StopFilter.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.
 */

using System;
using System.Collections.Generic;
using Lucene.Net.Analysis.Tokenattributes;
using Lucene.Net.Util;
using QueryParser = Lucene.Net.QueryParsers.QueryParser;
using Version = Lucene.Net.Util.Version;

namespace Lucene.Net.Analysis
{
    
    
    public sealed class StopFilter:TokenFilter
    {
        private readonly CharArraySet stopWords;
        private bool enablePositionIncrements = false;
        
        private readonly ITermAttribute termAtt;
        private readonly IPositionIncrementAttribute posIncrAtt;
        
        public StopFilter(bool enablePositionIncrements, TokenStream input, ISet<string> stopWords, bool ignoreCase)
            : base(input)
        {
            if (stopWords is CharArraySet)
            {
                this.stopWords = (CharArraySet) stopWords;
            }
            else
            {
                this.stopWords = new CharArraySet(stopWords.Count, ignoreCase);
                this.stopWords.AddAll(stopWords);
            }
            this.enablePositionIncrements = enablePositionIncrements;
            termAtt = AddAttribute<ITermAttribute>();
            posIncrAtt = AddAttribute<IPositionIncrementAttribute>();
        }

        public StopFilter(bool enablePositionIncrements, TokenStream @in, ISet<string> stopWords)
            : this(enablePositionIncrements, @in, stopWords, false)
        { }
        
        public static ISet<string> MakeStopSet(params string[] stopWords)
        {
            return MakeStopSet(stopWords, false);
        }
        
        public static ISet<string> MakeStopSet(IList<object> stopWords)
        {
            return MakeStopSet(stopWords, false);
        }
        
        public static ISet<string> MakeStopSet(string[] stopWords, bool ignoreCase)
        {
            var stopSet = new CharArraySet(stopWords.Length, ignoreCase);
            stopSet.AddAll(stopWords);
            return stopSet;
        }
        
        public static ISet<string> MakeStopSet(IList<object> stopWords, bool ignoreCase)
        {
            var stopSet = new CharArraySet(stopWords.Count, ignoreCase);
            foreach(var word in stopWords)
                stopSet.Add(word.ToString());
            return stopSet;
        }
        
        public override bool IncrementToken()
        {
            // return the first non-stop word found
            int skippedPositions = 0;
            while (input.IncrementToken())
            {
                if (!stopWords.Contains(termAtt.TermBuffer(), 0, termAtt.TermLength()))
                {
                    if (enablePositionIncrements)
                    {
                        posIncrAtt.PositionIncrement = posIncrAtt.PositionIncrement + skippedPositions;
                    }
                    return true;
                }
                skippedPositions += posIncrAtt.PositionIncrement;
            }
            // reached EOS -- return false
            return false;
        }
        
        public static bool GetEnablePositionIncrementsVersionDefault(Version matchVersion)
        {
            return matchVersion.OnOrAfter(Version.LUCENE_29);
        }

        public bool EnablePositionIncrements
        {
            get { return enablePositionIncrements; }
            set { enablePositionIncrements = value; }
        }
    }
}