src/Lucene.Net.Analysis.Common/Collation/CollationAttributeFactory.cs

#if FEATURE_COLLATION
using Icu.Collation;
using Lucene.Net.Collation.TokenAttributes;
using Lucene.Net.Util;
using System.Reflection;

namespace Lucene.Net.Collation
{
    /*
     * 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>
    /// <para>
    ///   Converts each token into its <see cref="System.Globalization.SortKey"/>, and then
    ///   encodes the bytes as an index term.
    /// </para>
    /// <para>
    ///   <strong>WARNING:</strong> Make sure you use exactly the same <see cref="Collator"/> at
    ///   index and query time -- <see cref="System.Globalization.SortKey"/>s are only comparable when produced by
    ///   the same <see cref="Collator"/>.  Since <see cref="RuleBasedCollator"/>s are not
    ///   independently versioned, it is unsafe to search against stored
    ///   <see cref="System.Globalization.SortKey"/>s unless the following are exactly the same (best practice is
    ///   to store this information with the index and check that they remain the
    ///   same at query time):
    /// </para>
    /// <list type="number">
    ///   <item><description>JVM vendor</description></item>
    ///   <item><description>JVM version, including patch version</description></item>
    ///   <item><description>
    ///     The language (and country and variant, if specified) of the Locale
    ///     used when constructing the collator via
    ///     <see cref="Collator.Create(System.Globalization.CultureInfo)"/>.
    ///   </description></item>
    ///   <item><description>
    ///     The collation strength used - see <see cref="Collator.Strength"/>
    ///   </description></item>
    /// </list> 
    /// <para>
    ///   The <c>ICUCollationAttributeFactory</c> in the analysis-icu package 
    ///   uses ICU4J's Collator, which makes its
    ///   version available, thus allowing collation to be versioned independently
    ///   from the JVM.  ICUCollationAttributeFactory is also significantly faster and
    ///   generates significantly shorter keys than CollationAttributeFactory.  See
    ///   <a href="http://site.icu-project.org/charts/collation-icu4j-sun"
    ///   >http://site.icu-project.org/charts/collation-icu4j-sun</a> for key
    ///   generation timing and key length comparisons between ICU4J and
    ///   <see cref="Collator"/> over several languages.
    /// </para>
    /// <para>
    ///   CollationKeys generated by java.text.Collators are not compatible
    ///   with those those generated by ICU Collators.  Specifically, if you use 
    ///   CollationAttributeFactory to generate index terms, do not use
    ///   ICUCollationAttributeFactory on the query side, or vice versa.
    /// </para>
    /// </summary>
    public class CollationAttributeFactory : AttributeSource.AttributeFactory
    {
        private readonly Collator collator;
        private readonly AttributeSource.AttributeFactory @delegate;

        /// <summary>
        /// Create a <see cref="CollationAttributeFactory"/>, using 
        /// <see cref="AttributeSource.AttributeFactory.DEFAULT_ATTRIBUTE_FACTORY"/> as the
        /// factory for all other attributes. </summary>
        /// <param name="collator"> <see cref="System.Globalization.SortKey"/> generator </param>
        public CollationAttributeFactory(Collator collator) 
            : this(AttributeSource.AttributeFactory.DEFAULT_ATTRIBUTE_FACTORY, collator)
        {
        }

        /// <summary>
        /// Create a <see cref="CollationAttributeFactory"/>, using the supplied Attribute Factory 
        /// as the factory for all other attributes. </summary>
        /// <param name="delegate"> Attribute Factory </param>
        /// <param name="collator"> <see cref="System.Globalization.SortKey"/> generator </param>
        public CollationAttributeFactory(AttributeSource.AttributeFactory @delegate, Collator collator)
        {
            this.@delegate = @delegate;
            this.collator = collator;
        }

        public override Attribute CreateAttributeInstance<T>()
        {
            return typeof(T).IsAssignableFrom(typeof(CollatedTermAttributeImpl))
                ? new CollatedTermAttributeImpl(this.collator)
                : this.@delegate.CreateAttributeInstance<T>();
        }
    }
}
#endif