/*
* Copyright (C) 2009, Christian Halstrick <christian.halstrick@sap.com>
* and other copyright owners as documented in the project's IP log.
*
* This program and the accompanying materials are made available
* under the terms of the Eclipse Distribution License v1.0 which
* accompanies this distribution, is reproduced below, and is
* available at http://www.eclipse.org/org/documents/edl-v10.php
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials provided
* with the distribution.
*
* - Neither the name of the Eclipse Foundation, Inc. nor the
* names of its contributors may be used to endorse or promote
* products derived from this software without specific prior
* written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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package org.eclipse.jgit.merge;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import org.eclipse.jgit.diff.Edit;
import org.eclipse.jgit.diff.EditList;
import org.eclipse.jgit.diff.MyersDiff;
import org.eclipse.jgit.diff.Sequence;
import org.eclipse.jgit.merge.MergeChunk.ConflictState;
/**
* Provides the merge algorithm which does a three-way merge on content provided
* as RawText. Makes use of {@link MyersDiff} to compute the diffs.
*/
public final class MergeAlgorithm {
/**
* Since this class provides only static methods I add a private default
* constructor to prevent instantiation.
*/
private MergeAlgorithm() {
}
// An special edit which acts as a sentinel value by marking the end the
// list of edits
private final static Edit END_EDIT = new Edit(Integer.MAX_VALUE,
Integer.MAX_VALUE);
/**
* Does the three way merge between a common base and two sequences.
*
* @param base the common base sequence
* @param ours the first sequence to be merged
* @param theirs the second sequence to be merged
* @return the resulting content
*/
public static MergeResult merge(Sequence base, Sequence ours,
Sequence theirs) {
List<Sequence> sequences = new ArrayList<Sequence>(3);
sequences.add(base);
sequences.add(ours);
sequences.add(theirs);
MergeResult result = new MergeResult(sequences);
EditList oursEdits = new MyersDiff(base, ours).getEdits();
Iterator<Edit> baseToOurs = oursEdits.iterator();
EditList theirsEdits = new MyersDiff(base, theirs).getEdits();
Iterator<Edit> baseToTheirs = theirsEdits.iterator();
int current = 0; // points to the next line (first line is 0) of base
// which was not handled yet
Edit oursEdit = nextEdit(baseToOurs);
Edit theirsEdit = nextEdit(baseToTheirs);
// iterate over all edits from base to ours and from base to theirs
// leave the loop when there are no edits more for ours or for theirs
// (or both)
while (theirsEdit != END_EDIT || oursEdit != END_EDIT) {
if (oursEdit.getEndA() <= theirsEdit.getBeginA()) {
// something was changed in ours not overlapping with any change
// from theirs. First add the common part in front of the edit
// then the edit.
if (current != oursEdit.getBeginA()) {
result.add(0, current, oursEdit.getBeginA(),
ConflictState.NO_CONFLICT);
}
result.add(1, oursEdit.getBeginB(), oursEdit.getEndB(),
ConflictState.NO_CONFLICT);
current = oursEdit.getEndA();
oursEdit = nextEdit(baseToOurs);
} else if (theirsEdit.getEndA() <= oursEdit.getBeginA()) {
// something was changed in theirs not overlapping with any
// from ours. First add the common part in front of the edit
// then the edit.
if (current != theirsEdit.getBeginA()) {
result.add(0, current, theirsEdit.getBeginA(),
ConflictState.NO_CONFLICT);
}
result.add(2, theirsEdit.getBeginB(), theirsEdit.getEndB(),
ConflictState.NO_CONFLICT);
current = theirsEdit.getEndA();
theirsEdit = nextEdit(baseToTheirs);
} else {
// here we found a real overlapping modification
// if there is a common part in front of the conflict add it
if (oursEdit.getBeginA() != current
&& theirsEdit.getBeginA() != current) {
result.add(0, current, Math.min(oursEdit.getBeginA(),
theirsEdit.getBeginA()), ConflictState.NO_CONFLICT);
}
// set some initial values for the ranges in A and B which we
// want to handle
int oursBeginB = oursEdit.getBeginB();
int theirsBeginB = theirsEdit.getBeginB();
// harmonize the start of the ranges in A and B
if (oursEdit.getBeginA() < theirsEdit.getBeginA()) {
theirsBeginB -= theirsEdit.getBeginA()
- oursEdit.getBeginA();
} else {
oursBeginB -= oursEdit.getBeginA() - theirsEdit.getBeginA();
}
// combine edits:
// Maybe an Edit on one side corresponds to multiple Edits on
// the other side. Then we have to combine the Edits of the
// other side - so in the end we can merge together two single
// edits.
//
// It is important to notice that this combining will extend the
// ranges of our conflict always downwards (towards the end of
// the content). The starts of the conflicting ranges in ours
// and theirs are not touched here.
//
// This combining is an iterative process: after we have
// combined some edits we have to do the check again. The
// combined edits could now correspond to multiple edits on the
// other side.
//
// Example: when this combining algorithm works on the following
// edits
// oursEdits=((0-5,0-5),(6-8,6-8),(10-11,10-11)) and
// theirsEdits=((0-1,0-1),(2-3,2-3),(5-7,5-7))
// it will merge them into
// oursEdits=((0-8,0-8),(10-11,10-11)) and
// theirsEdits=((0-7,0-7))
//
// Since the only interesting thing to us is how in ours and
// theirs the end of the conflicting range is changing we let
// oursEdit and theirsEdit point to the last conflicting edit
Edit nextOursEdit = nextEdit(baseToOurs);
Edit nextTheirsEdit = nextEdit(baseToTheirs);
for (;;) {
if (oursEdit.getEndA() > nextTheirsEdit.getBeginA()) {
theirsEdit = nextTheirsEdit;
nextTheirsEdit = nextEdit(baseToTheirs);
} else if (theirsEdit.getEndA() > nextOursEdit.getBeginA()) {
oursEdit = nextOursEdit;
nextOursEdit = nextEdit(baseToOurs);
} else {
break;
}
}
// harmonize the end of the ranges in A and B
int oursEndB = oursEdit.getEndB();
int theirsEndB = theirsEdit.getEndB();
if (oursEdit.getEndA() < theirsEdit.getEndA()) {
oursEndB += theirsEdit.getEndA() - oursEdit.getEndA();
} else {
theirsEndB += oursEdit.getEndA() - theirsEdit.getEndA();
}
// Add the conflict
result.add(1, oursBeginB, oursEndB,
ConflictState.FIRST_CONFLICTING_RANGE);
result.add(2, theirsBeginB, theirsEndB,
ConflictState.NEXT_CONFLICTING_RANGE);
current = Math.max(oursEdit.getEndA(), theirsEdit.getEndA());
oursEdit = nextOursEdit;
theirsEdit = nextTheirsEdit;
}
}
// maybe we have a common part behind the last edit: copy it to the
// result
if (current < base.size()) {
result.add(0, current, base.size(), ConflictState.NO_CONFLICT);
}
return result;
}
/**
* Helper method which returns the next Edit for an Iterator over Edits.
* When there are no more edits left this method will return the constant
* END_EDIT.
*
* @param it
* the iterator for which the next edit should be returned
* @return the next edit from the iterator or END_EDIT if there no more
* edits
*/
private static Edit nextEdit(Iterator<Edit> it) {
return (it.hasNext() ? it.next() : END_EDIT);
}
}