src/Lucene.Net.Analysis.Common/Analysis/De/GermanLightStemmer.cs

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

    /* 
	 * This algorithm is updated based on code located at:
	 * http://members.unine.ch/jacques.savoy/clef/
	 * 
	 * Full copyright for that code follows:
	 */

    /*
	 * Copyright (c) 2005, Jacques Savoy
	 * All rights reserved.
	 *
	 * Redistribution and use in source and binary forms, with or without 
	 * modification, are permitted provided that the following conditions are met:
	 *
	 * Redistributions of source code must retain the above copyright notice, this 
	 * list of conditions and the following disclaimer. Redistributions in binary 
	 * form must reproduce the above copyright notice, this list of conditions and
	 * the following disclaimer in the documentation and/or other materials 
	 * provided with the distribution. Neither the name of the author nor the names 
	 * of its contributors may be used to endorse or promote products derived from 
	 * this software without specific prior written permission.
	 * 
	 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
	 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
	 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
	 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE 
	 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
	 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 
	 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
	 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
	 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
	 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
	 * POSSIBILITY OF SUCH DAMAGE.
	 */

    /// <summary>
    /// Light Stemmer for German.
    /// <para>
    /// This stemmer implements the "UniNE" algorithm in:
    /// <i>Light Stemming Approaches for the French, Portuguese, German and Hungarian Languages</i>
    /// Jacques Savoy
    /// </para>
    /// </summary>
    public class GermanLightStemmer
    {

        public virtual int Stem(char[] s, int len)
        {
            for (int i = 0; i < len; i++)
            {
                switch (s[i])
                {
                    case 'ä':
                    case 'à':
                    case 'á':
                    case 'â':
                        s[i] = 'a';
                        break;
                    case 'ö':
                    case 'ò':
                    case 'ó':
                    case 'ô':
                        s[i] = 'o';
                        break;
                    case 'ï':
                    case 'ì':
                    case 'í':
                    case 'î':
                        s[i] = 'i';
                        break;
                    case 'ü':
                    case 'ù':
                    case 'ú':
                    case 'û':
                        s[i] = 'u';
                        break;
                }
            }

            len = Step1(s, len);
            return Step2(s, len);
        }

        private bool StEnding(char ch)
        {
            switch (ch)
            {
                case 'b':
                case 'd':
                case 'f':
                case 'g':
                case 'h':
                case 'k':
                case 'l':
                case 'm':
                case 'n':
                case 't':
                    return true;
                default:
                    return false;
            }
        }

        private int Step1(char[] s, int len)
        {
            if (len > 5 && s[len - 3] == 'e' && s[len - 2] == 'r' && s[len - 1] == 'n')
            {
                return len - 3;
            }

            if (len > 4 && s[len - 2] == 'e')
            {
                switch (s[len - 1])
                {
                    case 'm':
                    case 'n':
                    case 'r':
                    case 's':
                        return len - 2;
                }
            }

            if (len > 3 && s[len - 1] == 'e')
            {
                return len - 1;
            }

            if (len > 3 && s[len - 1] == 's' && StEnding(s[len - 2]))
            {
                return len - 1;
            }

            return len;
        }

        private int Step2(char[] s, int len)
        {
            if (len > 5 && s[len - 3] == 'e' && s[len - 2] == 's' && s[len - 1] == 't')
            {
                return len - 3;
            }

            if (len > 4 && s[len - 2] == 'e' && (s[len - 1] == 'r' || s[len - 1] == 'n'))
            {
                return len - 2;
            }

            if (len > 4 && s[len - 2] == 's' && s[len - 1] == 't' && StEnding(s[len - 3]))
            {
                return len - 2;
            }

            return len;
        }
    }
}