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Apache Solr (module: core)
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/*
 * 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.solr.highlight;

import java.util.Objects;
import java.util.regex.Pattern;
import org.apache.lucene.search.highlight.Fragmenter;
import org.apache.lucene.search.highlight.NullFragmenter;
import org.apache.solr.common.params.HighlightParams;
import org.apache.solr.common.params.SolrParams;
import org.apache.solr.common.util.NamedList;

/**
 * {@link org.apache.lucene.search.highlight.Fragmenter} that tries to produce snippets that "look"
 * like a regular expression. solrconfig.xml parameters:
 *
 * 
 *   hl.regex.pattern: regular expression corresponding to "nice" fragments.
 *   
hl.regex.slop: how far the fragmenter can stray from the ideal fragment size.
 *       A slop of 0.2 means that the fragmenter can go over or under by 20%.
 *   
hl.regex.maxAnalyzedChars: how many characters to apply the regular expression
 *       to (independent from the global highlighter setting).
 * 
 *
 * NOTE: the default for maxAnalyzedChars is much lower for this fragmenter. After this
 * limit is exhausted, fragments are produced in the same way as GapFragmenter
 */
public class RegexFragmenter extends HighlightingPluginBase implements SolrFragmenter {
  protected String defaultPatternRaw;
  protected Pattern defaultPattern;

  @Override
  public void init(NamedList args) {
    super.init(args);
    defaultPatternRaw = LuceneRegexFragmenter.DEFAULT_PATTERN_RAW;
    if (defaults != null) {
      defaultPatternRaw =
          defaults.get(HighlightParams.PATTERN, LuceneRegexFragmenter.DEFAULT_PATTERN_RAW);
    }
    defaultPattern = Pattern.compile(defaultPatternRaw);
  }

  @Override
  public Fragmenter getFragmenter(String fieldName, SolrParams params) {
    numRequests.inc();
    params = SolrParams.wrapDefaults(params, defaults);

    int fragsize =
        params.getFieldInt(
            fieldName, HighlightParams.FRAGSIZE, LuceneRegexFragmenter.DEFAULT_FRAGMENT_SIZE);
    int increment =
        params.getFieldInt(
            fieldName, HighlightParams.INCREMENT, LuceneRegexFragmenter.DEFAULT_INCREMENT_GAP);
    float slop =
        params.getFieldFloat(fieldName, HighlightParams.SLOP, LuceneRegexFragmenter.DEFAULT_SLOP);
    int maxchars =
        params.getFieldInt(
            fieldName,
            HighlightParams.MAX_RE_CHARS,
            LuceneRegexFragmenter.DEFAULT_MAX_ANALYZED_CHARS);
    String rawpat =
        params.getFieldParam(
            fieldName, HighlightParams.PATTERN, LuceneRegexFragmenter.DEFAULT_PATTERN_RAW);

    Pattern p =
        Objects.equals(rawpat, defaultPatternRaw) ? defaultPattern : Pattern.compile(rawpat);

    if (fragsize <= 0) {
      return new NullFragmenter();
    }

    return new LuceneRegexFragmenter(fragsize, increment, slop, maxchars, p);
  }

  ///////////////////////////////////////////////////////////////////////
  //////////////////////// SolrInfoMBeans methods ///////////////////////
  ///////////////////////////////////////////////////////////////////////

  @Override
  public String getDescription() {
    return "RegexFragmenter (" + defaultPatternRaw + ")";
  }
}