src/Lucene.Net.Core/Analysis/PerFieldAnalyzerWrapper.cs

/* 
 * 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.Collections.Generic;
using Lucene.Net.Support;

namespace Lucene.Net.Analysis
{
    
    /// <summary> This analyzer is used to facilitate scenarios where different
    /// fields require different analysis techniques.  Use <see cref="AddAnalyzer" />
    /// to add a non-default analyzer on a field name basis.
    /// 
    /// <p/>Example usage:
    /// 
    /// <code>
    /// PerFieldAnalyzerWrapper aWrapper =
    /// new PerFieldAnalyzerWrapper(new StandardAnalyzer());
    /// aWrapper.addAnalyzer("firstname", new KeywordAnalyzer());
    /// aWrapper.addAnalyzer("lastname", new KeywordAnalyzer());
    /// </code>
    /// 
    /// <p/>In this example, StandardAnalyzer will be used for all fields except "firstname"
    /// and "lastname", for which KeywordAnalyzer will be used.
    /// 
    /// <p/>A PerFieldAnalyzerWrapper can be used like any other analyzer, for both indexing
    /// and query parsing.
    /// </summary>
    public class PerFieldAnalyzerWrapper:Analyzer
    {
        private readonly Analyzer defaultAnalyzer;
        private readonly IDictionary<string, Analyzer> analyzerMap = new HashMap<string, Analyzer>();
        
        
        /// <summary> Constructs with default analyzer.
        /// 
        /// </summary>
        /// <param name="defaultAnalyzer">Any fields not specifically
        /// defined to use a different analyzer will use the one provided here.
        /// </param>
        public PerFieldAnalyzerWrapper(Analyzer defaultAnalyzer)
            : this(defaultAnalyzer, null)
        {
        }
        
        /// <summary> Constructs with default analyzer and a map of analyzers to use for 
        /// specific fields.
        /// 
        /// </summary>
        /// <param name="defaultAnalyzer">Any fields not specifically
        /// defined to use a different analyzer will use the one provided here.
        /// </param>
        /// <param name="fieldAnalyzers">a Map (String field name to the Analyzer) to be 
        /// used for those fields 
        /// </param>
        public PerFieldAnalyzerWrapper(Analyzer defaultAnalyzer, IEnumerable<KeyValuePair<string, Analyzer>> fieldAnalyzers)
        {
            this.defaultAnalyzer = defaultAnalyzer;
            if (fieldAnalyzers != null)
            {
                foreach(var entry in fieldAnalyzers)
                    analyzerMap[entry.Key] = entry.Value;
            }
            SetOverridesTokenStreamMethod<PerFieldAnalyzerWrapper>();
        }
        
        
        /// <summary> Defines an analyzer to use for the specified field.
        /// 
        /// </summary>
        /// <param name="fieldName">field name requiring a non-default analyzer
        /// </param>
        /// <param name="analyzer">non-default analyzer to use for field
        /// </param>
        public virtual void  AddAnalyzer(System.String fieldName, Analyzer analyzer)
        {
            analyzerMap[fieldName] = analyzer;
        }
        
        public override TokenStream TokenStream(System.String fieldName, System.IO.TextReader reader)
        {
            var analyzer = analyzerMap[fieldName] ?? defaultAnalyzer;

            return analyzer.TokenStream(fieldName, reader);
        }
        
        public override TokenStream ReusableTokenStream(string fieldName, System.IO.TextReader reader)
        {
            if (overridesTokenStreamMethod)
            {
                // LUCENE-1678: force fallback to tokenStream() if we
                // have been subclassed and that subclass overrides
                // tokenStream but not reusableTokenStream
                return TokenStream(fieldName, reader);
            }
            var analyzer = analyzerMap[fieldName] ?? defaultAnalyzer;

            return analyzer.ReusableTokenStream(fieldName, reader);
        }
        
        /// <summary>Return the positionIncrementGap from the analyzer assigned to fieldName </summary>
        public override int GetPositionIncrementGap(string fieldName)
        {
            var analyzer = analyzerMap[fieldName] ?? defaultAnalyzer;
            return analyzer.GetPositionIncrementGap(fieldName);
        }

        /// <summary> Return the offsetGap from the analyzer assigned to field </summary>
        public override int GetOffsetGap(Documents.IFieldable field)
        {
            Analyzer analyzer = analyzerMap[field.Name] ?? defaultAnalyzer;
            return analyzer.GetOffsetGap(field);
        }
        
        public override System.String ToString()
        {
            // {{Aroush-2.9}} will 'analyzerMap.ToString()' work in the same way as Java's java.util.HashMap.toString()? 
            return "PerFieldAnalyzerWrapper(" + analyzerMap + ", default=" + defaultAnalyzer + ")";
        }
    }
}