lucene/analysis/common/src/java/org/apache/lucene/analysis/miscellaneous/ConcatenateGraphFilterFactory.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.analysis.miscellaneous;

import java.util.Map;

import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.util.TokenFilterFactory;
import org.apache.lucene.util.Version;
import org.apache.lucene.util.automaton.TooComplexToDeterminizeException;

/**
 * Factory for {@link ConcatenateGraphFilter}.
 *
 * <ul>
 *   <li><tt>preserveSep</tt>:
 *                            For lucene versions lesser than {@link org.apache.lucene.util.Version#LUCENE_8_4_0}
 *                            Whether {@link ConcatenateGraphFilter#SEP_LABEL}
 *                            should separate the input tokens in the concatenated token
 *                            </li>
 *   <li><tt>tokenSeparator</tt>:
 *                            Separator to use for concatenation. If not present,
 *                            {@link ConcatenateGraphFilter#DEFAULT_TOKEN_SEPARATOR} will be used.
 *                            If empty, tokens will be concatenated without any separators.
 *                            </li>
 *   <li><tt>preservePositionIncrements</tt>:
 *                                       Whether to add an empty token for missing positions.
 *                                       The effect is a consecutive {@link ConcatenateGraphFilter#SEP_LABEL}.
 *                                       When false, it's as if there were no missing positions
 *                                         (we pretend the surrounding tokens were adjacent).
 *                                       </li>
 *   <li><tt>maxGraphExpansions</tt>:
 *                            If the tokenStream graph has more than this many possible paths through, then we'll throw
 *                            {@link TooComplexToDeterminizeException} to preserve the stability and memory of the
 *                            machine.
 *                            </li>
 * </ul>
 * @see ConcatenateGraphFilter
 * @since 7.4.0
 * @lucene.spi {@value #NAME}
 */
public class ConcatenateGraphFilterFactory extends TokenFilterFactory {

  /** SPI name */
  public static final String NAME = "concatenateGraph";

  private Character tokenSeparator;
  private boolean preservePositionIncrements;
  private int maxGraphExpansions;

  public ConcatenateGraphFilterFactory(Map<String, String> args) {
    super(args);
    Version luceneMatchVersion = getLuceneMatchVersion();
    if (luceneMatchVersion.onOrAfter(Version.LUCENE_8_4_0)) {
      tokenSeparator = getCharacter(args, "tokenSeparator", ConcatenateGraphFilter.DEFAULT_TOKEN_SEPARATOR);
    } else {
      boolean preserveSep = getBoolean(args, "preserveSep", ConcatenateGraphFilter.DEFAULT_PRESERVE_SEP);
      tokenSeparator = (preserveSep) ? ConcatenateGraphFilter.DEFAULT_TOKEN_SEPARATOR : null;
    }
    preservePositionIncrements = getBoolean(args, "preservePositionIncrements", ConcatenateGraphFilter.DEFAULT_PRESERVE_POSITION_INCREMENTS);
    maxGraphExpansions = getInt(args, "maxGraphExpansions", ConcatenateGraphFilter.DEFAULT_MAX_GRAPH_EXPANSIONS);

    if (!args.isEmpty()) {
      throw new IllegalArgumentException("Unknown parameters: " + args);
    }
  }

  @Override
  public TokenStream create(TokenStream input) {
    return new ConcatenateGraphFilter(input, tokenSeparator, preservePositionIncrements, maxGraphExpansions);
  }

  protected Character getCharacter(Map<String,String> args, String name, Character defaultVal) {
    String s = args.remove(name);
    if (s == null) {
      return defaultVal;
    } else if (s.length() == 0) {
      return null;
    } else {
      if (s.length() != 1) {
        throw new IllegalArgumentException(name + " should be a char. \"" + s + "\" is invalid");
      } else {
        return s.charAt(0);
      }
    }
  }
}