src/Lucene.Net.Analysis.Phonetic/Language/Caverphone1.cs

// commons-codec version compatibility level: 1.9

namespace Lucene.Net.Analysis.Phonetic.Language
{
    /*
     * 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>
    /// Encodes a string into a Caverphone 1.0 value.
    /// <para/>
    /// This is an algorithm created by the Caversham Project at the University of Otago. It implements the Caverphone 1.0
    /// algorithm:
    /// <para/>
    /// See: <a href="http://en.wikipedia.org/wiki/Caverphone">Wikipedia - Caverphone</a>
    /// <para/>
    /// See: <a href="http://caversham.otago.ac.nz/files/working/ctp060902.pdf">Caverphone 1.0 specification</a>
    /// <para/>
    /// This class is immutable and thread-safe.
    /// <para/>
    /// since 1.5
    /// </summary>
    public class Caverphone1 : AbstractCaverphone
    {
        private const string SIX_1 = "111111";

        /// <summary>
        /// Encodes the given string into a Caverphone value.
        /// </summary>
        /// <param name="source">The source string.</param>
        /// <returns>A caverphone code for the given string.</returns>
        public override string Encode(string source)
        {
            string txt = source;
            if (txt is null || txt.Length == 0)
            {
                return SIX_1;
            }

            // 1. Convert to lowercase
            txt = txt.ToLowerInvariant(); // LUCENENET NOTE: This doesn't work right under "en" language, but does under invariant

            // 2. - 5 - Use pre-compiled regexes for replacements
            foreach (var replacement in REPLACEMENTS)
            {
                txt = replacement.Replace(txt);
            }

            // 6. put ten 1s on the end
            txt = txt + SIX_1;

            // 7. take the first six characters as the code
            return txt.Substring(0, SIX_1.Length - 0);
        }

        private static readonly Replacement[] REPLACEMENTS = new Replacement[]
        {
            // 2. Remove anything not A-Z
            new Replacement("[^a-z]", string.Empty),

            // 3. Handle various start options
            // 2 is a temporary placeholder to indicate a consonant which we are no longer interested in.
            new Replacement("^cough", "cou2f"),
            new Replacement("^rough", "rou2f"),
            new Replacement("^tough", "tou2f"),
            new Replacement("^enough", "enou2f"),
            new Replacement("^gn", "2n"),

            // End
            new Replacement("mb$", "m2"),

            // 4. Handle replacements
            new Replacement("cq", "2q"),
            new Replacement("ci", "si"),
            new Replacement("ce", "se"),
            new Replacement("cy", "sy"),
            new Replacement("tch", "2ch"),
            new Replacement("c", "k"),
            new Replacement("q", "k"),
            new Replacement("x", "k"),
            new Replacement("v", "f"),
            new Replacement("dg", "2g"),
            new Replacement("tio", "sio"),
            new Replacement("tia", "sia"),
            new Replacement("d", "t"),
            new Replacement("ph", "fh"),
            new Replacement("b", "p"),
            new Replacement("sh", "s2"),
            new Replacement("z", "s"),
            new Replacement("^[aeiou]", "A"),
            // 3 is a temporary placeholder marking a vowel
            new Replacement("[aeiou]", "3"),
            new Replacement("3gh3", "3kh3"),
            new Replacement("gh", "22"),
            new Replacement("g", "k"),
            new Replacement("s+", "S"),
            new Replacement("t+", "T"),
            new Replacement("p+", "P"),
            new Replacement("k+", "K"),
            new Replacement("f+", "F"),
            new Replacement("m+", "M"),
            new Replacement("n+", "N"),
            new Replacement("w3", "W3"),
            new Replacement("wy", "Wy"), // 1.0 only
            new Replacement("wh3", "Wh3"),
            new Replacement("why", "Why"), // 1.0 only
            new Replacement("w", "2"),
            new Replacement("^h", "A"),
            new Replacement("h", "2"),
            new Replacement("r3", "R3"),
            new Replacement("ry", "Ry"), // 1.0 only
            new Replacement("r", "2"),
            new Replacement("l3", "L3"),
            new Replacement("ly", "Ly"), // 1.0 only
            new Replacement("l", "2"),
            new Replacement("j", "y"), // 1.0 only
            new Replacement("y3", "Y3"), // 1.0 only
            new Replacement("y", "2"), // 1.0 only

            // 5. Handle removals
            new Replacement("2", string.Empty),
            new Replacement("3", string.Empty),
        };
    }
}