions = new ArrayList<>();
79 pendingDeletions = new ArrayList<>();
80 skipped = 0;
81 this.handler = handler;
82 }
83
84 /**
85 * Add an object to the pending deletions set.
86 *
87 * @param object object to delete
88 */
89 @Override
90 public void visitDeleteCommand(final T object) {
91 pendingDeletions.add(object);
92 }
93
94 /**
95 * Add an object to the pending insertions set.
96 *
97 * @param object object to insert
98 */
99 @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 }