/*
*
* 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 System.IO;
using System.Linq;
using Lucene.Net.Analysis.AR;
using Version = Lucene.Net.Util.Version;
namespace Lucene.Net.Analysis.Fa
{
/*
* {@link Analyzer} for Persian.
*
* This Analyzer uses {@link ArabicLetterTokenizer} which implies tokenizing around
* zero-width non-joiner in addition to whitespace. Some persian-specific variant forms (such as farsi
* yeh and keheh) are standardized. "Stemming" is accomplished via stopwords.
*
*/
public sealed class PersianAnalyzer : Analyzer
{
/*
* File containing default Persian stopwords.
*
* Default stopword list is from
* http://members.unine.ch/jacques.savoy/clef/index.html The stopword list is
* BSD-Licensed.
*
*/
public readonly static String DEFAULT_STOPWORD_FILE = "stopwords.txt";
/*
* Contains the stopwords used with the StopFilter.
*/
private readonly ISet stoptable;
/*
* The comment character in the stopwords file. All lines prefixed with this
* will be ignored
*/
public static readonly String STOPWORDS_COMMENT = "#";
/*
* Returns an unmodifiable instance of the default stop-words set.
* @return an unmodifiable instance of the default stop-words set.
*/
public static ISet getDefaultStopSet()
{
return DefaultSetHolder.DEFAULT_STOP_SET;
}
/*
* Atomically loads the DEFAULT_STOP_SET in a lazy fashion once the outer class
* accesses the static final set the first time.;
*/
private static class DefaultSetHolder
{
internal static readonly ISet DEFAULT_STOP_SET;
static DefaultSetHolder()
{
try
{
DEFAULT_STOP_SET = LoadDefaultStopWordSet();
}
catch (IOException ex)
{
// default set should always be present as it is part of the
// distribution (JAR)
throw new Exception("Unable to load default stopword set");
}
}
static ISet LoadDefaultStopWordSet()
{
var stream = System.Reflection.Assembly.GetAssembly(typeof(PersianAnalyzer)).GetManifestResourceStream("Lucene.Net.Analyzers.Fa." + DEFAULT_STOPWORD_FILE);
try
{
StreamReader reader = new StreamReader(stream, System.Text.Encoding.UTF8);
// make sure it is unmodifiable as we expose it in the outer class
return CharArraySet.UnmodifiableSet(new CharArraySet(WordlistLoader.GetWordSet(reader, STOPWORDS_COMMENT), true));
}
finally
{
stream.Close();
}
}
}
private readonly Version matchVersion;
/*
* Builds an analyzer with the default stop words:
* {@link #DEFAULT_STOPWORD_FILE}.
*/
public PersianAnalyzer(Version matchVersion)
: this(matchVersion, DefaultSetHolder.DEFAULT_STOP_SET)
{
}
/*
* Builds an analyzer with the given stop words
*
* @param matchVersion
* lucene compatibility version
* @param stopwords
* a stopword set
*/
public PersianAnalyzer(Version matchVersion, ISet stopwords)
{
stoptable = CharArraySet.UnmodifiableSet(CharArraySet.Copy(stopwords));
this.matchVersion = matchVersion;
}
/*
* Builds an analyzer with the given stop words.
* @deprecated use {@link #PersianAnalyzer(Version, Set)} instead
*/
public PersianAnalyzer(Version matchVersion, params string[] stopwords)
: this(matchVersion, StopFilter.MakeStopSet(stopwords))
{
}
/*
* Builds an analyzer with the given stop words.
* @deprecated use {@link #PersianAnalyzer(Version, Set)} instead
*/
public PersianAnalyzer(Version matchVersion, IDictionary stopwords)
: this(matchVersion, stopwords.Keys.ToArray())
{
}
/*
* Builds an analyzer with the given stop words. Lines can be commented out
* using {@link #STOPWORDS_COMMENT}
* @deprecated use {@link #PersianAnalyzer(Version, Set)} instead
*/
public PersianAnalyzer(Version matchVersion, FileInfo stopwords)
: this(matchVersion, WordlistLoader.GetWordSet(stopwords, STOPWORDS_COMMENT))
{
}
/*
* Creates a {@link TokenStream} which tokenizes all the text in the provided
* {@link Reader}.
*
* @return A {@link TokenStream} built from a {@link ArabicLetterTokenizer}
* filtered with {@link LowerCaseFilter},
* {@link ArabicNormalizationFilter},
* {@link PersianNormalizationFilter} and Persian Stop words
*/
public override TokenStream TokenStream(String fieldName, TextReader reader)
{
TokenStream result = new ArabicLetterTokenizer(reader);
result = new LowerCaseFilter(result);
result = new ArabicNormalizationFilter(result);
/* additional persian-specific normalization */
result = new PersianNormalizationFilter(result);
/*
* the order here is important: the stopword list is normalized with the
* above!
*/
result = new StopFilter(StopFilter.GetEnablePositionIncrementsVersionDefault(matchVersion),
result, stoptable);
return result;
}
private class SavedStreams
{
protected internal Tokenizer source;
protected internal TokenStream result;
}
/*
* Returns a (possibly reused) {@link TokenStream} which tokenizes all the text
* in the provided {@link Reader}.
*
* @return A {@link TokenStream} built from a {@link ArabicLetterTokenizer}
* filtered with {@link LowerCaseFilter},
* {@link ArabicNormalizationFilter},
* {@link PersianNormalizationFilter} and Persian Stop words
*/
public override TokenStream ReusableTokenStream(String fieldName, TextReader reader)
{
SavedStreams streams = (SavedStreams)PreviousTokenStream;
if (streams == null)
{
streams = new SavedStreams();
streams.source = new ArabicLetterTokenizer(reader);
streams.result = new LowerCaseFilter(streams.source);
streams.result = new ArabicNormalizationFilter(streams.result);
/* additional persian-specific normalization */
streams.result = new PersianNormalizationFilter(streams.result);
/*
* the order here is important: the stopword list is normalized with the
* above!
*/
streams.result = new StopFilter(StopFilter.GetEnablePositionIncrementsVersionDefault(matchVersion),
streams.result, stoptable);
PreviousTokenStream = streams;
}
else
{
streams.source.Reset(reader);
}
return streams.result;
}
}
}