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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 chalk.tools.util.featuregen;

import java.util.List;

public class PrefixFeatureGenerator extends FeatureGeneratorAdapter {

  private static final int PREFIX_LENGTH = 4;
  
  public static String[] getPrefixes(String lex) {
    String[] prefs = new String[PREFIX_LENGTH];
    for (int li = 0, ll = PREFIX_LENGTH; li < ll; li++) {
      prefs[li] = lex.substring(0, Math.min(li + 1, lex.length()));
    }
    return prefs;
  }
  
  public void createFeatures(List features, String[] tokens, int index,
      String[] previousOutcomes) {
    String[] prefs = PrefixFeatureGenerator.getPrefixes(tokens[index]);
    for (String pref : prefs) {
      features.add("pre=" + pref);
    }
  }
}