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package org.apache.wicket.util.diff.myers;
import org.apache.wicket.util.diff.Chunk;
import org.apache.wicket.util.diff.Delta;
import org.apache.wicket.util.diff.Diff;
import org.apache.wicket.util.diff.DiffAlgorithm;
import org.apache.wicket.util.diff.DifferentiationFailedException;
import org.apache.wicket.util.diff.Revision;
/**
* A clean-room implementation of <a
* href="http://www.cs.arizona.edu/people/gene/"> Eugene Myers</a> differencing
* algorithm.
* <p>
* See the paper at <a
* href="http://www.cs.arizona.edu/people/gene/PAPERS/diff.ps">
* http://www.cs.arizona.edu/people/gene/PAPERS/diff.ps</a>
*
* @version $Revision: 1.1 $ $Date: 2006/03/12 00:24:21 $
* @author <a href="mailto:juanco@suigeneris.org">Juanco Anez</a>
* @see Delta
* @see Revision
* @see Diff
*/
public class MyersDiff implements DiffAlgorithm
{
/**
* Constructs an instance of the Myers differencing algorithm.
*/
public MyersDiff()
{
}
/**
* {@inheritDoc}
*/
public Revision diff(Object[] orig, Object[] rev)
throws DifferentiationFailedException
{
PathNode path = buildPath(orig, rev);
return buildRevision(path, orig, rev);
}
/**
* Computes the minimum diffpath that expresses de differences between the
* original and revised sequences, according to Gene Myers differencing
* algorithm.
*
* @param orig
* The original sequence.
* @param rev
* The revised sequence.
* @return A minimum {@link PathNode Path} accross the differences graph.
* @throws DifferentiationFailedException
* if a diff path could not be found.
*/
public static PathNode buildPath(Object[] orig, Object[] rev)
throws DifferentiationFailedException
{
if (orig == null)
throw new IllegalArgumentException("original sequence is null");
if (rev == null)
throw new IllegalArgumentException("revised sequence is null");
// these are local constants
final int N = orig.length;
final int M = rev.length;
final int MAX = N + M + 1;
final int size = 1 + 2 * MAX;
final int middle = (size + 1) / 2;
final PathNode diagonal[] = new PathNode[size];
diagonal[middle + 1] = new Snake(0, -1, null);
for (int d = 0; d < MAX; d++)
{
for (int k = -d; k <= d; k += 2)
{
final int kmiddle = middle + k;
final int kplus = kmiddle + 1;
final int kminus = kmiddle - 1;
PathNode prev = null;
int i;
if ((k == -d)
|| (k != d && diagonal[kminus].i < diagonal[kplus].i))
{
i = diagonal[kplus].i;
prev = diagonal[kplus];
}
else
{
i = diagonal[kminus].i + 1;
prev = diagonal[kminus];
}
diagonal[kminus] = null; // no longer used
int j = i - k;
PathNode node = new DiffNode(i, j, prev);
// orig and rev are zero-based
// but the algorithm is one-based
// that's why there's no +1 when indexing the sequences
while (i < N && j < M && orig[i].equals(rev[j]))
{
i++;
j++;
}
if (i > node.i)
node = new Snake(i, j, node);
diagonal[kmiddle] = node;
if (i >= N && j >= M)
{
return diagonal[kmiddle];
}
}
diagonal[middle + d - 1] = null;
}
// According to Myers, this cannot happen
throw new DifferentiationFailedException("could not find a diff path");
}
/**
* Constructs a {@link Revision} from a difference path.
*
* @param path
* The path.
* @param orig
* The original sequence.
* @param rev
* The revised sequence.
* @return A {@link Revision} script corresponding to the path.
* @throws DifferentiationFailedException
* if a {@link Revision} could not be built from the given path.
*/
public static Revision buildRevision(PathNode path, Object[] orig,
Object[] rev)
{
if (path == null)
throw new IllegalArgumentException("path is null");
if (orig == null)
throw new IllegalArgumentException("original sequence is null");
if (rev == null)
throw new IllegalArgumentException("revised sequence is null");
Revision revision = new Revision();
if (path.isSnake())
path = path.prev;
while (path != null && path.prev != null && path.prev.j >= 0)
{
if (path.isSnake())
throw new IllegalStateException(
"bad diffpath: found snake when looking for diff");
int i = path.i;
int j = path.j;
path = path.prev;
int ianchor = path.i;
int janchor = path.j;
Delta delta = Delta.newDelta(new Chunk(orig, ianchor, i - ianchor),
new Chunk(rev, janchor, j - janchor));
revision.insertDelta(delta);
if (path.isSnake())
path = path.prev;
}
return revision;
}
}