package org.apache.lucene.search;
/**
* Copyright 2006 The Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import java.util.List;
import java.util.Iterator;
import java.io.IOException;
import org.apache.lucene.util.PriorityQueue;
/** A Scorer for OR like queries, counterpart of Lucene's <code>ConjunctionScorer</code>.
* This Scorer implements {@link Scorer#skipTo(int)} and uses skipTo() on the given Scorers.
*/
class DisjunctionSumScorer extends Scorer {
/** The number of subscorers. */
private final int nrScorers;
/** The subscorers. */
protected final List subScorers;
/** The minimum number of scorers that should match. */
private final int minimumNrMatchers;
/** The scorerQueue contains all subscorers ordered by their current doc(),
* with the minimum at the top.
* <br>The scorerQueue is initialized the first time next() or skipTo() is called.
* <br>An exhausted scorer is immediately removed from the scorerQueue.
* <br>If less than the minimumNrMatchers scorers
* remain in the scorerQueue next() and skipTo() return false.
* <p>
* After each to call to next() or skipTo()
* <code>currentSumScore</code> is the total score of the current matching doc,
* <code>nrMatchers</code> is the number of matching scorers,
* and all scorers are after the matching doc, or are exhausted.
*/
private ScorerQueue scorerQueue = null;
/** The document number of the current match. */
private int currentDoc = -1;
/** The number of subscorers that provide the current match. */
protected int nrMatchers = -1;
private float currentScore = Float.NaN;
/** Construct a <code>DisjunctionScorer</code>.
* @param subScorers A collection of at least two subscorers.
* @param minimumNrMatchers The positive minimum number of subscorers that should
* match to match this query.
* <br>When <code>minimumNrMatchers</code> is bigger than
* the number of <code>subScorers</code>,
* no matches will be produced.
* <br>When minimumNrMatchers equals the number of subScorers,
* it more efficient to use <code>ConjunctionScorer</code>.
*/
public DisjunctionSumScorer( List subScorers, int minimumNrMatchers) {
super(null);
nrScorers = subScorers.size();
if (minimumNrMatchers <= 0) {
throw new IllegalArgumentException("Minimum nr of matchers must be positive");
}
if (nrScorers <= 1) {
throw new IllegalArgumentException("There must be at least 2 subScorers");
}
this.minimumNrMatchers = minimumNrMatchers;
this.subScorers = subScorers;
}
/** Construct a <code>DisjunctionScorer</code>, using one as the minimum number
* of matching subscorers.
*/
public DisjunctionSumScorer(List subScorers) {
this(subScorers, 1);
}
/** Called the first time next() or skipTo() is called to
* initialize <code>scorerQueue</code>.
*/
private void initScorerQueue() throws IOException {
Iterator si = subScorers.iterator();
scorerQueue = new ScorerQueue(nrScorers);
while (si.hasNext()) {
Scorer se = (Scorer) si.next();
if (se.next()) { // doc() method will be used in scorerQueue.
scorerQueue.insert(se);
}
}
}
/** A <code>PriorityQueue</code> that orders by {@link Scorer#doc()}. */
private class ScorerQueue extends PriorityQueue {
ScorerQueue(int size) {
initialize(size);
}
protected boolean lessThan(Object o1, Object o2) {
return ((Scorer)o1).doc() < ((Scorer)o2).doc();
}
}
public boolean next() throws IOException {
if (scorerQueue == null) {
initScorerQueue();
}
if (scorerQueue.size() < minimumNrMatchers) {
return false;
} else {
return advanceAfterCurrent();
}
}
/** Advance all subscorers after the current document determined by the
* top of the <code>scorerQueue</code>.
* Repeat until at least the minimum number of subscorers match on the same
* document and all subscorers are after that document or are exhausted.
* <br>On entry the <code>scorerQueue</code> has at least <code>minimumNrMatchers</code>
* available. At least the scorer with the minimum document number will be advanced.
* @return true iff there is a match.
* <br>In case there is a match, </code>currentDoc</code>, </code>currentSumScore</code>,
* and </code>nrMatchers</code> describe the match.
*
* @todo Investigate whether it is possible to use skipTo() when
* the minimum number of matchers is bigger than one, ie. try and use the
* character of ConjunctionScorer for the minimum number of matchers.
*/
protected boolean advanceAfterCurrent() throws IOException {
do { // repeat until minimum nr of matchers
Scorer top = (Scorer) scorerQueue.top();
currentDoc = top.doc();
currentScore = top.score();
nrMatchers = 1;
do { // Until all subscorers are after currentDoc
if (top.next()) {
scorerQueue.adjustTop();
} else {
scorerQueue.pop();
if (scorerQueue.size() < (minimumNrMatchers - nrMatchers)) {
// Not enough subscorers left for a match on this document,
// and also no more chance of any further match.
return false;
}
if (scorerQueue.size() == 0) {
break; // nothing more to advance, check for last match.
}
}
top = (Scorer) scorerQueue.top();
if (top.doc() != currentDoc) {
break; // All remaining subscorers are after currentDoc.
} else {
currentScore += top.score();
nrMatchers++;
}
} while (true);
if (nrMatchers >= minimumNrMatchers) {
return true;
} else if (scorerQueue.size() < minimumNrMatchers) {
return false;
}
} while (true);
}
/** Returns the score of the current document matching the query.
* Initially invalid, until {@link #next()} is called the first time.
*/
public float score() throws IOException { return currentScore; }
public int doc() { return currentDoc; }
/** Returns the number of subscorers matching the current document.
* Initially invalid, until {@link #next()} is called the first time.
*/
public int nrMatchers() {
return nrMatchers;
}
/** Skips to the first match beyond the current whose document number is
* greater than or equal to a given target.
* <br>When this method is used the {@link #explain(int)} method should not be used.
* <br>The implementation uses the skipTo() method on the subscorers.
* @param target The target document number.
* @return true iff there is such a match.
*/
public boolean skipTo(int target) throws IOException {
if (scorerQueue == null) {
initScorerQueue();
}
if (scorerQueue.size() < minimumNrMatchers) {
return false;
}
if (target <= currentDoc) {
return true;
}
do {
Scorer top = (Scorer) scorerQueue.top();
if (top.doc() >= target) {
return advanceAfterCurrent();
} else if (top.skipTo(target)) {
scorerQueue.adjustTop();
} else {
scorerQueue.pop();
if (scorerQueue.size() < minimumNrMatchers) {
return false;
}
}
} while (true);
}
/** Gives and explanation for the score of a given document.
* @todo Show the resulting score. See BooleanScorer.explain() on how to do this.
*/
public Explanation explain(int doc) throws IOException {
Explanation res = new Explanation();
res.setDescription("At least " + minimumNrMatchers + " of");
Iterator ssi = subScorers.iterator();
while (ssi.hasNext()) {
res.addDetail( ((Scorer) ssi.next()).explain(doc));
}
return res;
}
}
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