LearnToRankTermScorer.java

package doser.lucene.query;

import java.io.IOException;

import org.apache.lucene.index.DocsEnum;
import org.apache.lucene.search.Scorer;
import org.apache.lucene.search.Weight;
import org.apache.lucene.search.similarities.Similarity;

/**
 * Expert: A <code>Scorer</code> for documents matching a <code>Term</code>.
 */
final class LearnToRankTermScorer extends Scorer {
	private final Similarity.SimScorer docScorer;
	private final DocsEnum docsEnum;

	/**
	 * Construct a <code>TermScorer</code>.
	 * 
	 * @param weight
	 *            The weight of the <code>Term</code> in the query.
	 * @param docsEnum
	 *            An iterator over the documents matching the <code>Term</code>.
	 * @param docScorer
	 *            The </code>Similarity.ExactSimScorer</code> implementation to
	 *            be used for score computations.
	 * @param docFreq
	 *            per-segment docFreq of this term
	 */
	LearnToRankTermScorer(final Weight weight, final DocsEnum docsEnum,
			final Similarity.SimScorer docScorer) {
		super(weight);
		this.docScorer = docScorer;
		this.docsEnum = docsEnum;
	}

	/**
	 * Advances to the first match beyond the current whose document number is
	 * greater than or equal to a given target. <br>
	 * The implementation uses {@link DocsEnum#advance(int)}.
	 * 
	 * @param target
	 *            The target document number.
	 * @return the matching document or NO_MORE_DOCS if none exist.
	 */
	@Override
	public int advance(final int target) throws IOException {
		return docsEnum.advance(target);
	}

	@Override
	public long cost() {
		return docsEnum.cost();
	}

	@Override
	public int docID() {
		return docsEnum.docID();
	}

	@Override
	public int freq() throws IOException {
		return docsEnum.freq();
	}

	DocsEnum getDocsEnum() {
		return docsEnum;
	}

	/**
	 * Advances to the next document matching the query. <br>
	 * 
	 * @return the document matching the query or NO_MORE_DOCS if there are no
	 *         more documents.
	 */
	@Override
	public int nextDoc() throws IOException {
		return docsEnum.nextDoc();
	}

	// TODO: benchmark if the specialized conjunction really benefits
	// from this, or if instead its from sorting by docFreq, or both

	@Override
	public float score() throws IOException {
		assert docID() != NO_MORE_DOCS;
		return docScorer.score(docsEnum.docID(), docsEnum.freq());
	}

	// TODO: generalize something like this for scorers?
	// even this is just an estimation...

	// int getDocFreq() {
	// return docFreq;
	// }

	/** Returns a string representation of this <code>TermScorer</code>. */
	@Override
	public String toString() {
		return "scorer(" + weight + ")";
	}
}