CachingTokenFilter.cs

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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.
 */

namespace Lucene.Net.Analysis
{
    
    public sealed class CachingTokenFilter : TokenFilter
    {
        private System.Collections.Generic.LinkedList<State> cache = null;
        private System.Collections.Generic.IEnumerator<State> iterator = null;
        private State finalState;
        
        public CachingTokenFilter(TokenStream input):base(input)
        {
        }

        public override bool IncrementToken()
        {
            if (cache == null)
            {
                // fill cache lazily
                cache = new System.Collections.Generic.LinkedList<State>();
                FillCache();
                iterator = cache.GetEnumerator();
            }
            
            if (!iterator.MoveNext())
            {
                // the cache is exhausted, return false
                return false;
            }
            // Since the TokenFilter can be reset, the tokens need to be preserved as immutable.
            RestoreState(iterator.Current);
            return true;
        }
        
        public override void  End()
        {
            if (finalState != null)
            {
                RestoreState(finalState);
            }
        }
        
        public override void  Reset()
        {
            if (cache != null)
            {
                iterator = cache.GetEnumerator();
            }
        }
        
        private void  FillCache()
        {
            while (input.IncrementToken())
            {
                cache.AddLast(CaptureState());
            }
            // capture final state
            input.End();
            finalState = CaptureState();
        }
    }
}