SpanFirstQuery.java

package org.apache.lucene.search.spans;


/**
 * Copyright 2004 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.io.IOException;
import java.util.Collection;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.search.Explanation;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.Searcher;

/** Matches spans near the beginning of a field. */
public class SpanFirstQuery extends SpanQuery 
{
  private SpanQuery match;
  private int end;

  /** Construct a SpanFirstQuery matching spans in <code>match</code> whose end
   * position is less than or equal to <code>end</code>. */
  public SpanFirstQuery(SpanQuery match, int end) {
    this.match = match;
    this.end = end;
  }

  /** Return the SpanQuery whose matches are filtered. */
  public SpanQuery getMatch() {
    return match;
  }

  /** Return the maximum end position permitted in a match. */
  public int getEnd() {
    return end;
  }

  public String getField() {
    return match.getField();
  }

  public Collection getTerms() {
    return match.getTerms();
  }

  public Query[] getSubQueries() {
    Query[] result = new Query[1];
    result[0] = match;
    return result;
  }

  public Query rewrite(IndexReader reader)
    throws IOException 
  {
    SpanQuery rewrittenMatch = (SpanQuery)match.rewrite(reader);
    if (rewrittenMatch == match)
      return this;
    SpanFirstQuery clone = (SpanFirstQuery)this.clone();
    clone.match = rewrittenMatch;
    return clone;
  }

  public String toString(String field) {
    StringBuffer buffer = new StringBuffer();
    buffer.append("spanFirst(");
    buffer.append(match.toString(field));
    buffer.append(", ");
    buffer.append(end);
    buffer.append(")");
    return buffer.toString();
  }

  public Spans getSpans(final IndexReader reader, final Searcher searcher)
    throws IOException 
  {
    return new Spans() 
    {
      private Spans spans = match.getSpans(reader, searcher);

      public boolean next()
        throws IOException 
      {
        while (spans.next()) { // scan to next match
          if (end() <= end)
            return true;
        }
        return false;
      }

      public boolean skipTo(int target)
        throws IOException 
      {
        if (!spans.skipTo(target))
          return false;

        if (spans.end() <= end) // there is a match
          return true;

        return next(); // scan to next match
      }

      public int doc() {
        return spans.doc();
      }

      public int start() {
        return spans.start();
      }

      public int end() {
        return spans.end();
      }

      public float score() {
        return spans.score() * getBoost();
      }

      public String toString() {
        return "spans(" + SpanFirstQuery.this.toString() + ")";
      }

      public Explanation explain()
        throws IOException 
      {
        if (getBoost() == 1.0f)
          return spans.explain();

        Explanation result = new Explanation(0,
                                             "weight(" + toString() +
                                             "), product of:");

        Explanation boostExpl = new Explanation(getBoost(), "boost");
        result.addDetail(boostExpl);

        Explanation inclExpl = spans.explain();
        result.addDetail(inclExpl);

        result.setValue(boostExpl.getValue() * inclExpl.getValue());
        return result;
      }
    };
  }
}