CharTokenizer.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 Lucene.Net.Analysis.Tokenattributes;
using AttributeSource = Lucene.Net.Util.AttributeSource;

namespace Lucene.Net.Analysis
{
    
    /// <summary>An abstract base class for simple, character-oriented tokenizers.</summary>
    public abstract class CharTokenizer:Tokenizer
    {
        protected CharTokenizer(System.IO.TextReader input):base(input)
        {
            offsetAtt = AddAttribute<IOffsetAttribute>();
            termAtt = AddAttribute<ITermAttribute>();
        }

        protected CharTokenizer(AttributeSource source, System.IO.TextReader input):base(source, input)
        {
            offsetAtt = AddAttribute<IOffsetAttribute>();
            termAtt = AddAttribute<ITermAttribute>();
        }

        protected CharTokenizer(AttributeFactory factory, System.IO.TextReader input):base(factory, input)
        {
            offsetAtt = AddAttribute<IOffsetAttribute>();
            termAtt = AddAttribute<ITermAttribute>();
        }
        
        private int offset = 0, bufferIndex = 0, dataLen = 0;
        private const int MAX_WORD_LEN = 255;
        private const int IO_BUFFER_SIZE = 4096;
        private readonly char[] ioBuffer = new char[IO_BUFFER_SIZE];
        
        private readonly ITermAttribute termAtt;
        private readonly IOffsetAttribute offsetAtt;
        
        /// <summary>Returns true iff a character should be included in a token.  This
        /// tokenizer generates as tokens adjacent sequences of characters which
        /// satisfy this predicate.  Characters for which this is false are used to
        /// define token boundaries and are not included in tokens. 
        /// </summary>
        protected internal abstract bool IsTokenChar(char c);
        
        /// <summary>Called on each token character to normalize it before it is added to the
        /// token.  The default implementation does nothing.  Subclasses may use this
        /// to, e.g., lowercase tokens. 
        /// </summary>
        protected internal virtual char Normalize(char c)
        {
            return c;
        }
        
        public override bool IncrementToken()
        {
            ClearAttributes();
            int length = 0;
            int start = bufferIndex;
            char[] buffer = termAtt.TermBuffer();
            while (true)
            {
                
                if (bufferIndex >= dataLen)
                {
                    offset += dataLen;
                    dataLen = input.Read(ioBuffer, 0, ioBuffer.Length);
                    if (dataLen <= 0)
                    {
                        dataLen = 0; // so next offset += dataLen won't decrement offset
                        if (length > 0)
                            break;
                        return false;
                    }
                    bufferIndex = 0;
                }
                
                char c = ioBuffer[bufferIndex++];
                
                if (IsTokenChar(c))
                {
                    // if it's a token char
                    
                    if (length == 0)
                    // start of token
                        start = offset + bufferIndex - 1;
                    else if (length == buffer.Length)
                        buffer = termAtt.ResizeTermBuffer(1 + length);
                    
                    buffer[length++] = Normalize(c); // buffer it, normalized
                    
                    if (length == MAX_WORD_LEN)
                    // buffer overflow!
                        break;
                }
                else if (length > 0)
                // at non-Letter w/ chars
                    break; // return 'em
            }
            
            termAtt.SetTermLength(length);
            offsetAtt.SetOffset(CorrectOffset(start), CorrectOffset(start + length));
            return true;
        }
        
        public override void  End()
        {
            // set final offset
            int finalOffset = CorrectOffset(offset);
            offsetAtt.SetOffset(finalOffset, finalOffset);
        }
        
        public override void  Reset(System.IO.TextReader input)
        {
            base.Reset(input);
            bufferIndex = 0;
            offset = 0;
            dataLen = 0;
        }
    }
}