1478 lines
56 KiB
Dart
1478 lines
56 KiB
Dart
/*
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* Diff Match and Patch
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* Copyright 2018 The diff-match-patch Authors.
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* https://github.com/google/diff-match-patch
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/*
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* Functions for diff, match and patch.
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* Computes the difference between two texts to create a patch.
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* Applies the patch onto another text, allowing for errors.
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*
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* @author fraser@google.com (Neil Fraser)
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*/
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// ignore_for_file: no_leading_underscores_for_local_identifiers
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// ignore_for_file: non_constant_identifier_names
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// ignore_for_file: unnecessary_this
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import 'dart:collection';
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import 'dart:math';
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// adapted from Google's `Diff Match and Patch` Dart implementation
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// cf https://github.com/google/diff-match-patch/tree/master/dart
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/// Class representing one diff operation.
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class Diff {
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/// One of: Operation.insert, Operation.delete or Operation.equal.
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Operation operation;
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/// The text associated with this diff operation.
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String text;
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/// Constructor. Initializes the diff with the provided values.
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/// [operation] is one of Operation.insert, Operation.delete or Operation.equal.
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/// [text] is the text being applied.
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Diff(this.operation, this.text);
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/// Display a human-readable version of this Diff.
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/// Returns a text version.
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@override
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String toString() {
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String prettyText = this.text.replaceAll('\n', '\u00b6');
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return 'Diff(${this.operation},"$prettyText")';
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}
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/// Is this Diff equivalent to another Diff?
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/// [other] is another Diff to compare against.
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/// Returns true or false.
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@override
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bool operator ==(Object other) => identical(this, other) || other is Diff && runtimeType == other.runtimeType && operation == other.operation && text == other.text;
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/// Generate a uniquely identifiable hashcode for this Diff.
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/// Returns numeric hashcode.
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@override
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int get hashCode => operation.hashCode ^ text.hashCode;
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}
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/// The data structure representing a diff is a List of Diff objects:
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/// {Diff(Operation.delete, 'Hello'), Diff(Operation.insert, 'Goodbye'),
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/// Diff(Operation.equal, ' world.')}
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/// which means: delete 'Hello', add 'Goodbye' and keep ' world.'
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enum Operation { delete, insert, equal }
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/// Class containing the diff, match and patch methods.
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/// Also contains the behaviour settings.
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class DiffMatchPatch {
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// Defaults.
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// Set these on your diff_match_patch instance to override the defaults.
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/// Number of seconds to map a diff before giving up (0 for infinity).
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double Diff_Timeout = 1.0;
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/// Cost of an empty edit operation in terms of edit characters.
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int Diff_EditCost = 4;
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/// At what point is no match declared (0.0 = perfection, 1.0 = very loose).
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double Match_Threshold = 0.5;
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/// How far to search for a match (0 = exact location, 1000+ = broad match).
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/// A match this many characters away from the expected location will add
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/// 1.0 to the score (0.0 is a perfect match).
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int Match_Distance = 1000;
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/// When deleting a large block of text (over ~64 characters), how close do
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/// the contents have to be to match the expected contents. (0.0 = perfection,
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/// 1.0 = very loose). Note that Match_Threshold controls how closely the
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/// end points of a delete need to match.
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double Patch_DeleteThreshold = 0.5;
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/// Chunk size for context length.
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int Patch_Margin = 4;
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/// The number of bits in an int.
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int Match_MaxBits = 32;
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// DIFF FUNCTIONS
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/// Find the differences between two texts. Simplifies the problem by
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/// stripping any common prefix or suffix off the texts before diffing.
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/// [text1] is the old string to be diffed.
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/// [text2] is the new string to be diffed.
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/// [checklines] is an optional speedup flag. If present and false, then don't
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/// run a line-level diff first to identify the changed areas.
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/// Defaults to true, which does a faster, slightly less optimal diff.
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/// [deadline] is an optional time when the diff should be complete by. Used
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/// internally for recursive calls. Users should set DiffTimeout instead.
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/// Returns a List of Diff objects.
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List<Diff> diff_main(String? text1, String? text2, [bool checklines = true, DateTime? deadline]) {
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// Set a deadline by which time the diff must be complete.
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if (deadline == null) {
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deadline = DateTime.now();
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if (Diff_Timeout <= 0) {
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// One year should be sufficient for 'infinity'.
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deadline = deadline.add(const Duration(days: 365));
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} else {
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deadline = deadline.add(Duration(milliseconds: (Diff_Timeout * 1000).toInt()));
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}
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}
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// Check for null inputs.
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if (text1 == null || text2 == null) {
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throw ArgumentError('Null inputs. (diff_main)');
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}
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// Check for equality (speedup).
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List<Diff> diffs;
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if (text1 == text2) {
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diffs = [];
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if (text1.isNotEmpty) {
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diffs.add(Diff(Operation.equal, text1));
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}
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return diffs;
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}
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// Trim off common prefix (speedup).
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int commonlength = diff_commonPrefix(text1, text2);
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String commonprefix = text1.substring(0, commonlength);
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text1 = text1.substring(commonlength);
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text2 = text2.substring(commonlength);
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// Trim off common suffix (speedup).
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commonlength = diff_commonSuffix(text1, text2);
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String commonsuffix = text1.substring(text1.length - commonlength);
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text1 = text1.substring(0, text1.length - commonlength);
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text2 = text2.substring(0, text2.length - commonlength);
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// Compute the diff on the middle block.
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diffs = _diff_compute(text1, text2, checklines, deadline);
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// Restore the prefix and suffix.
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if (commonprefix.isNotEmpty) {
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diffs.insert(0, Diff(Operation.equal, commonprefix));
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}
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if (commonsuffix.isNotEmpty) {
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diffs.add(Diff(Operation.equal, commonsuffix));
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}
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diff_cleanupMerge(diffs);
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return diffs;
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}
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/// Find the differences between two texts. Assumes that the texts do not
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/// have any common prefix or suffix.
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/// [text1] is the old string to be diffed.
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/// [text2] is the new string to be diffed.
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/// [checklines] is a speedup flag. If false, then don't run a
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/// line-level diff first to identify the changed areas.
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/// If true, then run a faster slightly less optimal diff.
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/// [deadline] is the time when the diff should be complete by.
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/// Returns a List of Diff objects.
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List<Diff> _diff_compute(String text1, String text2, bool checklines, DateTime deadline) {
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List<Diff> diffs = <Diff>[];
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if (text1.isEmpty) {
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// Just add some text (speedup).
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diffs.add(Diff(Operation.insert, text2));
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return diffs;
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}
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if (text2.isEmpty) {
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// Just delete some text (speedup).
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diffs.add(Diff(Operation.delete, text1));
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return diffs;
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}
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String longtext = text1.length > text2.length ? text1 : text2;
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String shorttext = text1.length > text2.length ? text2 : text1;
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int i = longtext.indexOf(shorttext);
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if (i != -1) {
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// Shorter text is inside the longer text (speedup).
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Operation op = (text1.length > text2.length) ? Operation.delete : Operation.insert;
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diffs.add(Diff(op, longtext.substring(0, i)));
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diffs.add(Diff(Operation.equal, shorttext));
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diffs.add(Diff(op, longtext.substring(i + shorttext.length)));
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return diffs;
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}
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if (shorttext.length == 1) {
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// Single character string.
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// After the previous speedup, the character can't be an equality.
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diffs.add(Diff(Operation.delete, text1));
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diffs.add(Diff(Operation.insert, text2));
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return diffs;
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}
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// Check to see if the problem can be split in two.
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final hm = _diff_halfMatch(text1, text2);
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if (hm != null) {
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// A half-match was found, sort out the return data.
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final text1_a = hm[0];
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final text1_b = hm[1];
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final text2_a = hm[2];
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final text2_b = hm[3];
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final mid_common = hm[4];
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// Send both pairs off for separate processing.
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final diffs_a = diff_main(text1_a, text2_a, checklines, deadline);
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final diffs_b = diff_main(text1_b, text2_b, checklines, deadline);
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// Merge the results.
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diffs = diffs_a;
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diffs.add(Diff(Operation.equal, mid_common));
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diffs.addAll(diffs_b);
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return diffs;
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}
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if (checklines && text1.length > 100 && text2.length > 100) {
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return _diff_lineMode(text1, text2, deadline);
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}
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return _diff_bisect(text1, text2, deadline);
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}
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/// Do a quick line-level diff on both strings, then rediff the parts for
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/// greater accuracy.
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/// This speedup can produce non-minimal diffs.
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/// [text1] is the old string to be diffed.
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/// [text2] is the new string to be diffed.
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/// [deadline] is the time when the diff should be complete by.
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/// Returns a List of Diff objects.
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List<Diff> _diff_lineMode(String text1, String text2, DateTime deadline) {
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// Scan the text on a line-by-line basis first.
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final a = _diff_linesToChars(text1, text2);
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text1 = a['chars1'];
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text2 = a['chars2'];
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final linearray = a['lineArray'];
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final diffs = diff_main(text1, text2, false, deadline);
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// Convert the diff back to original text.
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_diff_charsToLines(diffs, linearray);
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// Eliminate freak matches (e.g. blank lines)
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diff_cleanupSemantic(diffs);
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// Rediff any replacement blocks, this time character-by-character.
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// Add a dummy entry at the end.
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diffs.add(Diff(Operation.equal, ''));
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int pointer = 0;
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int count_delete = 0;
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int count_insert = 0;
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final text_delete = StringBuffer();
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final text_insert = StringBuffer();
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while (pointer < diffs.length) {
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switch (diffs[pointer].operation) {
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case Operation.insert:
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count_insert++;
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text_insert.write(diffs[pointer].text);
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case Operation.delete:
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count_delete++;
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text_delete.write(diffs[pointer].text);
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case Operation.equal:
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// Upon reaching an equality, check for prior redundancies.
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if (count_delete >= 1 && count_insert >= 1) {
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// Delete the offending records and add the merged ones.
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diffs.removeRange(pointer - count_delete - count_insert, pointer);
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pointer = pointer - count_delete - count_insert;
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final subDiff = diff_main(text_delete.toString(), text_insert.toString(), false, deadline);
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for (int j = subDiff.length - 1; j >= 0; j--) {
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diffs.insert(pointer, subDiff[j]);
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}
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pointer = pointer + subDiff.length;
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}
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count_insert = 0;
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count_delete = 0;
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text_delete.clear();
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text_insert.clear();
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}
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pointer++;
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}
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diffs.removeLast(); // Remove the dummy entry at the end.
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return diffs;
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}
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/// Find the 'middle snake' of a diff, split the problem in two
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/// and return the recursively constructed diff.
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/// See Myers 1986 paper: An O(ND) Difference Algorithm and Its Variations.
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/// [text1] is the old string to be diffed.
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/// [text2] is the new string to be diffed.
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/// [deadline] is the time at which to bail if not yet complete.
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/// Returns a List of Diff objects.
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List<Diff> _diff_bisect(String text1, String text2, DateTime deadline) {
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// Cache the text lengths to prevent multiple calls.
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final text1_length = text1.length;
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final text2_length = text2.length;
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final max_d = (text1_length + text2_length + 1) ~/ 2;
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final v_offset = max_d;
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final v_length = 2 * max_d;
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final v1 = List<int>.filled(v_length, -1);
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final v2 = List<int>.filled(v_length, -1);
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v1[v_offset + 1] = 0;
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v2[v_offset + 1] = 0;
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final delta = text1_length - text2_length;
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// If the total number of characters is odd, then the front path will
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// collide with the reverse path.
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final front = (delta % 2 != 0);
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// Offsets for start and end of k loop.
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// Prevents mapping of space beyond the grid.
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int k1start = 0;
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int k1end = 0;
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int k2start = 0;
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int k2end = 0;
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for (int d = 0; d < max_d; d++) {
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// Bail out if deadline is reached.
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if ((DateTime.now()).compareTo(deadline) == 1) {
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break;
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}
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// Walk the front path one step.
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for (int k1 = -d + k1start; k1 <= d - k1end; k1 += 2) {
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int k1_offset = v_offset + k1;
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int x1;
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if (k1 == -d || k1 != d && v1[k1_offset - 1] < v1[k1_offset + 1]) {
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x1 = v1[k1_offset + 1];
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} else {
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x1 = v1[k1_offset - 1] + 1;
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}
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int y1 = x1 - k1;
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while (x1 < text1_length && y1 < text2_length && text1[x1] == text2[y1]) {
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x1++;
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y1++;
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}
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v1[k1_offset] = x1;
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if (x1 > text1_length) {
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// Ran off the right of the graph.
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k1end += 2;
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} else if (y1 > text2_length) {
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// Ran off the bottom of the graph.
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k1start += 2;
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} else if (front) {
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int k2_offset = v_offset + delta - k1;
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if (k2_offset >= 0 && k2_offset < v_length && v2[k2_offset] != -1) {
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// Mirror x2 onto top-left coordinate system.
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int x2 = text1_length - v2[k2_offset];
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if (x1 >= x2) {
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// Overlap detected.
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return _diff_bisectSplit(text1, text2, x1, y1, deadline);
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}
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}
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}
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}
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// Walk the reverse path one step.
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for (int k2 = -d + k2start; k2 <= d - k2end; k2 += 2) {
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int k2_offset = v_offset + k2;
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int x2;
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if (k2 == -d || k2 != d && v2[k2_offset - 1] < v2[k2_offset + 1]) {
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x2 = v2[k2_offset + 1];
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} else {
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x2 = v2[k2_offset - 1] + 1;
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}
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int y2 = x2 - k2;
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while (x2 < text1_length && y2 < text2_length && text1[text1_length - x2 - 1] == text2[text2_length - y2 - 1]) {
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x2++;
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y2++;
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}
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v2[k2_offset] = x2;
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if (x2 > text1_length) {
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// Ran off the left of the graph.
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k2end += 2;
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} else if (y2 > text2_length) {
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// Ran off the top of the graph.
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k2start += 2;
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} else if (!front) {
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int k1_offset = v_offset + delta - k2;
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if (k1_offset >= 0 && k1_offset < v_length && v1[k1_offset] != -1) {
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int x1 = v1[k1_offset];
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int y1 = v_offset + x1 - k1_offset;
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// Mirror x2 onto top-left coordinate system.
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x2 = text1_length - x2;
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if (x1 >= x2) {
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// Overlap detected.
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return _diff_bisectSplit(text1, text2, x1, y1, deadline);
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}
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}
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}
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}
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}
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// Diff took too long and hit the deadline or
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// number of diffs equals number of characters, no commonality at all.
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return [Diff(Operation.delete, text1), Diff(Operation.insert, text2)];
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}
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/// Hack to allow unit tests to call private method. Do not use.
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List<Diff> test_diff_bisect(String text1, String text2, DateTime deadline) {
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return _diff_bisect(text1, text2, deadline);
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}
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/// Given the location of the 'middle snake', split the diff in two parts
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/// and recurse.
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/// [text1] is the old string to be diffed.
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/// [text2] is the new string to be diffed.
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/// [x] is the index of split point in text1.
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/// [y] is the index of split point in text2.
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/// [deadline] is the time at which to bail if not yet complete.
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/// Returns a List of Diff objects.
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List<Diff> _diff_bisectSplit(String text1, String text2, int x, int y, DateTime deadline) {
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final text1a = text1.substring(0, x);
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final text2a = text2.substring(0, y);
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final text1b = text1.substring(x);
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final text2b = text2.substring(y);
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// Compute both diffs serially.
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final diffs = diff_main(text1a, text2a, false, deadline);
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final diffsb = diff_main(text1b, text2b, false, deadline);
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diffs.addAll(diffsb);
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return diffs;
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}
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/// Split two texts into a list of strings. Reduce the texts to a string of
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/// hashes where each Unicode character represents one line.
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/// [text1] is the first string.
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/// [text2] is the second string.
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/// Returns a Map containing the encoded text1, the encoded text2 and
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/// the List of unique strings. The zeroth element of the List of
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/// unique strings is intentionally blank.
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Map<String, dynamic> _diff_linesToChars(String text1, String text2) {
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final lineArray = <String>[];
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final lineHash = HashMap<String, int>();
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// e.g. linearray[4] == 'Hello\n'
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// e.g. linehash['Hello\n'] == 4
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// '\x00' is a valid character, but various debuggers don't like it.
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// So we'll insert a junk entry to avoid generating a null character.
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lineArray.add('');
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// Allocate 2/3rds of the space for text1, the rest for text2.
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String chars1 = _diff_linesToCharsMunge(text1, lineArray, lineHash, 40000);
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String chars2 = _diff_linesToCharsMunge(text2, lineArray, lineHash, 65535);
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return {'chars1': chars1, 'chars2': chars2, 'lineArray': lineArray};
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}
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/// Hack to allow unit tests to call private method. Do not use.
|
|
Map<String, dynamic> test_diff_linesToChars(String text1, String text2) {
|
|
return _diff_linesToChars(text1, text2);
|
|
}
|
|
|
|
/// Split a text into a list of strings. Reduce the texts to a string of
|
|
/// hashes where each Unicode character represents one line.
|
|
/// [text] is the string to encode.
|
|
/// [lineArray] is a List of unique strings.
|
|
/// [lineHash] is a Map of strings to indices.
|
|
/// [maxLines] is the maximum length for lineArray.
|
|
/// Returns an encoded string.
|
|
String _diff_linesToCharsMunge(String text, List<String> lineArray, Map<String, int> lineHash, int maxLines) {
|
|
int lineStart = 0;
|
|
int lineEnd = -1;
|
|
String line;
|
|
final chars = StringBuffer();
|
|
// Walk the text, pulling out a substring for each line.
|
|
// text.split('\n') would would temporarily double our memory footprint.
|
|
// Modifying text would create many large strings to garbage collect.
|
|
while (lineEnd < text.length - 1) {
|
|
lineEnd = text.indexOf('\n', lineStart);
|
|
if (lineEnd == -1) {
|
|
lineEnd = text.length - 1;
|
|
}
|
|
line = text.substring(lineStart, lineEnd + 1);
|
|
|
|
if (lineHash.containsKey(line)) {
|
|
chars.writeCharCode(lineHash[line]!);
|
|
} else {
|
|
if (lineArray.length == maxLines) {
|
|
// Bail out at 65535 because
|
|
// final chars1 = StringBuffer();
|
|
// chars1.writeCharCode(65536);
|
|
// chars1.toString().codeUnitAt(0) == 55296;
|
|
line = text.substring(lineStart);
|
|
lineEnd = text.length;
|
|
}
|
|
lineArray.add(line);
|
|
lineHash[line] = lineArray.length - 1;
|
|
chars.writeCharCode(lineArray.length - 1);
|
|
}
|
|
lineStart = lineEnd + 1;
|
|
}
|
|
return chars.toString();
|
|
}
|
|
|
|
/// Rehydrate the text in a diff from a string of line hashes to real lines of
|
|
/// text.
|
|
/// [diffs] is a List of Diff objects.
|
|
/// [lineArray] is a List of unique strings.
|
|
void _diff_charsToLines(List<Diff> diffs, List<String> lineArray) {
|
|
final text = StringBuffer();
|
|
for (Diff diff in diffs) {
|
|
for (int j = 0; j < diff.text.length; j++) {
|
|
text.write(lineArray[diff.text.codeUnitAt(j)]);
|
|
}
|
|
diff.text = text.toString();
|
|
text.clear();
|
|
}
|
|
}
|
|
|
|
/// Hack to allow unit tests to call private method. Do not use.
|
|
void test_diff_charsToLines(List<Diff> diffs, List<String> lineArray) {
|
|
_diff_charsToLines(diffs, lineArray);
|
|
}
|
|
|
|
/// Determine the common prefix of two strings
|
|
/// [text1] is the first string.
|
|
/// [text2] is the second string.
|
|
/// Returns the number of characters common to the start of each string.
|
|
int diff_commonPrefix(String text1, String text2) {
|
|
// TODO: Once Dart's performance stabilizes, determine if linear or binary
|
|
// search is better.
|
|
// Performance analysis: https://neil.fraser.name/news/2007/10/09/
|
|
final n = min(text1.length, text2.length);
|
|
for (int i = 0; i < n; i++) {
|
|
if (text1[i] != text2[i]) {
|
|
return i;
|
|
}
|
|
}
|
|
return n;
|
|
}
|
|
|
|
/// Determine the common suffix of two strings
|
|
/// [text1] is the first string.
|
|
/// [text2] is the second string.
|
|
/// Returns the number of characters common to the end of each string.
|
|
int diff_commonSuffix(String text1, String text2) {
|
|
// TODO: Once Dart's performance stabilizes, determine if linear or binary
|
|
// search is better.
|
|
// Performance analysis: https://neil.fraser.name/news/2007/10/09/
|
|
final text1_length = text1.length;
|
|
final text2_length = text2.length;
|
|
final n = min(text1_length, text2_length);
|
|
for (int i = 1; i <= n; i++) {
|
|
if (text1[text1_length - i] != text2[text2_length - i]) {
|
|
return i - 1;
|
|
}
|
|
}
|
|
return n;
|
|
}
|
|
|
|
/// Determine if the suffix of one string is the prefix of another.
|
|
/// [text1] is the first string.
|
|
/// [text2] is the second string.
|
|
/// Returns the number of characters common to the end of the first
|
|
/// string and the start of the second string.
|
|
int _diff_commonOverlap(String text1, String text2) {
|
|
// Eliminate the null case.
|
|
if (text1.isEmpty || text2.isEmpty) {
|
|
return 0;
|
|
}
|
|
// Cache the text lengths to prevent multiple calls.
|
|
final text1_length = text1.length;
|
|
final text2_length = text2.length;
|
|
// Truncate the longer string.
|
|
if (text1_length > text2_length) {
|
|
text1 = text1.substring(text1_length - text2_length);
|
|
} else if (text1_length < text2_length) {
|
|
text2 = text2.substring(0, text1_length);
|
|
}
|
|
final text_length = min(text1_length, text2_length);
|
|
// Quick check for the worst case.
|
|
if (text1 == text2) {
|
|
return text_length;
|
|
}
|
|
|
|
// Start by looking for a single character match
|
|
// and increase length until no match is found.
|
|
// Performance analysis: https://neil.fraser.name/news/2010/11/04/
|
|
int best = 0;
|
|
int length = 1;
|
|
while (true) {
|
|
String pattern = text1.substring(text_length - length);
|
|
int found = text2.indexOf(pattern);
|
|
if (found == -1) {
|
|
return best;
|
|
}
|
|
length += found;
|
|
if (found == 0 || text1.substring(text_length - length) == text2.substring(0, length)) {
|
|
best = length;
|
|
length++;
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Hack to allow unit tests to call private method. Do not use.
|
|
int test_diff_commonOverlap(String text1, String text2) {
|
|
return _diff_commonOverlap(text1, text2);
|
|
}
|
|
|
|
/// Do the two texts share a substring which is at least half the length of
|
|
/// the longer text?
|
|
/// This speedup can produce non-minimal diffs.
|
|
/// [text1] is the first string.
|
|
/// [text2] is the second string.
|
|
/// Returns a five element List of Strings, containing the prefix of text1,
|
|
/// the suffix of text1, the prefix of text2, the suffix of text2 and the
|
|
/// common middle. Or null if there was no match.
|
|
List<String>? _diff_halfMatch(String text1, String text2) {
|
|
if (Diff_Timeout <= 0) {
|
|
// Don't risk returning a non-optimal diff if we have unlimited time.
|
|
return null;
|
|
}
|
|
final longtext = text1.length > text2.length ? text1 : text2;
|
|
final shorttext = text1.length > text2.length ? text2 : text1;
|
|
if (longtext.length < 4 || shorttext.length * 2 < longtext.length) {
|
|
return null; // Pointless.
|
|
}
|
|
|
|
// First check if the second quarter is the seed for a half-match.
|
|
final hm1 = _diff_halfMatchI(longtext, shorttext, ((longtext.length + 3) / 4).ceil().toInt());
|
|
// Check again based on the third quarter.
|
|
final hm2 = _diff_halfMatchI(longtext, shorttext, ((longtext.length + 1) / 2).ceil().toInt());
|
|
List<String> hm;
|
|
if (hm1 == null && hm2 == null) {
|
|
return null;
|
|
} else if (hm2 == null) {
|
|
hm = hm1!;
|
|
} else if (hm1 == null) {
|
|
hm = hm2;
|
|
} else {
|
|
// Both matched. Select the longest.
|
|
hm = hm1[4].length > hm2[4].length ? hm1 : hm2;
|
|
}
|
|
|
|
// A half-match was found, sort out the return data.
|
|
if (text1.length > text2.length) {
|
|
return hm;
|
|
//return [hm[0], hm[1], hm[2], hm[3], hm[4]];
|
|
} else {
|
|
return [hm[2], hm[3], hm[0], hm[1], hm[4]];
|
|
}
|
|
}
|
|
|
|
/// Hack to allow unit tests to call private method. Do not use.
|
|
List<String>? test_diff_halfMatch(String text1, String text2) {
|
|
return _diff_halfMatch(text1, text2);
|
|
}
|
|
|
|
/// Does a substring of shorttext exist within longtext such that the
|
|
/// substring is at least half the length of longtext?
|
|
/// [longtext] is the longer string.
|
|
/// [shorttext is the shorter string.
|
|
/// [i] Start index of quarter length substring within longtext.
|
|
/// Returns a five element String array, containing the prefix of longtext,
|
|
/// the suffix of longtext, the prefix of shorttext, the suffix of
|
|
/// shorttext and the common middle. Or null if there was no match.
|
|
List<String>? _diff_halfMatchI(String longtext, String shorttext, int i) {
|
|
// Start with a 1/4 length substring at position i as a seed.
|
|
final seed = longtext.substring(i, i + (longtext.length / 4).floor().toInt());
|
|
int j = -1;
|
|
String best_common = '';
|
|
String best_longtext_a = '', best_longtext_b = '';
|
|
String best_shorttext_a = '', best_shorttext_b = '';
|
|
while ((j = shorttext.indexOf(seed, j + 1)) != -1) {
|
|
int prefixLength = diff_commonPrefix(longtext.substring(i), shorttext.substring(j));
|
|
int suffixLength = diff_commonSuffix(longtext.substring(0, i), shorttext.substring(0, j));
|
|
if (best_common.length < suffixLength + prefixLength) {
|
|
best_common = shorttext.substring(j - suffixLength, j) + shorttext.substring(j, j + prefixLength);
|
|
best_longtext_a = longtext.substring(0, i - suffixLength);
|
|
best_longtext_b = longtext.substring(i + prefixLength);
|
|
best_shorttext_a = shorttext.substring(0, j - suffixLength);
|
|
best_shorttext_b = shorttext.substring(j + prefixLength);
|
|
}
|
|
}
|
|
if (best_common.length * 2 >= longtext.length) {
|
|
return [best_longtext_a, best_longtext_b, best_shorttext_a, best_shorttext_b, best_common];
|
|
} else {
|
|
return null;
|
|
}
|
|
}
|
|
|
|
/// Reduce the number of edits by eliminating semantically trivial equalities.
|
|
/// [diffs] is a List of Diff objects.
|
|
void diff_cleanupSemantic(List<Diff> diffs) {
|
|
bool changes = false;
|
|
// Stack of indices where equalities are found.
|
|
final equalities = <int>[];
|
|
// Always equal to diffs[equalities.last()].text
|
|
String? lastEquality;
|
|
int pointer = 0; // Index of current position.
|
|
// Number of characters that changed prior to the equality.
|
|
int length_insertions1 = 0;
|
|
int length_deletions1 = 0;
|
|
// Number of characters that changed after the equality.
|
|
int length_insertions2 = 0;
|
|
int length_deletions2 = 0;
|
|
while (pointer < diffs.length) {
|
|
if (diffs[pointer].operation == Operation.equal) {
|
|
// Equality found.
|
|
equalities.add(pointer);
|
|
length_insertions1 = length_insertions2;
|
|
length_deletions1 = length_deletions2;
|
|
length_insertions2 = 0;
|
|
length_deletions2 = 0;
|
|
lastEquality = diffs[pointer].text;
|
|
} else {
|
|
// An insertion or deletion.
|
|
if (diffs[pointer].operation == Operation.insert) {
|
|
length_insertions2 += diffs[pointer].text.length;
|
|
} else {
|
|
length_deletions2 += diffs[pointer].text.length;
|
|
}
|
|
// Eliminate an equality that is smaller or equal to the edits on both
|
|
// sides of it.
|
|
if (lastEquality != null && (lastEquality.length <= max(length_insertions1, length_deletions1)) && (lastEquality.length <= max(length_insertions2, length_deletions2))) {
|
|
// Duplicate record.
|
|
diffs.insert(equalities.last, Diff(Operation.delete, lastEquality));
|
|
// Change second copy to insert.
|
|
diffs[equalities.last + 1].operation = Operation.insert;
|
|
// Throw away the equality we just deleted.
|
|
equalities.removeLast();
|
|
// Throw away the previous equality (it needs to be reevaluated).
|
|
if (equalities.isNotEmpty) {
|
|
equalities.removeLast();
|
|
}
|
|
pointer = equalities.isEmpty ? -1 : equalities.last;
|
|
length_insertions1 = 0; // Reset the counters.
|
|
length_deletions1 = 0;
|
|
length_insertions2 = 0;
|
|
length_deletions2 = 0;
|
|
lastEquality = null;
|
|
changes = true;
|
|
}
|
|
}
|
|
pointer++;
|
|
}
|
|
|
|
// Normalize the diff.
|
|
if (changes) {
|
|
diff_cleanupMerge(diffs);
|
|
}
|
|
_diff_cleanupSemanticLossless(diffs);
|
|
|
|
// Find any overlaps between deletions and insertions.
|
|
// e.g: <del>abcxxx</del><ins>xxxdef</ins>
|
|
// -> <del>abc</del>xxx<ins>def</ins>
|
|
// e.g: <del>xxxabc</del><ins>defxxx</ins>
|
|
// -> <ins>def</ins>xxx<del>abc</del>
|
|
// Only extract an overlap if it is as big as the edit ahead or behind it.
|
|
pointer = 1;
|
|
while (pointer < diffs.length) {
|
|
if (diffs[pointer - 1].operation == Operation.delete && diffs[pointer].operation == Operation.insert) {
|
|
String deletion = diffs[pointer - 1].text;
|
|
String insertion = diffs[pointer].text;
|
|
int overlap_length1 = _diff_commonOverlap(deletion, insertion);
|
|
int overlap_length2 = _diff_commonOverlap(insertion, deletion);
|
|
if (overlap_length1 >= overlap_length2) {
|
|
if (overlap_length1 >= deletion.length / 2 || overlap_length1 >= insertion.length / 2) {
|
|
// Overlap found.
|
|
// Insert an equality and trim the surrounding edits.
|
|
diffs.insert(pointer, Diff(Operation.equal, insertion.substring(0, overlap_length1)));
|
|
diffs[pointer - 1].text = deletion.substring(0, deletion.length - overlap_length1);
|
|
diffs[pointer + 1].text = insertion.substring(overlap_length1);
|
|
pointer++;
|
|
}
|
|
} else {
|
|
if (overlap_length2 >= deletion.length / 2 || overlap_length2 >= insertion.length / 2) {
|
|
// Reverse overlap found.
|
|
// Insert an equality and swap and trim the surrounding edits.
|
|
diffs.insert(pointer, Diff(Operation.equal, deletion.substring(0, overlap_length2)));
|
|
diffs[pointer - 1] = Diff(Operation.insert, insertion.substring(0, insertion.length - overlap_length2));
|
|
diffs[pointer + 1] = Diff(Operation.delete, deletion.substring(overlap_length2));
|
|
pointer++;
|
|
}
|
|
}
|
|
pointer++;
|
|
}
|
|
pointer++;
|
|
}
|
|
}
|
|
|
|
/// Look for single edits surrounded on both sides by equalities
|
|
/// which can be shifted sideways to align the edit to a word boundary.
|
|
/// e.g: The c<ins>at c</ins>ame. -> The <ins>cat </ins>came.
|
|
/// [diffs] is a List of Diff objects.
|
|
void _diff_cleanupSemanticLossless(List<Diff> diffs) {
|
|
/// Given two strings, compute a score representing whether the internal
|
|
/// boundary falls on logical boundaries.
|
|
/// Scores range from 6 (best) to 0 (worst).
|
|
/// Closure, but does not reference any external variables.
|
|
/// [one] the first string.
|
|
/// [two] the second string.
|
|
/// Returns the score.
|
|
int _diff_cleanupSemanticScore(String one, String two) {
|
|
if (one.isEmpty || two.isEmpty) {
|
|
// Edges are the best.
|
|
return 6;
|
|
}
|
|
|
|
// Each port of this function behaves slightly differently due to
|
|
// subtle differences in each language's definition of things like
|
|
// 'whitespace'. Since this function's purpose is largely cosmetic,
|
|
// the choice has been made to use each language's native features
|
|
// rather than force total conformity.
|
|
String char1 = one[one.length - 1];
|
|
String char2 = two[0];
|
|
bool nonAlphaNumeric1 = char1.contains(nonAlphaNumericRegex_);
|
|
bool nonAlphaNumeric2 = char2.contains(nonAlphaNumericRegex_);
|
|
bool whitespace1 = nonAlphaNumeric1 && char1.contains(whitespaceRegex_);
|
|
bool whitespace2 = nonAlphaNumeric2 && char2.contains(whitespaceRegex_);
|
|
bool lineBreak1 = whitespace1 && char1.contains(linebreakRegex_);
|
|
bool lineBreak2 = whitespace2 && char2.contains(linebreakRegex_);
|
|
bool blankLine1 = lineBreak1 && one.contains(blanklineEndRegex_);
|
|
bool blankLine2 = lineBreak2 && two.contains(blanklineStartRegex_);
|
|
|
|
if (blankLine1 || blankLine2) {
|
|
// Five points for blank lines.
|
|
return 5;
|
|
} else if (lineBreak1 || lineBreak2) {
|
|
// Four points for line breaks.
|
|
return 4;
|
|
} else if (nonAlphaNumeric1 && !whitespace1 && whitespace2) {
|
|
// Three points for end of sentences.
|
|
return 3;
|
|
} else if (whitespace1 || whitespace2) {
|
|
// Two points for whitespace.
|
|
return 2;
|
|
} else if (nonAlphaNumeric1 || nonAlphaNumeric2) {
|
|
// One point for non-alphanumeric.
|
|
return 1;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
int pointer = 1;
|
|
// Intentionally ignore the first and last element (don't need checking).
|
|
while (pointer < diffs.length - 1) {
|
|
if (diffs[pointer - 1].operation == Operation.equal && diffs[pointer + 1].operation == Operation.equal) {
|
|
// This is a single edit surrounded by equalities.
|
|
String equality1 = diffs[pointer - 1].text;
|
|
String edit = diffs[pointer].text;
|
|
String equality2 = diffs[pointer + 1].text;
|
|
|
|
// First, shift the edit as far left as possible.
|
|
int commonOffset = diff_commonSuffix(equality1, edit);
|
|
if (commonOffset != 0) {
|
|
String commonString = edit.substring(edit.length - commonOffset);
|
|
equality1 = equality1.substring(0, equality1.length - commonOffset);
|
|
edit = commonString + edit.substring(0, edit.length - commonOffset);
|
|
equality2 = commonString + equality2;
|
|
}
|
|
|
|
// Second, step character by character right, looking for the best fit.
|
|
String bestEquality1 = equality1;
|
|
String bestEdit = edit;
|
|
String bestEquality2 = equality2;
|
|
int bestScore = _diff_cleanupSemanticScore(equality1, edit) + _diff_cleanupSemanticScore(edit, equality2);
|
|
while (edit.isNotEmpty && equality2.isNotEmpty && edit[0] == equality2[0]) {
|
|
equality1 = equality1 + edit[0];
|
|
edit = edit.substring(1) + equality2[0];
|
|
equality2 = equality2.substring(1);
|
|
int score = _diff_cleanupSemanticScore(equality1, edit) + _diff_cleanupSemanticScore(edit, equality2);
|
|
// The >= encourages trailing rather than leading whitespace on edits.
|
|
if (score >= bestScore) {
|
|
bestScore = score;
|
|
bestEquality1 = equality1;
|
|
bestEdit = edit;
|
|
bestEquality2 = equality2;
|
|
}
|
|
}
|
|
|
|
if (diffs[pointer - 1].text != bestEquality1) {
|
|
// We have an improvement, save it back to the diff.
|
|
if (bestEquality1.isNotEmpty) {
|
|
diffs[pointer - 1].text = bestEquality1;
|
|
} else {
|
|
diffs.removeAt(pointer - 1);
|
|
pointer--;
|
|
}
|
|
diffs[pointer].text = bestEdit;
|
|
if (bestEquality2.isNotEmpty) {
|
|
diffs[pointer + 1].text = bestEquality2;
|
|
} else {
|
|
diffs.removeAt(pointer + 1);
|
|
pointer--;
|
|
}
|
|
}
|
|
}
|
|
pointer++;
|
|
}
|
|
}
|
|
|
|
/// Hack to allow unit tests to call private method. Do not use.
|
|
void test_diff_cleanupSemanticLossless(List<Diff> diffs) {
|
|
_diff_cleanupSemanticLossless(diffs);
|
|
}
|
|
|
|
// Define some regex patterns for matching boundaries.
|
|
RegExp nonAlphaNumericRegex_ = RegExp(r'[^a-zA-Z0-9]');
|
|
RegExp whitespaceRegex_ = RegExp(r'\s');
|
|
RegExp linebreakRegex_ = RegExp(r'[\r\n]');
|
|
RegExp blanklineEndRegex_ = RegExp(r'\n\r?\n$');
|
|
RegExp blanklineStartRegex_ = RegExp(r'^\r?\n\r?\n');
|
|
|
|
/// Reduce the number of edits by eliminating operationally trivial equalities.
|
|
/// [diffs] is a List of Diff objects.
|
|
void diff_cleanupEfficiency(List<Diff> diffs) {
|
|
bool changes = false;
|
|
// Stack of indices where equalities are found.
|
|
final equalities = <int>[];
|
|
// Always equal to diffs[equalities.last()].text
|
|
String? lastEquality;
|
|
int pointer = 0; // Index of current position.
|
|
// Is there an insertion operation before the last equality.
|
|
bool pre_ins = false;
|
|
// Is there a deletion operation before the last equality.
|
|
bool pre_del = false;
|
|
// Is there an insertion operation after the last equality.
|
|
bool post_ins = false;
|
|
// Is there a deletion operation after the last equality.
|
|
bool post_del = false;
|
|
while (pointer < diffs.length) {
|
|
if (diffs[pointer].operation == Operation.equal) {
|
|
// Equality found.
|
|
if (diffs[pointer].text.length < Diff_EditCost && (post_ins || post_del)) {
|
|
// Candidate found.
|
|
equalities.add(pointer);
|
|
pre_ins = post_ins;
|
|
pre_del = post_del;
|
|
lastEquality = diffs[pointer].text;
|
|
} else {
|
|
// Not a candidate, and can never become one.
|
|
equalities.clear();
|
|
lastEquality = null;
|
|
}
|
|
post_ins = post_del = false;
|
|
} else {
|
|
// An insertion or deletion.
|
|
if (diffs[pointer].operation == Operation.delete) {
|
|
post_del = true;
|
|
} else {
|
|
post_ins = true;
|
|
}
|
|
/*
|
|
* Five types to be split:
|
|
* <ins>A</ins><del>B</del>XY<ins>C</ins><del>D</del>
|
|
* <ins>A</ins>X<ins>C</ins><del>D</del>
|
|
* <ins>A</ins><del>B</del>X<ins>C</ins>
|
|
* <ins>A</del>X<ins>C</ins><del>D</del>
|
|
* <ins>A</ins><del>B</del>X<del>C</del>
|
|
*/
|
|
if (lastEquality != null && ((pre_ins && pre_del && post_ins && post_del) || ((lastEquality.length < Diff_EditCost / 2) && ((pre_ins ? 1 : 0) + (pre_del ? 1 : 0) + (post_ins ? 1 : 0) + (post_del ? 1 : 0)) == 3))) {
|
|
// Duplicate record.
|
|
diffs.insert(equalities.last, Diff(Operation.delete, lastEquality));
|
|
// Change second copy to insert.
|
|
diffs[equalities.last + 1].operation = Operation.insert;
|
|
equalities.removeLast(); // Throw away the equality we just deleted.
|
|
lastEquality = null;
|
|
if (pre_ins && pre_del) {
|
|
// No changes made which could affect previous entry, keep going.
|
|
post_ins = post_del = true;
|
|
equalities.clear();
|
|
} else {
|
|
if (equalities.isNotEmpty) {
|
|
equalities.removeLast();
|
|
}
|
|
pointer = equalities.isEmpty ? -1 : equalities.last;
|
|
post_ins = post_del = false;
|
|
}
|
|
changes = true;
|
|
}
|
|
}
|
|
pointer++;
|
|
}
|
|
|
|
if (changes) {
|
|
diff_cleanupMerge(diffs);
|
|
}
|
|
}
|
|
|
|
/// Reorder and merge like edit sections. Merge equalities.
|
|
/// Any edit section can move as long as it doesn't cross an equality.
|
|
/// [diffs] is a List of Diff objects.
|
|
void diff_cleanupMerge(List<Diff> diffs) {
|
|
diffs.add(Diff(Operation.equal, '')); // Add a dummy entry at the end.
|
|
int pointer = 0;
|
|
int count_delete = 0;
|
|
int count_insert = 0;
|
|
String text_delete = '';
|
|
String text_insert = '';
|
|
int commonlength;
|
|
while (pointer < diffs.length) {
|
|
switch (diffs[pointer].operation) {
|
|
case Operation.insert:
|
|
count_insert++;
|
|
text_insert += diffs[pointer].text;
|
|
pointer++;
|
|
case Operation.delete:
|
|
count_delete++;
|
|
text_delete += diffs[pointer].text;
|
|
pointer++;
|
|
case Operation.equal:
|
|
// Upon reaching an equality, check for prior redundancies.
|
|
if (count_delete + count_insert > 1) {
|
|
if (count_delete != 0 && count_insert != 0) {
|
|
// Factor out any common prefixies.
|
|
commonlength = diff_commonPrefix(text_insert, text_delete);
|
|
if (commonlength != 0) {
|
|
if ((pointer - count_delete - count_insert) > 0 && diffs[pointer - count_delete - count_insert - 1].operation == Operation.equal) {
|
|
final i = pointer - count_delete - count_insert - 1;
|
|
diffs[i].text = diffs[i].text + text_insert.substring(0, commonlength);
|
|
} else {
|
|
diffs.insert(0, Diff(Operation.equal, text_insert.substring(0, commonlength)));
|
|
pointer++;
|
|
}
|
|
text_insert = text_insert.substring(commonlength);
|
|
text_delete = text_delete.substring(commonlength);
|
|
}
|
|
|
|
// Factor out any common suffixies.
|
|
commonlength = diff_commonSuffix(text_insert, text_delete);
|
|
if (commonlength != 0) {
|
|
diffs[pointer].text = text_insert.substring(text_insert.length - commonlength) + diffs[pointer].text;
|
|
text_insert = text_insert.substring(0, text_insert.length - commonlength);
|
|
text_delete = text_delete.substring(0, text_delete.length - commonlength);
|
|
}
|
|
}
|
|
// Delete the offending records and add the merged ones.
|
|
pointer -= count_delete + count_insert;
|
|
diffs.removeRange(pointer, pointer + count_delete + count_insert);
|
|
if (text_delete.isNotEmpty) {
|
|
diffs.insert(pointer, Diff(Operation.delete, text_delete));
|
|
pointer++;
|
|
}
|
|
if (text_insert.isNotEmpty) {
|
|
diffs.insert(pointer, Diff(Operation.insert, text_insert));
|
|
pointer++;
|
|
}
|
|
pointer++;
|
|
} else if (pointer != 0 && diffs[pointer - 1].operation == Operation.equal) {
|
|
// Merge this equality with the previous one.
|
|
diffs[pointer - 1].text = diffs[pointer - 1].text + diffs[pointer].text;
|
|
diffs.removeAt(pointer);
|
|
} else {
|
|
pointer++;
|
|
}
|
|
count_insert = 0;
|
|
count_delete = 0;
|
|
text_delete = '';
|
|
text_insert = '';
|
|
}
|
|
}
|
|
if (diffs.last.text.isEmpty) {
|
|
diffs.removeLast(); // Remove the dummy entry at the end.
|
|
}
|
|
|
|
// Second pass: look for single edits surrounded on both sides by equalities
|
|
// which can be shifted sideways to eliminate an equality.
|
|
// e.g: A<ins>BA</ins>C -> <ins>AB</ins>AC
|
|
bool changes = false;
|
|
pointer = 1;
|
|
// Intentionally ignore the first and last element (don't need checking).
|
|
while (pointer < diffs.length - 1) {
|
|
if (diffs[pointer - 1].operation == Operation.equal && diffs[pointer + 1].operation == Operation.equal) {
|
|
// This is a single edit surrounded by equalities.
|
|
if (diffs[pointer].text.endsWith(diffs[pointer - 1].text)) {
|
|
// Shift the edit over the previous equality.
|
|
diffs[pointer].text = diffs[pointer - 1].text + diffs[pointer].text.substring(0, diffs[pointer].text.length - diffs[pointer - 1].text.length);
|
|
diffs[pointer + 1].text = diffs[pointer - 1].text + diffs[pointer + 1].text;
|
|
diffs.removeAt(pointer - 1);
|
|
changes = true;
|
|
} else if (diffs[pointer].text.startsWith(diffs[pointer + 1].text)) {
|
|
// Shift the edit over the next equality.
|
|
diffs[pointer - 1].text = diffs[pointer - 1].text + diffs[pointer + 1].text;
|
|
diffs[pointer].text = diffs[pointer].text.substring(diffs[pointer + 1].text.length) + diffs[pointer + 1].text;
|
|
diffs.removeAt(pointer + 1);
|
|
changes = true;
|
|
}
|
|
}
|
|
pointer++;
|
|
}
|
|
// If shifts were made, the diff needs reordering and another shift sweep.
|
|
if (changes) {
|
|
diff_cleanupMerge(diffs);
|
|
}
|
|
}
|
|
|
|
/// loc is a location in text1, compute and return the equivalent location in
|
|
/// text2.
|
|
/// e.g. "The cat" vs "The big cat", 1->1, 5->8
|
|
/// [diffs] is a List of Diff objects.
|
|
/// [loc] is the location within text1.
|
|
/// Returns the location within text2.
|
|
int diff_xIndex(List<Diff> diffs, int loc) {
|
|
int chars1 = 0;
|
|
int chars2 = 0;
|
|
int last_chars1 = 0;
|
|
int last_chars2 = 0;
|
|
Diff? lastDiff;
|
|
for (Diff aDiff in diffs) {
|
|
if (aDiff.operation != Operation.insert) {
|
|
// Equality or deletion.
|
|
chars1 += aDiff.text.length;
|
|
}
|
|
if (aDiff.operation != Operation.delete) {
|
|
// Equality or insertion.
|
|
chars2 += aDiff.text.length;
|
|
}
|
|
if (chars1 > loc) {
|
|
// Overshot the location.
|
|
lastDiff = aDiff;
|
|
break;
|
|
}
|
|
last_chars1 = chars1;
|
|
last_chars2 = chars2;
|
|
}
|
|
if (lastDiff != null && lastDiff.operation == Operation.delete) {
|
|
// The location was deleted.
|
|
return last_chars2;
|
|
}
|
|
// Add the remaining character length.
|
|
return last_chars2 + (loc - last_chars1);
|
|
}
|
|
|
|
/// Convert a Diff list into a pretty HTML report.
|
|
/// [diffs] is a List of Diff objects.
|
|
/// Returns an HTML representation.
|
|
String diff_prettyHtml(List<Diff> diffs) {
|
|
final html = StringBuffer();
|
|
for (Diff aDiff in diffs) {
|
|
String text = aDiff.text.replaceAll('&', '&').replaceAll('<', '<').replaceAll('>', '>').replaceAll('\n', '¶<br>');
|
|
switch (aDiff.operation) {
|
|
case Operation.insert:
|
|
html.write('<ins style="background:#e6ffe6;">');
|
|
html.write(text);
|
|
html.write('</ins>');
|
|
case Operation.delete:
|
|
html.write('<del style="background:#ffe6e6;">');
|
|
html.write(text);
|
|
html.write('</del>');
|
|
case Operation.equal:
|
|
html.write('<span>');
|
|
html.write(text);
|
|
html.write('</span>');
|
|
}
|
|
}
|
|
return html.toString();
|
|
}
|
|
|
|
/// Compute and return the source text (all equalities and deletions).
|
|
/// [diffs] is a List of Diff objects.
|
|
/// Returns the source text.
|
|
String diff_text1(List<Diff> diffs) {
|
|
final text = StringBuffer();
|
|
for (Diff aDiff in diffs) {
|
|
if (aDiff.operation != Operation.insert) {
|
|
text.write(aDiff.text);
|
|
}
|
|
}
|
|
return text.toString();
|
|
}
|
|
|
|
/// Compute and return the destination text (all equalities and insertions).
|
|
/// [diffs] is a List of Diff objects.
|
|
/// Returns the destination text.
|
|
String diff_text2(List<Diff> diffs) {
|
|
final text = StringBuffer();
|
|
for (Diff aDiff in diffs) {
|
|
if (aDiff.operation != Operation.delete) {
|
|
text.write(aDiff.text);
|
|
}
|
|
}
|
|
return text.toString();
|
|
}
|
|
|
|
/// Compute the Levenshtein distance; the number of inserted, deleted or
|
|
/// substituted characters.
|
|
/// [diffs] is a List of Diff objects.
|
|
/// Returns the number of changes.
|
|
int diff_levenshtein(List<Diff> diffs) {
|
|
int levenshtein = 0;
|
|
int insertions = 0;
|
|
int deletions = 0;
|
|
for (Diff aDiff in diffs) {
|
|
switch (aDiff.operation) {
|
|
case Operation.insert:
|
|
insertions += aDiff.text.length;
|
|
case Operation.delete:
|
|
deletions += aDiff.text.length;
|
|
case Operation.equal:
|
|
// A deletion and an insertion is one substitution.
|
|
levenshtein += max(insertions, deletions);
|
|
insertions = 0;
|
|
deletions = 0;
|
|
}
|
|
}
|
|
levenshtein += max(insertions, deletions);
|
|
return levenshtein;
|
|
}
|
|
|
|
/// Crush the diff into an encoded string which describes the operations
|
|
/// required to transform text1 into text2.
|
|
/// E.g. =3\t-2\t+ing -> Keep 3 chars, delete 2 chars, insert 'ing'.
|
|
/// Operations are tab-separated. Inserted text is escaped using %xx notation.
|
|
/// [diffs] is a List of Diff objects.
|
|
/// Returns the delta text.
|
|
String diff_toDelta(List<Diff> diffs) {
|
|
final text = StringBuffer();
|
|
for (Diff aDiff in diffs) {
|
|
switch (aDiff.operation) {
|
|
case Operation.insert:
|
|
text.write('+');
|
|
text.write(Uri.encodeFull(aDiff.text));
|
|
text.write('\t');
|
|
case Operation.delete:
|
|
text.write('-');
|
|
text.write(aDiff.text.length);
|
|
text.write('\t');
|
|
case Operation.equal:
|
|
text.write('=');
|
|
text.write(aDiff.text.length);
|
|
text.write('\t');
|
|
}
|
|
}
|
|
String delta = text.toString();
|
|
if (delta.isNotEmpty) {
|
|
// Strip off trailing tab character.
|
|
delta = delta.substring(0, delta.length - 1);
|
|
}
|
|
return delta.replaceAll('%20', ' ');
|
|
}
|
|
|
|
/// Given the original text1, and an encoded string which describes the
|
|
/// operations required to transform text1 into text2, compute the full diff.
|
|
/// [text1] is the source string for the diff.
|
|
/// [delta] is the delta text.
|
|
/// Returns a List of Diff objects or null if invalid.
|
|
/// Throws ArgumentError if invalid input.
|
|
List<Diff> diff_fromDelta(String text1, String delta) {
|
|
final diffs = <Diff>[];
|
|
int pointer = 0; // Cursor in text1
|
|
final tokens = delta.split('\t');
|
|
for (String token in tokens) {
|
|
if (token.isEmpty) {
|
|
// Blank tokens are ok (from a trailing \t).
|
|
continue;
|
|
}
|
|
// Each token begins with a one character parameter which specifies the
|
|
// operation of this token (delete, insert, equality).
|
|
String param = token.substring(1);
|
|
switch (token[0]) {
|
|
case '+':
|
|
// decode would change all "+" to " "
|
|
param = param.replaceAll('+', '%2B');
|
|
try {
|
|
param = Uri.decodeFull(param);
|
|
} on ArgumentError {
|
|
// Malformed URI sequence.
|
|
throw ArgumentError('Illegal escape in diff_fromDelta: $param');
|
|
}
|
|
diffs.add(Diff(Operation.insert, param));
|
|
case '-':
|
|
// Fall through.
|
|
case '=':
|
|
int n;
|
|
try {
|
|
n = int.parse(param);
|
|
} on FormatException {
|
|
throw ArgumentError('Invalid number in diff_fromDelta: $param');
|
|
}
|
|
if (n < 0) {
|
|
throw ArgumentError('Negative number in diff_fromDelta: $param');
|
|
}
|
|
String text;
|
|
try {
|
|
text = text1.substring(pointer, pointer += n);
|
|
} on RangeError {
|
|
throw ArgumentError('Delta length ($pointer)'
|
|
' larger than source text length (${text1.length}).');
|
|
}
|
|
if (token[0] == '=') {
|
|
diffs.add(Diff(Operation.equal, text));
|
|
} else {
|
|
diffs.add(Diff(Operation.delete, text));
|
|
}
|
|
default:
|
|
// Anything else is an error.
|
|
throw ArgumentError('Invalid diff operation in diff_fromDelta: ${token[0]}');
|
|
}
|
|
}
|
|
if (pointer != text1.length) {
|
|
throw ArgumentError('Delta length ($pointer)'
|
|
' smaller than source text length (${text1.length}).');
|
|
}
|
|
return diffs;
|
|
}
|
|
|
|
// MATCH FUNCTIONS
|
|
|
|
/// Locate the best instance of 'pattern' in 'text' near 'loc'.
|
|
/// Returns -1 if no match found.
|
|
/// [text] is the text to search.
|
|
/// [pattern] is the pattern to search for.
|
|
/// [loc] is the location to search around.
|
|
/// Returns the best match index or -1.
|
|
int match_main(String? text, String? pattern, int loc) {
|
|
// Check for null inputs.
|
|
if (text == null || pattern == null) {
|
|
throw ArgumentError('Null inputs. (match_main)');
|
|
}
|
|
|
|
loc = max(0, min(loc, text.length));
|
|
if (text == pattern) {
|
|
// Shortcut (potentially not guaranteed by the algorithm)
|
|
return 0;
|
|
} else if (text.isEmpty) {
|
|
// Nothing to match.
|
|
return -1;
|
|
} else if (loc + pattern.length <= text.length && text.substring(loc, loc + pattern.length) == pattern) {
|
|
// Perfect match at the perfect spot! (Includes case of null pattern)
|
|
return loc;
|
|
} else {
|
|
// Do a fuzzy compare.
|
|
return _match_bitap(text, pattern, loc);
|
|
}
|
|
}
|
|
|
|
/// Locate the best instance of 'pattern' in 'text' near 'loc' using the
|
|
/// Bitap algorithm. Returns -1 if no match found.
|
|
/// [text] is the the text to search.
|
|
/// [pattern] is the pattern to search for.
|
|
/// [loc] is the location to search around.
|
|
/// Returns the best match index or -1.
|
|
int _match_bitap(String text, String pattern, int loc) {
|
|
if (Match_MaxBits != 0 && pattern.length > Match_MaxBits) {
|
|
throw Exception('Pattern too long for this application.');
|
|
}
|
|
// Initialise the alphabet.
|
|
Map<String, int> s = _match_alphabet(pattern);
|
|
|
|
// Highest score beyond which we give up.
|
|
double score_threshold = Match_Threshold;
|
|
// Is there a nearby exact match? (speedup)
|
|
int best_loc = text.indexOf(pattern, loc);
|
|
if (best_loc != -1) {
|
|
score_threshold = min(_match_bitapScore(0, best_loc, loc, pattern), score_threshold);
|
|
// What about in the other direction? (speedup)
|
|
best_loc = text.lastIndexOf(pattern, loc + pattern.length);
|
|
if (best_loc != -1) {
|
|
score_threshold = min(_match_bitapScore(0, best_loc, loc, pattern), score_threshold);
|
|
}
|
|
}
|
|
|
|
// Initialise the bit arrays.
|
|
final matchmask = 1 << (pattern.length - 1);
|
|
best_loc = -1;
|
|
|
|
int bin_min, bin_mid;
|
|
int bin_max = pattern.length + text.length;
|
|
late List<int> last_rd;
|
|
for (int d = 0; d < pattern.length; d++) {
|
|
// Scan for the best match; each iteration allows for one more error.
|
|
// Run a binary search to determine how far from 'loc' we can stray at
|
|
// this error level.
|
|
bin_min = 0;
|
|
bin_mid = bin_max;
|
|
while (bin_min < bin_mid) {
|
|
if (_match_bitapScore(d, loc + bin_mid, loc, pattern) <= score_threshold) {
|
|
bin_min = bin_mid;
|
|
} else {
|
|
bin_max = bin_mid;
|
|
}
|
|
bin_mid = ((bin_max - bin_min) / 2 + bin_min).toInt();
|
|
}
|
|
// Use the result from this iteration as the maximum for the next.
|
|
bin_max = bin_mid;
|
|
int start = max(1, loc - bin_mid + 1);
|
|
int finish = min(loc + bin_mid, text.length) + pattern.length;
|
|
|
|
final rd = List<int>.filled(finish + 2, -1);
|
|
rd[finish + 1] = (1 << d) - 1;
|
|
for (int j = finish; j >= start; j--) {
|
|
int charMatch;
|
|
if (text.length <= j - 1 || !s.containsKey(text[j - 1])) {
|
|
// Out of range.
|
|
charMatch = 0;
|
|
} else {
|
|
charMatch = s[text[j - 1]]!;
|
|
}
|
|
if (d == 0) {
|
|
// First pass: exact match.
|
|
rd[j] = ((rd[j + 1] << 1) | 1) & charMatch;
|
|
} else {
|
|
// Subsequent passes: fuzzy match.
|
|
rd[j] = ((rd[j + 1] << 1) | 1) & charMatch | (((last_rd[j + 1] | last_rd[j]) << 1) | 1) | last_rd[j + 1];
|
|
}
|
|
if ((rd[j] & matchmask) != 0) {
|
|
double score = _match_bitapScore(d, j - 1, loc, pattern);
|
|
// This match will almost certainly be better than any existing
|
|
// match. But check anyway.
|
|
if (score <= score_threshold) {
|
|
// Told you so.
|
|
score_threshold = score;
|
|
best_loc = j - 1;
|
|
if (best_loc > loc) {
|
|
// When passing loc, don't exceed our current distance from loc.
|
|
start = max(1, 2 * loc - best_loc);
|
|
} else {
|
|
// Already passed loc, downhill from here on in.
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
if (_match_bitapScore(d + 1, loc, loc, pattern) > score_threshold) {
|
|
// No hope for a (better) match at greater error levels.
|
|
break;
|
|
}
|
|
last_rd = rd;
|
|
}
|
|
return best_loc;
|
|
}
|
|
|
|
/// Hack to allow unit tests to call private method. Do not use.
|
|
int test_match_bitap(String text, String pattern, int loc) {
|
|
return _match_bitap(text, pattern, loc);
|
|
}
|
|
|
|
/// Compute and return the score for a match with e errors and x location.
|
|
/// [e] is the number of errors in match.
|
|
/// [x] is the location of match.
|
|
/// [loc] is the expected location of match.
|
|
/// [pattern] is the pattern being sought.
|
|
/// Returns the overall score for match (0.0 = good, 1.0 = bad).
|
|
double _match_bitapScore(int e, int x, int loc, String pattern) {
|
|
final accuracy = e / pattern.length;
|
|
final proximity = (loc - x).abs();
|
|
if (Match_Distance == 0) {
|
|
// Dodge divide by zero error.
|
|
return proximity == 0 ? accuracy : 1.0;
|
|
}
|
|
return accuracy + proximity / Match_Distance;
|
|
}
|
|
|
|
/// Initialise the alphabet for the Bitap algorithm.
|
|
/// [pattern] is the the text to encode.
|
|
/// Returns a Map of character locations.
|
|
Map<String, int> _match_alphabet(String pattern) {
|
|
final s = HashMap<String, int>();
|
|
for (int i = 0; i < pattern.length; i++) {
|
|
s[pattern[i]] = 0;
|
|
}
|
|
for (int i = 0; i < pattern.length; i++) {
|
|
s[pattern[i]] = s[pattern[i]]! | (1 << (pattern.length - i - 1));
|
|
}
|
|
return s;
|
|
}
|
|
|
|
/// Hack to allow unit tests to call private method. Do not use.
|
|
Map<String, int> test_match_alphabet(String pattern) {
|
|
return _match_alphabet(pattern);
|
|
}
|
|
}
|