/*
* This file is part of the DiffX library.
*
* For licensing information please see the file license.txt included in the release.
* A copy of this licence can also be found at
* http://www.opensource.org/licenses/artistic-license-2.0.php
*/
package com.topologi.diffx.algorithm;
import java.io.IOException;
import com.topologi.diffx.event.AttributeEvent;
import com.topologi.diffx.event.DiffXEvent;
import com.topologi.diffx.format.DiffXFormatter;
import com.topologi.diffx.format.ShortStringFormatter;
import com.topologi.diffx.sequence.EventSequence;
/**
* Performs the diff comparison using the LCS algorithm.
*
* <p>Implementation note: this algorithm effectively detects the correct changes in the
* sequences, but will not necessarily return events that can be serialised as well-formed
* XML as they stand.
*
* <p>Known problem in this implementation: elements that contain themselves tend to
* generate events that are harder to serialise as XML.
*
* <p>This class is said 'fit' because it will adapt the matrix to the sequences that it
* is being given in order to improve performance.
*
* <p>Note: The name of this class comes from a contracted version of the features of
* this algorithm, as explained below:
* <ul>
* <li><b>We</b>ighted, each token is has a given weight;</li>
* <li><b>Sy</b>mmetrical, when possible, the algorithm will try to choose a path
* that is symmetrical in regards to the arrangement of the tokens;</li>
* <li><b>Ma</b>trix, this class uses a matrix for its internal representation;</li>
* </li>
* </ul>
*
* <p>This class is not synchronised.
*
* @author Christophe Lauret
* @version 7 April 2005
*/
public final class DiffXFitWesyma extends DiffXAlgorithmBase {
/**
* Set to <code>true</code> to show debug info.
*/
private static final boolean DEBUG = false;
// state variables ----------------------------------------------------------------------------
/**
* Matrix storing the paths.
*/
private transient Matrix matrix;
/**
* The state of the elements.
*/
private transient ElementState estate = new ElementState();
// constructor --------------------------------------------------------------------------------
/**
* Creates a new DiffXAlgorithmBase.
*
* @param seq0 The first sequence to compare.
* @param seq1 The second sequence to compare.
*/
public DiffXFitWesyma(EventSequence seq0, EventSequence seq1) {
super(seq0, seq1);
this.matrix = setupMatrix(seq0, seq1);
}
// methods ------------------------------------------------------------------------------------
/**
* Returns the length of the longest common sequence.
*
* @return the length of the longest common sequence.
*/
public int length() {
// case when one of the sequences is empty
if (this.length1 == 0 || this.length2 == 0) {
this.length = 0;
}
// normal case
if (this.length < 0) {
this.matrix.setup(this.length1+1, this.length2+1);
// allocate storage for array L;
for (int i = super.length1; i >= 0; i--) {
for (int j = super.length2; j >= 0; j--) {
// we reach the end of the sequence (fill with 0)
if (i >= super.length1 || j >= super.length2) {
this.matrix.set(i, j, 0);
} else {
// the events are the same
if (this.sequence1.getEvent(i).equals(this.sequence2.getEvent(j))) {
this.matrix.incrementPathBy(i, j, maxWeight(this.sequence1.getEvent(i), this.sequence2.getEvent(j)));
// different events
} else {
this.matrix.incrementByMaxPath(i, j);
}
}
}
}
this.length = this.matrix.get(0, 0);
}
if (DEBUG) {
System.err.println();
for (int i = 0; i < this.sequence1.size(); i++) {
System.err.print(ShortStringFormatter.toShortString(this.sequence1.getEvent(i))+"\t");
}
System.err.println();
for (int i = 0; i < this.sequence2.size(); i++) {
System.err.print(ShortStringFormatter.toShortString(this.sequence2.getEvent(i))+"\t");
}
System.err.println(this.matrix);
}
return this.length;
}
/**
* Writes the diff sequence using the specified formatter.
*
* @param formatter The formatter that will handle the output.
*
* @throws IOException If thrown by the formatter.
*/
public void process(DiffXFormatter formatter) throws IOException {
// handle the case when one of the two sequences is empty
processEmpty(formatter);
if (this.length1 == 0 || this.length2 == 0) return;
// calculate the LCS length to fill the matrix
length();
int i = 0;
int j = 0;
DiffXEvent e1 = this.sequence1.getEvent(i);
DiffXEvent e2 = this.sequence2.getEvent(j);
// start walking the matrix
while (i < super.length1 && j < super.length2) {
e1 = this.sequence1.getEvent(i);
e2 = this.sequence2.getEvent(j);
// both elements are considered equal
if (e1.equals(e2)) {
formatter.format(e1);
this.estate.format(e1);
i++; j++;
// element from i inserted
} else if (this.matrix.isGreaterX(i, j)) {
formatter.insert(e1);
this.estate.insert(e1);
i++;
// element from j deleted
} else if (this.matrix.isGreaterY(i, j)) {
formatter.delete(e2);
this.estate.delete(e2);
j++;
// elements from i inserted and j deleted
// we have to make a choice for where we are going
// by default, we give priority to the insert and then
// determine which path to follow
} else if (this.matrix.isSameXY(i, j)) {
// choose whether to insert or delete first
boolean priorityInsert = true;
// using the open / close element
if (this.estate.matchCurrent(e1)) {
priorityInsert = true;
}
if (this.estate.matchCurrent(e2)) {
priorityInsert = false;
}
// give priority to attributes
if (e1 instanceof AttributeEvent && !(e2 instanceof AttributeEvent)) {
priorityInsert = true;
} else if (e2 instanceof AttributeEvent && !(e1 instanceof AttributeEvent)) {
priorityInsert = false;
}
// apply priority
if (priorityInsert) {
this.estate.insert(e1);
formatter.insert(e1);
i++;
} else {
this.estate.delete(e1);
formatter.delete(e2);
j++;
}
}
}
// finish off the events from the first sequence
while (i < super.length1) {
this.estate.insert(this.sequence1.getEvent(i));
formatter.insert(this.sequence1.getEvent(i));
i++;
}
// finish off the events from the second sequence
while (j < super.length2) {
this.estate.delete(this.sequence2.getEvent(j));
formatter.delete(this.sequence2.getEvent(j));
j++;
}
// free some resources
// matrix.release();
}
// private helpers (probably inlined by the compiler) -----------------------------------
/**
* Writes the diff sequence using the specified formatter when one of
* the sequences is empty.
*
* <p>The result becomes either only insertions (when the second sequence is
* empty) or deletions (when the first sequence is empty).
*
* @param formatter The formatter that will handle the output.
*
* @throws IOException If thrown by the formatter.
*/
private void processEmpty(DiffXFormatter formatter) throws IOException {
// the first sequence is empty, events from the second sequence have been deleted
if (this.length1 == 0) {
for (int i = 0; i < this.length2; i++) {
formatter.delete(this.sequence2.getEvent(i));
}
}
// the second sequence is empty, events from the first sequence have been inserted
if (this.length2 == 0) {
for (int i = 0; i < this.length1; i++) {
formatter.insert(this.sequence1.getEvent(i));
}
}
}
/**
* Determines the most appropriate matrix to use.
*
* <p>Calculates the maximum length of the shortest weighted path if both sequences
* are totally different, which corresponds to the sum of all the events.
*
* @param s1 The first sequence.
* @param s2 The second sequence.
*
* @return The most appropriate matrix.
*/
private static Matrix setupMatrix(EventSequence s1, EventSequence s2) {
int max = 0;
for (int i = 0; i < s1.size(); i++) {
max += s1.getEvent(i).getWeight();
}
for (int i = 0; i < s2.size(); i++) {
max += s2.getEvent(i).getWeight();
}
if (max > Short.MAX_VALUE)
return new MatrixInt();
else
return new MatrixShort();
}
/**
* Returns the max weight of the two events.
*
* @param e1 The first event.
* @param e2 The second event.
*
* @return The weight for the event.
*/
private int maxWeight(DiffXEvent e1, DiffXEvent e2) {
return e1.getWeight() > e2.getWeight()? e1.getWeight() : e2.getWeight();
}
}