/*
* 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.IO;
using System.Collections;
using Lucene.Net.Analysis;
using Lucene.Net.Analysis.Tokenattributes;
using Lucene.Net.Util;
namespace Lucene.Net.Analysis.NGram
{
/*
* Tokenizes the input into n-grams of the given size(s).
*/
public sealed class NGramTokenizer : Tokenizer
{
public static int DEFAULT_MIN_NGRAM_SIZE = 1;
public static int DEFAULT_MAX_NGRAM_SIZE = 2;
private int minGram, maxGram;
private int gramSize;
private int pos = 0;
private int inLen;
private string inStr;
private bool started = false;
private ITermAttribute termAtt;
private IOffsetAttribute offsetAtt;
/*
* Creates NGramTokenizer with given min and max n-grams.
* holding the input to be tokenized
* the smallest n-gram to generate
* the largest n-gram to generate
*/
public NGramTokenizer(TextReader input, int minGram, int maxGram)
: base(input)
{
init(minGram, maxGram);
}
/*
* Creates NGramTokenizer with given min and max n-grams.
* to use
* holding the input to be tokenized
* the smallest n-gram to generate
* the largest n-gram to generate
*/
public NGramTokenizer(AttributeSource source, TextReader input, int minGram, int maxGram)
: base(source, input)
{
init(minGram, maxGram);
}
/*
* Creates NGramTokenizer with given min and max n-grams.
* to use
* holding the input to be tokenized
* the smallest n-gram to generate
* the largest n-gram to generate
*/
public NGramTokenizer(AttributeFactory factory, TextReader input, int minGram, int maxGram)
: base(factory, input)
{
init(minGram, maxGram);
}
/*
* Creates NGramTokenizer with default min and max n-grams.
* holding the input to be tokenized
*/
public NGramTokenizer(TextReader input)
: this(input, DEFAULT_MIN_NGRAM_SIZE, DEFAULT_MAX_NGRAM_SIZE)
{
}
private void init(int minGram, int maxGram)
{
if (minGram < 1)
{
throw new System.ArgumentException("minGram must be greater than zero");
}
if (minGram > maxGram)
{
throw new System.ArgumentException("minGram must not be greater than maxGram");
}
this.minGram = minGram;
this.maxGram = maxGram;
this.termAtt = AddAttribute();
this.offsetAtt = AddAttribute();
}
/* Returns the next token in the stream, or null at EOS. */
public override bool IncrementToken()
{
ClearAttributes();
if (!started)
{
started = true;
gramSize = minGram;
char[] chars = new char[1024];
inStr = input.ReadToEnd(); // remove any trailing empty strings
inLen = inStr.Length;
}
if (pos + gramSize > inLen)
{ // if we hit the end of the string
pos = 0; // reset to beginning of string
gramSize++; // increase n-gram size
if (gramSize > maxGram) // we are done
return false;
if (pos + gramSize > inLen)
return false;
}
int oldPos = pos;
pos++;
termAtt.SetTermBuffer(inStr, oldPos, gramSize);
offsetAtt.SetOffset(CorrectOffset(oldPos), CorrectOffset(oldPos + gramSize));
return true;
}
public override void End()
{
// set offset
int finalOffset = inLen;
this.offsetAtt.SetOffset(finalOffset, finalOffset);
}
public override void Reset(TextReader input)
{
base.Reset(input);
Reset();
}
public override void Reset()
{
base.Reset();
started = false;
pos = 0;
}
}
}