ReverseStringFilter.cs

Go to the documentation of this file.

/*
 *
 * 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.Linq;
using System.Text;
using Lucene.Net.Analysis.Tokenattributes;

namespace Lucene.Net.Analysis.Reverse
{
    /*
     * Reverse token string, for example "country" => "yrtnuoc".
     * <p>
     * If <c>marker</c> is supplied, then tokens will be also prepended by
     * that character. For example, with a marker of &#x5C;u0001, "country" =>
     * "&#x5C;u0001yrtnuoc". This is useful when implementing efficient leading
     * wildcards search.
     * </p>
     */
    public sealed class ReverseStringFilter : TokenFilter
    {

        private ITermAttribute termAtt;
        private readonly char marker;
        private const char NOMARKER = '\uFFFF';

        /*
         * Example marker character: U+0001 (START OF HEADING) 
         */
        public const char START_OF_HEADING_MARKER = '\u0001';

        /*
         * Example marker character: U+001F (INFORMATION SEPARATOR ONE)
         */
        public const char INFORMATION_SEPARATOR_MARKER = '\u001F';

        /*
         * Example marker character: U+EC00 (PRIVATE USE AREA: EC00) 
         */
        public const char PUA_EC00_MARKER = '\uEC00';

        /*
         * Example marker character: U+200F (RIGHT-TO-LEFT MARK)
         */
        public const char RTL_DIRECTION_MARKER = '\u200F';

        /*
         * Create a new ReverseStringFilter that reverses all tokens in the 
         * supplied {@link TokenStream}.
         * <p>
         * The reversed tokens will not be marked. 
         * </p>
         * 
         * @param in {@link TokenStream} to filter
         */
        public ReverseStringFilter(TokenStream _in)
            : this(_in, NOMARKER)
        {

        }

        /*
         * Create a new ReverseStringFilter that reverses and marks all tokens in the
         * supplied {@link TokenStream}.
         * <p>
         * The reversed tokens will be prepended (marked) by the <c>marker</c>
         * character.
         * </p>
         * 
         * @param in {@link TokenStream} to filter
         * @param marker A character used to mark reversed tokens
         */
        public ReverseStringFilter(TokenStream _in, char marker)
            : base(_in)
        {
            this.marker = marker;
            termAtt = AddAttribute<ITermAttribute>();
        }

        public override bool IncrementToken()
        {
            if (input.IncrementToken())
            {
                int len = termAtt.TermLength();
                if (marker != NOMARKER)
                {
                    len++;
                    termAtt.ResizeTermBuffer(len);
                    termAtt.TermBuffer()[len - 1] = marker;
                }
                Reverse(termAtt.TermBuffer(), len);
                termAtt.SetTermLength(len);
                return true;
            }
            else
            {
                return false;
            }
        }

        public static String Reverse(String input)
        {
            char[] charInput = input.ToCharArray();
            Reverse(charInput);
            return new String(charInput);
        }

        public static void Reverse(char[] buffer)
        {
            Reverse(buffer, buffer.Length);
        }

        public static void Reverse(char[] buffer, int len)
        {
            Reverse(buffer, 0, len);
        }

        public static void Reverse(char[] buffer, int start, int len)
        {
            if (len <= 1) return;
            int num = len >> 1;
            for (int i = start; i < (start + num); i++)
            {
                char c = buffer[i];
                buffer[i] = buffer[start * 2 + len - i - 1];
                buffer[start * 2 + len - i - 1] = c;
            }
        }
    }
}