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/*
 * 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.
 * 
 * 

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. * *

Known problem in this implementation: elements that contain themselves tend to * generate events that are harder to serialise as XML. * *

This class is said 'fit' because it will adapt the matrix to the sequences that it * is being given in order to improve performance. * *

Note: The name of this class comes from a contracted version of the features of * this algorithm, as explained below: *

    *
  • Weighted, each token is has a given weight;
  • *
  • Symmetrical, when possible, the algorithm will try to choose a path * that is symmetrical in regards to the arrangement of the tokens;
  • *
  • Matrix, this class uses a matrix for its internal representation;
  • * *
* *

This class is not synchronised. * * @author Christophe Lauret * @version 8 April 2005 */ public final class DiffXFitopsy extends DiffXAlgorithmBase { /** * Set to true 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 DiffXFitopsy(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, 1); // 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))+"\n"); } System.err.println(); 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); // we can only insert or delete, priority to insert if (this.matrix.isGreaterX(i, j)) { // follow the natural path and insert if (this.estate.okInsert(e1)) { if (DEBUG) { System.err.print(" >i +"+ShortStringFormatter.toShortString(e1)); } formatter.insert(e1); this.estate.insert(e1); i++; // if we can format checking at the stack, let's do it } else if (e1.equals(e2) && this.estate.okFormat(e1)) { if (DEBUG) { System.err.print(" d -"+ShortStringFormatter.toShortString(e2)); } formatter.delete(e2); this.estate.delete(e2); j++; } else { if (DEBUG) { System.err.print("\n(i) case greater X"); } if (DEBUG) { printLost(i, j); } break; } // we can only insert or delete, priority to delete } else if (this.matrix.isGreaterY(i, j)) { // follow the natural and delete if (this.estate.okDelete(e2)) { if (DEBUG) { System.err.print(" -->



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