001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017
018package org.apache.commons.codec.language;
019
020import org.apache.commons.codec.EncoderException;
021import org.apache.commons.codec.StringEncoder;
022
023/**
024 * Encodes a string into a Soundex value. Soundex is an encoding used to relate similar names, but can also be used as a
025 * general purpose scheme to find word with similar phonemes.
026 *
027 * This class is thread-safe.
028 * Although not strictly immutable, the {@link #maxLength} field is not actually used.
029 *
030 * @version $Id: Soundex.html 891688 2013-12-24 20:49:46Z ggregory $
031 */
032public class Soundex implements StringEncoder {
033
034    /**
035     * This is a default mapping of the 26 letters used in US English. A value of <code>0</code> for a letter position
036     * means do not encode.
037     * <p>
038     * (This constant is provided as both an implementation convenience and to allow Javadoc to pick
039     * up the value for the constant values page.)
040     * </p>
041     *
042     * @see #US_ENGLISH_MAPPING
043     */
044    public static final String US_ENGLISH_MAPPING_STRING = "01230120022455012623010202";
045
046    /**
047     * This is a default mapping of the 26 letters used in US English. A value of <code>0</code> for a letter position
048     * means do not encode.
049     *
050     * @see Soundex#Soundex(char[])
051     */
052    private static final char[] US_ENGLISH_MAPPING = US_ENGLISH_MAPPING_STRING.toCharArray();
053
054    /**
055     * An instance of Soundex using the US_ENGLISH_MAPPING mapping.
056     *
057     * @see #US_ENGLISH_MAPPING
058     */
059    public static final Soundex US_ENGLISH = new Soundex();
060
061    /**
062     * The maximum length of a Soundex code - Soundex codes are only four characters by definition.
063     *
064     * @deprecated This feature is not needed since the encoding size must be constant. Will be removed in 2.0.
065     */
066    @Deprecated
067    private int maxLength = 4;
068
069    /**
070     * Every letter of the alphabet is "mapped" to a numerical value. This char array holds the values to which each
071     * letter is mapped. This implementation contains a default map for US_ENGLISH
072     */
073    private final char[] soundexMapping;
074
075    /**
076     * Creates an instance using US_ENGLISH_MAPPING
077     *
078     * @see Soundex#Soundex(char[])
079     * @see Soundex#US_ENGLISH_MAPPING
080     */
081    public Soundex() {
082        this.soundexMapping = US_ENGLISH_MAPPING;
083    }
084
085    /**
086     * Creates a soundex instance using the given mapping. This constructor can be used to provide an internationalized
087     * mapping for a non-Western character set.
088     *
089     * Every letter of the alphabet is "mapped" to a numerical value. This char array holds the values to which each
090     * letter is mapped. This implementation contains a default map for US_ENGLISH
091     *
092     * @param mapping
093     *                  Mapping array to use when finding the corresponding code for a given character
094     */
095    public Soundex(final char[] mapping) {
096        this.soundexMapping = new char[mapping.length];
097        System.arraycopy(mapping, 0, this.soundexMapping, 0, mapping.length);
098    }
099
100    /**
101     * Creates a refined soundex instance using a custom mapping. This constructor can be used to customize the mapping,
102     * and/or possibly provide an internationalized mapping for a non-Western character set.
103     *
104     * @param mapping
105     *            Mapping string to use when finding the corresponding code for a given character
106     * @since 1.4
107     */
108    public Soundex(final String mapping) {
109        this.soundexMapping = mapping.toCharArray();
110    }
111
112    /**
113     * Encodes the Strings and returns the number of characters in the two encoded Strings that are the same. This
114     * return value ranges from 0 through 4: 0 indicates little or no similarity, and 4 indicates strong similarity or
115     * identical values.
116     *
117     * @param s1
118     *                  A String that will be encoded and compared.
119     * @param s2
120     *                  A String that will be encoded and compared.
121     * @return The number of characters in the two encoded Strings that are the same from 0 to 4.
122     *
123     * @see SoundexUtils#difference(StringEncoder,String,String)
124     * @see <a href="http://msdn.microsoft.com/library/default.asp?url=/library/en-us/tsqlref/ts_de-dz_8co5.asp"> MS
125     *          T-SQL DIFFERENCE </a>
126     *
127     * @throws EncoderException
128     *                  if an error occurs encoding one of the strings
129     * @since 1.3
130     */
131    public int difference(final String s1, final String s2) throws EncoderException {
132        return SoundexUtils.difference(this, s1, s2);
133    }
134
135    /**
136     * Encodes an Object using the soundex algorithm. This method is provided in order to satisfy the requirements of
137     * the Encoder interface, and will throw an EncoderException if the supplied object is not of type java.lang.String.
138     *
139     * @param obj
140     *                  Object to encode
141     * @return An object (or type java.lang.String) containing the soundex code which corresponds to the String
142     *             supplied.
143     * @throws EncoderException
144     *                  if the parameter supplied is not of type java.lang.String
145     * @throws IllegalArgumentException
146     *                  if a character is not mapped
147     */
148    @Override
149    public Object encode(final Object obj) throws EncoderException {
150        if (!(obj instanceof String)) {
151            throw new EncoderException("Parameter supplied to Soundex encode is not of type java.lang.String");
152        }
153        return soundex((String) obj);
154    }
155
156    /**
157     * Encodes a String using the soundex algorithm.
158     *
159     * @param str
160     *                  A String object to encode
161     * @return A Soundex code corresponding to the String supplied
162     * @throws IllegalArgumentException
163     *                  if a character is not mapped
164     */
165    @Override
166    public String encode(final String str) {
167        return soundex(str);
168    }
169
170    /**
171     * Used internally by the SoundEx algorithm.
172     *
173     * Consonants from the same code group separated by W or H are treated as one.
174     *
175     * @param str
176     *                  the cleaned working string to encode (in upper case).
177     * @param index
178     *                  the character position to encode
179     * @return Mapping code for a particular character
180     * @throws IllegalArgumentException
181     *                  if the character is not mapped
182     */
183    private char getMappingCode(final String str, final int index) {
184        // map() throws IllegalArgumentException
185        final char mappedChar = this.map(str.charAt(index));
186        // HW rule check
187        if (index > 1 && mappedChar != '0') {
188            final char hwChar = str.charAt(index - 1);
189            if ('H' == hwChar || 'W' == hwChar) {
190                final char preHWChar = str.charAt(index - 2);
191                final char firstCode = this.map(preHWChar);
192                if (firstCode == mappedChar || 'H' == preHWChar || 'W' == preHWChar) {
193                    return 0;
194                }
195            }
196        }
197        return mappedChar;
198    }
199
200    /**
201     * Returns the maxLength. Standard Soundex
202     *
203     * @deprecated This feature is not needed since the encoding size must be constant. Will be removed in 2.0.
204     * @return int
205     */
206    @Deprecated
207    public int getMaxLength() {
208        return this.maxLength;
209    }
210
211    /**
212     * Returns the soundex mapping.
213     *
214     * @return soundexMapping.
215     */
216    private char[] getSoundexMapping() {
217        return this.soundexMapping;
218    }
219
220    /**
221     * Maps the given upper-case character to its Soundex code.
222     *
223     * @param ch
224     *                  An upper-case character.
225     * @return A Soundex code.
226     * @throws IllegalArgumentException
227     *                  Thrown if <code>ch</code> is not mapped.
228     */
229    private char map(final char ch) {
230        final int index = ch - 'A';
231        if (index < 0 || index >= this.getSoundexMapping().length) {
232            throw new IllegalArgumentException("The character is not mapped: " + ch);
233        }
234        return this.getSoundexMapping()[index];
235    }
236
237    /**
238     * Sets the maxLength.
239     *
240     * @deprecated This feature is not needed since the encoding size must be constant. Will be removed in 2.0.
241     * @param maxLength
242     *                  The maxLength to set
243     */
244    @Deprecated
245    public void setMaxLength(final int maxLength) {
246        this.maxLength = maxLength;
247    }
248
249    /**
250     * Retrieves the Soundex code for a given String object.
251     *
252     * @param str
253     *                  String to encode using the Soundex algorithm
254     * @return A soundex code for the String supplied
255     * @throws IllegalArgumentException
256     *                  if a character is not mapped
257     */
258    public String soundex(String str) {
259        if (str == null) {
260            return null;
261        }
262        str = SoundexUtils.clean(str);
263        if (str.length() == 0) {
264            return str;
265        }
266        final char out[] = {'0', '0', '0', '0'};
267        char last, mapped;
268        int incount = 1, count = 1;
269        out[0] = str.charAt(0);
270        // getMappingCode() throws IllegalArgumentException
271        last = getMappingCode(str, 0);
272        while (incount < str.length() && count < out.length) {
273            mapped = getMappingCode(str, incount++);
274            if (mapped != 0) {
275                if (mapped != '0' && mapped != last) {
276                    out[count++] = mapped;
277                }
278                last = mapped;
279            }
280        }
281        return new String(out);
282    }
283
284}