lucene/analysis/common/src/java/org/apache/lucene/analysis/miscellaneous/TypeAsSynonymFilter.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.io.IOException;
import java.util.Set;

import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.FlagsAttribute;
import org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute;
import org.apache.lucene.analysis.tokenattributes.TypeAttribute;
import org.apache.lucene.util.AttributeSource;

/**
 * Adds the {@link TypeAttribute#type()} as a synonym,
 * i.e. another token at the same position, optionally with a specified prefix prepended, optionally
 * transfering flags, and optionally ignoring some types. See {@link TypeAsSynonymFilterFactory} for
 * full details.
 */
public final class TypeAsSynonymFilter extends TokenFilter {
  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
  private final TypeAttribute typeAtt = addAttribute(TypeAttribute.class);
  private final PositionIncrementAttribute posIncrAtt = addAttribute(PositionIncrementAttribute.class);
  private final FlagsAttribute flagsAtt = addAttribute(FlagsAttribute.class);
  private final String prefix;
  private final Set<String> ignore;
  private final int synFlagsMask;

  private AttributeSource.State savedToken = null;


  public TypeAsSynonymFilter(TokenStream input) {
    this(input, null, null, ~0);
  }
  /**
   * @param input input tokenstream
   * @param prefix Prepend this string to every token type emitted as token text.
   *               If null, nothing will be prepended.
   */

  public TypeAsSynonymFilter(TokenStream input, String prefix) {
    this(input, prefix, null, ~0);
  }

  /**
   * @param input  input tokenstream
   * @param prefix Prepend this string to every token type emitted as token text.
   *               If null, nothing will be prepended.
   * @param ignore types to ignore (and not convert to a synonym)
   * @param synFlagsMask a mask to control what flags are propagated to the synonym.
   */
  public TypeAsSynonymFilter(TokenStream input, String prefix, Set<String> ignore, int synFlagsMask) {
    super(input);
    this.prefix = prefix;
    this.ignore = ignore;
    this.synFlagsMask = synFlagsMask;
  }

  @Override
  public boolean incrementToken() throws IOException {
    if (savedToken != null) {         // Emit last token's type at the same position
      restoreState(savedToken);
      savedToken = null;
      termAtt.setEmpty();
      if (prefix != null) {
        termAtt.append(prefix);
      }
      termAtt.append(typeAtt.type());
      posIncrAtt.setPositionIncrement(0);
      // control what flags transfer to synonym
      flagsAtt.setFlags(flagsAtt.getFlags() & synFlagsMask);
      return true;
    } else if (input.incrementToken()) { // No pending token type to emit
      String type = typeAtt.type();
      if (ignore == null || !ignore.contains(type)) {
        savedToken = captureState();
      }
      return true;
    }
    return false;
  }

  @Override
  public void reset() throws IOException {
    super.reset();
    savedToken = null;
  }
}