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The DiffUtils library for computing diffs, applying patches, generationg side-by-side view in Java.
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/*
 * Copyright 2017 java-diff-utils.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.github.difflib.algorithm.jgit;

import com.github.difflib.algorithm.Change;
import com.github.difflib.algorithm.DiffAlgorithmI;
import com.github.difflib.algorithm.DiffAlgorithmListener;
import com.github.difflib.algorithm.DiffException;
import com.github.difflib.patch.DeltaType;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import org.eclipse.jgit.diff.Edit;
import org.eclipse.jgit.diff.EditList;
import org.eclipse.jgit.diff.Sequence;
import org.eclipse.jgit.diff.SequenceComparator;

/**
 * HistorgramDiff using JGit - Library. This one is much more performant than the orginal Myers
 * implementation.
 *
 * @author toben
 */
public class HistogramDiff implements DiffAlgorithmI {

    @Override
    public List computeDiff(List source, List target, DiffAlgorithmListener progress) throws DiffException {
        Objects.requireNonNull(source, "source list must not be null");
        Objects.requireNonNull(target, "target list must not be null");
        if (progress != null) {
            progress.diffStart();
        }
        EditList diffList = new EditList();
        diffList.addAll(new org.eclipse.jgit.diff.HistogramDiff().diff(new DataListComparator<>(progress), new DataList<>(source), new DataList<>(target)));
        List patch = new ArrayList<>();
        for (Edit edit : diffList) {
            DeltaType type = DeltaType.EQUAL;
            switch (edit.getType()) {
                case DELETE:
                    type = DeltaType.DELETE;
                    break;
                case INSERT:
                    type = DeltaType.INSERT;
                    break;
                case REPLACE:
                    type = DeltaType.CHANGE;
                    break;
            }
            patch.add(new Change(type, edit.getBeginA(), edit.getEndA(), edit.getBeginB(), edit.getEndB()));
        }
        if (progress != null) {
            progress.diffEnd();
        }
        return patch;
    }
}

class DataListComparator extends SequenceComparator> {

    private final DiffAlgorithmListener progress;

    public DataListComparator(DiffAlgorithmListener progress) {
        this.progress = progress;
    }

    @Override
    public boolean equals(DataList original, int orgIdx, DataList revised, int revIdx) {
        if (progress != null) {
            progress.diffStep(orgIdx + revIdx, original.size() + revised.size());
        }
        return original.data.get(orgIdx).equals(revised.data.get(revIdx));
    }

    @Override
    public int hash(DataList s, int i) {
        return s.data.get(i).hashCode();
    }

}

class DataList extends Sequence {

    final List data;

    public DataList(List data) {
        this.data = data;
    }

    @Override
    public int size() {
        return data.size();
    }
}