lucene/core/src/java/org/apache/lucene/search/spans/SpanWeight.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */
package org.apache.lucene.search.spans;


import java.io.IOException;
import java.util.Map;

import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.index.PostingsEnum;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermStates;
import org.apache.lucene.search.CollectionStatistics;
import org.apache.lucene.search.Explanation;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.LeafSimScorer;
import org.apache.lucene.search.TermStatistics;
import org.apache.lucene.search.Weight;
import org.apache.lucene.search.similarities.Similarity;
import org.apache.lucene.util.ArrayUtil;

/**
 * Expert-only.  Public for use by other weight implementations
 */
public abstract class SpanWeight extends Weight {

  /**
   * Enumeration defining what postings information should be retrieved from the
   * index for a given Spans
   */
  public enum Postings {
    POSITIONS {
      @Override
      public int getRequiredPostings() {
        return PostingsEnum.POSITIONS;
      }
    },
    PAYLOADS {
      @Override
      public int getRequiredPostings() {
        return PostingsEnum.PAYLOADS;
      }
    },
    OFFSETS {
      @Override
      public int getRequiredPostings() {
        return PostingsEnum.PAYLOADS | PostingsEnum.OFFSETS;
      }
    };

    public abstract int getRequiredPostings();

    public Postings atLeast(Postings postings) {
      if (postings.compareTo(this) > 0)
        return postings;
      return this;
    }
  }

  protected final Similarity similarity;
  protected final Similarity.SimScorer simScorer;
  protected final String field;

  /**
   * Create a new SpanWeight
   * @param query the parent query
   * @param searcher the IndexSearcher to query against
   * @param termStates a map of terms to {@link TermStates} for use in building the similarity.  May
   *                     be null if scores are not required
   * @throws IOException on error
   */
  public SpanWeight(SpanQuery query, IndexSearcher searcher, Map<Term, TermStates> termStates, float boost) throws IOException {
    super(query);
    this.field = query.getField();
    this.similarity = searcher.getSimilarity();
    this.simScorer = buildSimWeight(query, searcher, termStates, boost);
  }

  private Similarity.SimScorer buildSimWeight(SpanQuery query, IndexSearcher searcher, Map<Term, TermStates> termStates, float boost) throws IOException {
    if (termStates == null || termStates.size() == 0 || query.getField() == null)
      return null;
    TermStatistics[] termStats = new TermStatistics[termStates.size()];
    int termUpTo = 0;
    for (Term term : termStates.keySet()) {
      TermStatistics termStatistics = searcher.termStatistics(term, termStates.get(term));
      if (termStatistics != null) {
        termStats[termUpTo++] = termStatistics;
      }
    }
    CollectionStatistics collectionStats = searcher.collectionStatistics(query.getField());
    if (termUpTo > 0) {
      return similarity.scorer(boost, collectionStats, ArrayUtil.copyOfSubArray(termStats, 0, termUpTo));
    } else {
      return null; // no terms at all exist, we won't use similarity
    }
  }

  /**
   * Collect all TermStates used by this Weight
   * @param contexts a map to add the TermStates to
   */
  public abstract void extractTermStates(Map<Term, TermStates> contexts);

  /**
   * Expert: Return a Spans object iterating over matches from this Weight
   * @param ctx a LeafReaderContext for this Spans
   * @return a Spans
   * @throws IOException on error
   */
  public abstract Spans getSpans(LeafReaderContext ctx, Postings requiredPostings) throws IOException;

  @Override
  public SpanScorer scorer(LeafReaderContext context) throws IOException {
    final Spans spans = getSpans(context, Postings.POSITIONS);
    if (spans == null) {
      return null;
    }
    final LeafSimScorer docScorer = getSimScorer(context);
    return new SpanScorer(this, spans, docScorer);
  }

  /**
   * Return a LeafSimScorer for this context
   * @param context the LeafReaderContext
   * @return a SimWeight
   * @throws IOException on error
   */
  public LeafSimScorer getSimScorer(LeafReaderContext context) throws IOException {
    return simScorer == null ? null : new LeafSimScorer(simScorer, context.reader(), field, true);
  }

  @Override
  public Explanation explain(LeafReaderContext context, int doc) throws IOException {
    SpanScorer scorer = scorer(context);
    if (scorer != null) {
      int newDoc = scorer.iterator().advance(doc);
      if (newDoc == doc) {
        float freq = scorer.sloppyFreq();
        LeafSimScorer docScorer = new LeafSimScorer(simScorer, context.reader(), field, true);
        Explanation freqExplanation = Explanation.match(freq, "phraseFreq=" + freq);
        Explanation scoreExplanation = docScorer.explain(doc, freqExplanation);
        return Explanation.match(scoreExplanation.getValue(),
            "weight("+getQuery()+" in "+doc+") [" + similarity.getClass().getSimpleName() + "], result of:",
            scoreExplanation);
      }
    }

    return Explanation.noMatch("no matching term");
  }
}