package org.apache.lucene.analysis;

/**
 * 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.
 */

import java.io.IOException;
import java.util.LinkedList;
import java.util.List;

/**
 * This class can be used if the Tokens of a TokenStream
 * are intended to be consumed more than once. It caches
 * all Tokens locally in a List.
 * 
 * CachingTokenFilter implements the optional method
 * {@link TokenStream#reset()}, which repositions the
 * stream to the first Token. 
 *
 */
public class CachingTokenFilter extends TokenFilter {
  private List cache;
  private int index;
  
  public CachingTokenFilter(TokenStream input) {
    super(input);
  }
  
  public Token next() throws IOException {
    if (cache == null) {
      // fill cache lazily
      cache = new LinkedList();
      fillCache();
    }
    
    if (index == cache.size()) {
      // the cache is exhausted, return null
      return null;
    }
    
    return (Token) cache.get(index++);
  }
  
  public void reset() throws IOException {
    index = 0;
  }
  
  private void fillCache() throws IOException {
    Token token;
    while ( (token = input.next()) != null) {
      cache.add(token);
    }
  }

}