src/Lucene.Net.Analysis.Common/Analysis/It/ItalianAnalyzer.cs

using Lucene.Net.Analysis.Core;
using Lucene.Net.Analysis.Miscellaneous;
using Lucene.Net.Analysis.Snowball;
using Lucene.Net.Analysis.Standard;
using Lucene.Net.Analysis.Util;
using Lucene.Net.Tartarus.Snowball.Ext;
using Lucene.Net.Util;
using System;
using System.IO;
using System.Text;

namespace Lucene.Net.Analysis.It
{
    /*
     * 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.
     */

    /// <summary>
    /// <see cref="Analyzer"/> for Italian.
    /// <para>You must specify the required <see cref="LuceneVersion"/>
    /// compatibility when creating <see cref="ItalianAnalyzer"/>:
    /// <list type="bullet">
    ///     <item><description> As of 3.6, <see cref="ItalianLightStemFilter"/> is used for less aggressive stemming.</description></item>
    ///     <item><description> As of 3.2, <see cref="ElisionFilter"/> with a set of Italian 
    ///        contractions is used by default.</description></item>
    /// </list>
    /// </para>
    /// </summary>
    public sealed class ItalianAnalyzer : StopwordAnalyzerBase
    {
        private readonly CharArraySet stemExclusionSet;

        /// <summary>
        /// File containing default Italian stopwords. </summary>
        public const string DEFAULT_STOPWORD_FILE = "italian_stop.txt";

        private static readonly CharArraySet DEFAULT_ARTICLES = CharArraySet.UnmodifiableSet(new CharArraySet(
#pragma warning disable 612, 618
            LuceneVersion.LUCENE_CURRENT,
#pragma warning restore 612, 618
            new string[] { "c", "l", "all", "dall", "dell", "nell", "sull", "coll", "pell", "gl", "agl",
                "dagl", "degl", "negl", "sugl", "un", "m", "t", "s", "v", "d" }, true));

        /// <summary>
        /// Returns an unmodifiable instance of the default stop words set. </summary>
        /// <returns> default stop words set. </returns>
        public static CharArraySet DefaultStopSet
        {
            get
            {
                return DefaultSetHolder.DEFAULT_STOP_SET;
            }
        }

        /// <summary>
        /// Atomically loads the <see cref="DEFAULT_STOP_SET"/> in a lazy fashion once the outer class 
        /// accesses the static final set the first time.;
        /// </summary>
        private class DefaultSetHolder
        {
            internal static readonly CharArraySet DEFAULT_STOP_SET = LoadDefaultStopSet();

            private static CharArraySet LoadDefaultStopSet() // LUCENENET: Avoid static constructors (see https://github.com/apache/lucenenet/pull/224#issuecomment-469284006)
            {
                try
                {
                    return WordlistLoader.GetSnowballWordSet(
                        IOUtils.GetDecodingReader(typeof(SnowballFilter), DEFAULT_STOPWORD_FILE, Encoding.UTF8),
#pragma warning disable 612, 618
                        LuceneVersion.LUCENE_CURRENT);
#pragma warning restore 612, 618
                }
                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", ex);
                }
            }
        }

        /// <summary>
        /// Builds an analyzer with the default stop words: <see cref="DEFAULT_STOPWORD_FILE"/>.
        /// </summary>
        /// <param name="matchVersion"> lucene compatibility version </param>
        public ItalianAnalyzer(LuceneVersion matchVersion)
            : this(matchVersion, DefaultSetHolder.DEFAULT_STOP_SET)
        {
        }

        /// <summary>
        /// Builds an analyzer with the given stop words.
        /// </summary>
        /// <param name="matchVersion"> lucene compatibility version </param>
        /// <param name="stopwords"> a stopword set </param>
        public ItalianAnalyzer(LuceneVersion matchVersion, CharArraySet stopwords)
            : this(matchVersion, stopwords, CharArraySet.EMPTY_SET)
        {
        }

        /// <summary>
        /// Builds an analyzer with the given stop words. If a non-empty stem exclusion set is
        /// provided this analyzer will add a <see cref="SetKeywordMarkerFilter"/> before
        /// stemming.
        /// </summary>
        /// <param name="matchVersion"> lucene compatibility version </param>
        /// <param name="stopwords"> a stopword set </param>
        /// <param name="stemExclusionSet"> a set of terms not to be stemmed </param>
        public ItalianAnalyzer(LuceneVersion matchVersion, CharArraySet stopwords, CharArraySet stemExclusionSet)
            : base(matchVersion, stopwords)
        {
            this.stemExclusionSet = CharArraySet.UnmodifiableSet(CharArraySet.Copy(matchVersion, stemExclusionSet));
        }

        /// <summary>
        /// Creates a
        /// <see cref="TokenStreamComponents"/>
        /// which tokenizes all the text in the provided <see cref="TextReader"/>.
        /// </summary>
        /// <returns> A
        ///         <see cref="TokenStreamComponents"/>
        ///         built from an <see cref="StandardTokenizer"/> filtered with
        ///         <see cref="StandardFilter"/>, <see cref="ElisionFilter"/>, <see cref="LowerCaseFilter"/>, <see cref="StopFilter"/>,
        ///         <see cref="SetKeywordMarkerFilter"/> if a stem exclusion set is
        ///         provided and <see cref="ItalianLightStemFilter"/>. </returns>
        protected override TokenStreamComponents CreateComponents(string fieldName, TextReader reader)
        {
            Tokenizer source = new StandardTokenizer(m_matchVersion, reader);
            TokenStream result = new StandardFilter(m_matchVersion, source);
#pragma warning disable 612, 618
            if (m_matchVersion.OnOrAfter(LuceneVersion.LUCENE_32))
#pragma warning restore 612, 618
            {
                result = new ElisionFilter(result, DEFAULT_ARTICLES);
            }
            result = new LowerCaseFilter(m_matchVersion, result);
            result = new StopFilter(m_matchVersion, result, m_stopwords);
            if (stemExclusionSet.Count > 0)
            {
                result = new SetKeywordMarkerFilter(result, stemExclusionSet);
            }
#pragma warning disable 612, 618
            if (m_matchVersion.OnOrAfter(LuceneVersion.LUCENE_36))
#pragma warning restore 612, 618
            {
                result = new ItalianLightStemFilter(result);
            }
            else
            {
                result = new SnowballFilter(result, new ItalianStemmer());
            }
            return new TokenStreamComponents(source, result);
        }
    }
}