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Hibernate Search Analyzer Framework based on Apache Solr
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// original code from Apache Solr - ported to work with Lucene 3.x and reformatted to Search coding style
/**
 * 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.analysis;

import java.io.IOException;
import java.io.Reader;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.apache.lucene.analysis.Token;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.solr.common.SolrException;


/**
 * This tokenizer uses regex pattern matching to construct distinct tokens
 * for the input stream.  It takes two arguments:  "pattern" and "group".
 * 
 * 

 * "pattern" is the regular expression.
 * "group" says which group to extract into tokens.
 * 
 * 
 * group=-1 (the default) is equivalent to "split".  In this case, the tokens will
 * be equivalent to the output from (without empty tokens):
 * {@link String#split(java.lang.String)}
 * 
 * 
 * Using group >= 0 selects the matching group as the token.  For example, if you have:

 * 
 *  pattern = \'([^\']+)\'
 *  group = 0
 *  input = aaa 'bbb' 'ccc'
 * 
 * the output will be two tokens: 'bbb' and 'ccc' (including the ' marks).  With the same input
 * but using group=1, the output would be: bbb and ccc (no ' marks)
 * 
 * NOTE: This Tokenizer does not output tokens that are of zero length.
 *
 * @version $Id:$
 * @see PatternTokenizer
 * @since solr1.2
 */
public class PatternTokenizerFactory extends BaseTokenizerFactory {
	public static final String PATTERN = "pattern";
	public static final String GROUP = "group";

	protected Map args;
	protected Pattern pattern;
	protected int group;

	/**
	 * Require a configured pattern
	 */
	@Override
	public void init(Map args) {
		this.args = args;
		String regex = args.get( PATTERN );
		if ( regex == null ) {
			throw new SolrException( SolrException.ErrorCode.SERVER_ERROR, "missing required argument: " + PATTERN );
		}
		int flags = 0; // TODO? -- read flags from config CASE_INSENSITIVE, etc
		pattern = Pattern.compile( regex, flags );

		group = -1;  // use 'split'
		String g = args.get( GROUP );
		if ( g != null ) {
			try {
				group = Integer.parseInt( g );
			}
			catch ( Exception ex ) {
				throw new SolrException( SolrException.ErrorCode.SERVER_ERROR, "invalid group argument: " + g );
			}
		}
	}

	/**
	 * Split the input using configured pattern
	 */
	public Tokenizer create(final Reader in) {
		try {
			return new PatternTokenizer( in, pattern, group );
		}
		catch ( IOException ex ) {
			throw new SolrException( SolrException.ErrorCode.SERVER_ERROR, ex );
		}
	}

	/**
	 * This behaves just like String.split( ), but returns a list of Tokens
	 * rather then an array of strings
	 * NOTE: This method is not used in 1.4.
	 *
	 * @deprecated
	 */
	@Deprecated
	public static List split(Matcher matcher, String input) {
		int index = 0;
		int lastNonEmptySize = Integer.MAX_VALUE;
		ArrayList matchList = new ArrayList();

		// Add segments before each match found
		while ( matcher.find() ) {
			String match = input.subSequence( index, matcher.start() ).toString();
			matchList.add( new Token( match, index, matcher.start() ) );
			index = matcher.end();
			if ( match.length() > 0 ) {
				lastNonEmptySize = matchList.size();
			}
		}

		// If no match is found, return the full string
		if ( index == 0 ) {
			matchList.add( new Token( input, 0, input.length() ) );
		}
		else {
			String match = input.subSequence( index, input.length() ).toString();
			matchList.add( new Token( match, index, input.length() ) );
			if ( match.length() > 0 ) {
				lastNonEmptySize = matchList.size();
			}
		}

		// Don't use trailing empty strings.  This behavior matches String.split();
		if ( lastNonEmptySize < matchList.size() ) {
			return matchList.subList( 0, lastNonEmptySize );
		}
		return matchList;
	}

	/**
	 * Create tokens from the matches in a matcher
	 * NOTE: This method is not used in 1.4.
	 *
	 * @deprecated
	 */
	@Deprecated
	public static List group(Matcher matcher, String input, int group) {
		ArrayList matchList = new ArrayList();
		while ( matcher.find() ) {
			Token t = new Token(
					matcher.group( group ),
					matcher.start( group ),
					matcher.end( group )
			);
			matchList.add( t );
		}
		return matchList;
	}
}