/*
* 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.sequence;
import java.io.IOException;
import java.util.Iterator;
import com.topologi.diffx.event.DiffXEvent;
import com.topologi.diffx.format.DiffXFormatter;
/**
* The slicer takes two sequences and removes the common elements from the beginning
* and the end of the chain so that only the smallest sequences are passed to the
* DiffXAlgorithmBase.
*
* <p>The slice does modify the original sequences.
*
* <p>Note: Using this class may lead to problems in the execution of the Diff-X
* algorithm and incorrect results, because it could potentially take off some parts
* that helps the Diff-X algorithm ensuring that the XML is well-formed.
*
* @author Christophe Lauret
* @version 6 December 2008
*/
public final class NaiveSequenceSlicer {
// FIXME: symmetrical slicing.
// class attributes ---------------------------------------------------------------------------
/**
* The first sequence of events to test.
*/
final EventSequence sequence1;
/**
* The second sequence of events to test.
*/
final EventSequence sequence2;
/**
* The common start between the two sequences.
*/
EventSequence start;
/**
* The common end between the two sequences.
*/
EventSequence end;
// constructor --------------------------------------------------------------------------------
/**
* Creates a new sequence slicer.
*
* @param seq0 The first sequence to slice.
* @param seq1 The second sequence to slice.
*/
public NaiveSequenceSlicer(EventSequence seq0, EventSequence seq1) {
this.sequence1 = seq0;
this.sequence2 = seq1;
}
// methods ------------------------------------------------------------------------------------
/**
* Slices the start of both sequences.
*
* <p>The common start sequence will be stroed in the class until the next
* {@link #formatStart(DiffXFormatter)} is called.
*
* @return The number of common elements at the start of the sequences.
*
* @throws IllegalStateException If the start buffer is not empty.
*/
public int sliceStart() throws IllegalStateException {
if (this.start != null)
throw new IllegalStateException("The start buffer already contains a subsequence.");
this.start = new EventSequence();
int count = 0;
Iterator<DiffXEvent> i = this.sequence1.eventIterator();
Iterator<DiffXEvent> j = this.sequence2.eventIterator();
while (i.hasNext() && j.hasNext()) {
DiffXEvent e = i.next();
if (j.next().equals(e)) {
count++;
i.remove();
j.remove();
this.start.addEvent(e);
} else return count;
}
return count;
}
/**
* Slices the end of both sequences.
*
* <p>The common end sequence will be stored in the class until the next
* {@link #formatEnd(DiffXFormatter)} is called.
*
* @return The number of common elements at the end of the sequences.
*
* @throws IllegalStateException If the end buffer is not empty.
*/
public int sliceEnd() throws IllegalStateException {
if (this.end != null)
throw new IllegalStateException("The end buffer already contains a subsequence.");
this.end = new EventSequence();
int count = 0;
int pos1 = this.sequence1.size() - 1;
int pos2 = this.sequence2.size() - 1;
while (pos1 >= 0 && pos2 >= 0) {
DiffXEvent e1 = this.sequence1.getEvent(pos1);
if (e1.equals(this.sequence2.getEvent(pos2))) {
count++;
this.sequence1.removeEvent(pos1--);
this.sequence2.removeEvent(pos2--);
this.end.addEvent(0, e1);
} else {
break;
}
}
return count;
}
/**
* Slices the start of both sequences and formats the start subsequence with the specified
* formatter.
*
* <p>Implementation note: although this is functionally equivalent to call successively the
* methods {@link #sliceStart()} and {@link #formatStart(DiffXFormatter)}, this method is
* optimised and passes the event directly to the formatter without using a buffer.
*
* @param formatter The formatter that will handle the output.
*
* @return The number of common elements at the start of the sequences.
*
* @throws IllegalStateException If the start buffer is not empty.
* @throws NullPointerException If the specified formatter is <code>null</code>.
* @throws IOException If an error occurs whilst writing with the formatter.
*/
public int sliceStart(DiffXFormatter formatter)
throws IllegalStateException, NullPointerException, IOException {
if (this.start != null)
throw new IllegalStateException("The start buffer already contains a subsequence.");
int count = 0;
Iterator<DiffXEvent> i = this.sequence1.eventIterator();
Iterator<DiffXEvent> j = this.sequence2.eventIterator();
while (i.hasNext() && j.hasNext()) {
DiffXEvent e = i.next();
if (j.next().equals(e)) {
count++;
i.remove();
j.remove();
formatter.format(e);
} else {
break;
}
}
return count;
}
/**
* Slices the end of both sequences and formats the start subsequence with the specified
* formatter.
*
* <p>Implementation note: although this is exactly equivalent to successive calls to the
* methods {@link #sliceEnd()} and {@link #formatEnd(DiffXFormatter)}.
*
* @param formatter The formatter that will handle the output.
*
* @return The number of common elements at the end of the sequences.
*
* @throws IllegalStateException If the end buffer is not empty.
* @throws NullPointerException If the specified formatter is <code>null</code>.
* @throws IOException If an error occurs whilst writing with the formatter.
*/
public int sliceEnd(DiffXFormatter formatter)
throws IllegalStateException, NullPointerException, IOException {
int count = sliceEnd();
formatEnd(formatter);
return count;
}
/**
* Formats the start subsequence that has been buffered by this class.
*
* <p>This method will clear the buffer, but will do nothing if the start buffer is
* <code>null</code>.
*
* @param formatter The formatter that will handle the output.
*
* @throws NullPointerException If the specified formatter is <code>null</code>.
* @throws IOException If an error occurs whilst writing with the formatter.
*/
public void formatStart(DiffXFormatter formatter) throws NullPointerException, IOException {
if (this.start == null) return;
for (int i = 0; i < this.start.size(); i++) {
formatter.format(this.start.getEvent(i));
}
this.start = null;
}
/**
* Formats the end subsequence that has been buffered by this class.
*
* <p>This method will clear the buffer, but will do nothing if the end buffer is
* <code>null</code>.
*
* @param formatter The formatter that will handle the output.
*
* @throws NullPointerException If the specified formatter is <code>null</code>.
* @throws IOException If an error occurs whilst writing with the formatter.
*/
public void formatEnd(DiffXFormatter formatter) throws NullPointerException, IOException {
if (this.end == null) return;
for (int i = 0; i < this.end.size(); i++) {
formatter.format(this.end.getEvent(i));
}
this.end = null;
}
/**
* Returns the current start sequence buffer.
*
* @return The current start sequence buffer or <code>null</code> if none.
*/
public EventSequence getStart() {
return this.start;
}
/**
* Returns the current end sequence buffer.
*
* @return The current end sequence buffer or <code>null</code> if none.
*/
public EventSequence getEnd() {
return this.end;
}
}