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 */
017package org.apache.commons.codec.language;
018
019import java.io.InputStream;
020import java.util.ArrayList;
021import java.util.Arrays;
022import java.util.Collections;
023import java.util.Comparator;
024import java.util.HashMap;
025import java.util.LinkedHashSet;
026import java.util.List;
027import java.util.Map;
028import java.util.Scanner;
029import java.util.Set;
030
031import org.apache.commons.codec.CharEncoding;
032import org.apache.commons.codec.EncoderException;
033import org.apache.commons.codec.StringEncoder;
034
035/**
036 * Encodes a string into a Daitch-Mokotoff Soundex value.
037 * <p>
038 * The Daitch-Mokotoff Soundex algorithm is a refinement of the Russel and American Soundex algorithms, yielding greater
039 * accuracy in matching especially Slavish and Yiddish surnames with similar pronunciation but differences in spelling.
040 * </p>
041 * <p>
042 * The main differences compared to the other soundex variants are:
043 * </p>
044 * <ul>
045 * <li>coded names are 6 digits long
046 * <li>the initial character of the name is coded
047 * <li>rules to encoded multi-character n-grams
048 * <li>multiple possible encodings for the same name (branching)
049 * </ul>
050 * <p>
051 * This implementation supports branching, depending on the used method:
052 * <ul>
053 * <li>{@link #encode(String)} - branching disabled, only the first code will be returned
054 * <li>{@link #soundex(String)} - branching enabled, all codes will be returned, separated by '|'
055 * </ul>
056 * <p>
057 * Note: this implementation has additional branching rules compared to the original description of the algorithm. The
058 * rules can be customized by overriding the default rules contained in the resource file
059 * {@code org/apache/commons/codec/language/dmrules.txt}.
060 * </p>
061 * <p>
062 * This class is thread-safe.
063 * </p>
064 *
065 * @see Soundex
066 * @see <a href="http://en.wikipedia.org/wiki/Daitch%E2%80%93Mokotoff_Soundex"> Wikipedia - Daitch-Mokotoff Soundex</a>
067 * @see <a href="http://www.avotaynu.com/soundex.htm">Avotaynu - Soundexing and Genealogy</a>
068 *
069 * @version $Id$
070 * @since 1.10
071 */
072public class DaitchMokotoffSoundex implements StringEncoder {
073
074    /**
075     * Inner class representing a branch during DM soundex encoding.
076     */
077    private static final class Branch {
078        private final StringBuilder builder;
079        private String cachedString;
080        private String lastReplacement;
081
082        private Branch() {
083            builder = new StringBuilder();
084            lastReplacement = null;
085            cachedString = null;
086        }
087
088        /**
089         * Creates a new branch, identical to this branch.
090         *
091         * @return a new, identical branch
092         */
093        public Branch createBranch() {
094            final Branch branch = new Branch();
095            branch.builder.append(toString());
096            branch.lastReplacement = this.lastReplacement;
097            return branch;
098        }
099
100        @Override
101        public boolean equals(final Object other) {
102            if (this == other) {
103                return true;
104            }
105            if (!(other instanceof Branch)) {
106                return false;
107            }
108
109            return toString().equals(((Branch) other).toString());
110        }
111
112        /**
113         * Finish this branch by appending '0's until the maximum code length has been reached.
114         */
115        public void finish() {
116            while (builder.length() < MAX_LENGTH) {
117                builder.append('0');
118                cachedString = null;
119            }
120        }
121
122        @Override
123        public int hashCode() {
124            return toString().hashCode();
125        }
126
127        /**
128         * Process the next replacement to be added to this branch.
129         *
130         * @param replacement
131         *            the next replacement to append
132         * @param forceAppend
133         *            indicates if the default processing shall be overridden
134         */
135        public void processNextReplacement(final String replacement, final boolean forceAppend) {
136            final boolean append = lastReplacement == null || !lastReplacement.endsWith(replacement) || forceAppend;
137
138            if (append && builder.length() < MAX_LENGTH) {
139                builder.append(replacement);
140                // remove all characters after the maximum length
141                if (builder.length() > MAX_LENGTH) {
142                    builder.delete(MAX_LENGTH, builder.length());
143                }
144                cachedString = null;
145            }
146
147            lastReplacement = replacement;
148        }
149
150        @Override
151        public String toString() {
152            if (cachedString == null) {
153                cachedString = builder.toString();
154            }
155            return cachedString;
156        }
157    }
158
159    /**
160     * Inner class for storing rules.
161     */
162    private static final class Rule {
163        private final String pattern;
164        private final String[] replacementAtStart;
165        private final String[] replacementBeforeVowel;
166        private final String[] replacementDefault;
167
168        protected Rule(final String pattern, final String replacementAtStart, final String replacementBeforeVowel,
169                final String replacementDefault) {
170            this.pattern = pattern;
171            this.replacementAtStart = replacementAtStart.split("\\|");
172            this.replacementBeforeVowel = replacementBeforeVowel.split("\\|");
173            this.replacementDefault = replacementDefault.split("\\|");
174        }
175
176        public int getPatternLength() {
177            return pattern.length();
178        }
179
180        public String[] getReplacements(final String context, final boolean atStart) {
181            if (atStart) {
182                return replacementAtStart;
183            }
184
185            final int nextIndex = getPatternLength();
186            final boolean nextCharIsVowel = nextIndex < context.length() ? isVowel(context.charAt(nextIndex)) : false;
187            if (nextCharIsVowel) {
188                return replacementBeforeVowel;
189            }
190
191            return replacementDefault;
192        }
193
194        private boolean isVowel(final char ch) {
195            return ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u';
196        }
197
198        public boolean matches(final String context) {
199            return context.startsWith(pattern);
200        }
201
202        @Override
203        public String toString() {
204            return String.format("%s=(%s,%s,%s)", pattern, Arrays.asList(replacementAtStart),
205                    Arrays.asList(replacementBeforeVowel), Arrays.asList(replacementDefault));
206        }
207    }
208
209    private static final String COMMENT = "//";
210    private static final String DOUBLE_QUOTE = "\"";
211
212    private static final String MULTILINE_COMMENT_END = "*/";
213
214    private static final String MULTILINE_COMMENT_START = "/*";
215
216    /** The resource file containing the replacement and folding rules */
217    private static final String RESOURCE_FILE = "org/apache/commons/codec/language/dmrules.txt";
218
219    /** The code length of a DM soundex value. */
220    private static final int MAX_LENGTH = 6;
221
222    /** Transformation rules indexed by the first character of their pattern. */
223    private static final Map<Character, List<Rule>> RULES = new HashMap<>();
224
225    /** Folding rules. */
226    private static final Map<Character, Character> FOLDINGS = new HashMap<>();
227
228    static {
229        final InputStream rulesIS = DaitchMokotoffSoundex.class.getClassLoader().getResourceAsStream(RESOURCE_FILE);
230        if (rulesIS == null) {
231            throw new IllegalArgumentException("Unable to load resource: " + RESOURCE_FILE);
232        }
233
234        try (final Scanner scanner = new Scanner(rulesIS, CharEncoding.UTF_8)) {
235            parseRules(scanner, RESOURCE_FILE, RULES, FOLDINGS);
236        }
237
238        // sort RULES by pattern length in descending order
239        for (final Map.Entry<Character, List<Rule>> rule : RULES.entrySet()) {
240            final List<Rule> ruleList = rule.getValue();
241            Collections.sort(ruleList, new Comparator<Rule>() {
242                @Override
243                public int compare(final Rule rule1, final Rule rule2) {
244                    return rule2.getPatternLength() - rule1.getPatternLength();
245                }
246            });
247        }
248    }
249
250    private static void parseRules(final Scanner scanner, final String location,
251            final Map<Character, List<Rule>> ruleMapping, final Map<Character, Character> asciiFoldings) {
252        int currentLine = 0;
253        boolean inMultilineComment = false;
254
255        while (scanner.hasNextLine()) {
256            currentLine++;
257            final String rawLine = scanner.nextLine();
258            String line = rawLine;
259
260            if (inMultilineComment) {
261                if (line.endsWith(MULTILINE_COMMENT_END)) {
262                    inMultilineComment = false;
263                }
264                continue;
265            }
266
267            if (line.startsWith(MULTILINE_COMMENT_START)) {
268                inMultilineComment = true;
269            } else {
270                // discard comments
271                final int cmtI = line.indexOf(COMMENT);
272                if (cmtI >= 0) {
273                    line = line.substring(0, cmtI);
274                }
275
276                // trim leading-trailing whitespace
277                line = line.trim();
278
279                if (line.length() == 0) {
280                    continue; // empty lines can be safely skipped
281                }
282
283                if (line.contains("=")) {
284                    // folding
285                    final String[] parts = line.split("=");
286                    if (parts.length != 2) {
287                        throw new IllegalArgumentException("Malformed folding statement split into " + parts.length +
288                                " parts: " + rawLine + " in " + location);
289                    }
290                    final String leftCharacter = parts[0];
291                    final String rightCharacter = parts[1];
292
293                    if (leftCharacter.length() != 1 || rightCharacter.length() != 1) {
294                        throw new IllegalArgumentException("Malformed folding statement - " +
295                                "patterns are not single characters: " + rawLine + " in " + location);
296                    }
297
298                    asciiFoldings.put(leftCharacter.charAt(0), rightCharacter.charAt(0));
299                } else {
300                    // rule
301                    final String[] parts = line.split("\\s+");
302                    if (parts.length != 4) {
303                        throw new IllegalArgumentException("Malformed rule statement split into " + parts.length +
304                                " parts: " + rawLine + " in " + location);
305                    }
306                    try {
307                        final String pattern = stripQuotes(parts[0]);
308                        final String replacement1 = stripQuotes(parts[1]);
309                        final String replacement2 = stripQuotes(parts[2]);
310                        final String replacement3 = stripQuotes(parts[3]);
311
312                        final Rule r = new Rule(pattern, replacement1, replacement2, replacement3);
313                        final char patternKey = r.pattern.charAt(0);
314                        List<Rule> rules = ruleMapping.get(patternKey);
315                        if (rules == null) {
316                            rules = new ArrayList<>();
317                            ruleMapping.put(patternKey, rules);
318                        }
319                        rules.add(r);
320                    } catch (final IllegalArgumentException e) {
321                        throw new IllegalStateException(
322                                "Problem parsing line '" + currentLine + "' in " + location, e);
323                    }
324                }
325            }
326        }
327    }
328
329    private static String stripQuotes(String str) {
330        if (str.startsWith(DOUBLE_QUOTE)) {
331            str = str.substring(1);
332        }
333
334        if (str.endsWith(DOUBLE_QUOTE)) {
335            str = str.substring(0, str.length() - 1);
336        }
337
338        return str;
339    }
340
341    /** Whether to use ASCII folding prior to encoding. */
342    private final boolean folding;
343
344    /**
345     * Creates a new instance with ASCII-folding enabled.
346     */
347    public DaitchMokotoffSoundex() {
348        this(true);
349    }
350
351    /**
352     * Creates a new instance.
353     * <p>
354     * With ASCII-folding enabled, certain accented characters will be transformed to equivalent ASCII characters, e.g.
355     * รจ -&gt; e.
356     * </p>
357     *
358     * @param folding
359     *            if ASCII-folding shall be performed before encoding
360     */
361    public DaitchMokotoffSoundex(final boolean folding) {
362        this.folding = folding;
363    }
364
365    /**
366     * Performs a cleanup of the input string before the actual soundex transformation.
367     * <p>
368     * Removes all whitespace characters and performs ASCII folding if enabled.
369     * </p>
370     *
371     * @param input
372     *            the input string to cleanup
373     * @return a cleaned up string
374     */
375    private String cleanup(final String input) {
376        final StringBuilder sb = new StringBuilder();
377        for (char ch : input.toCharArray()) {
378            if (Character.isWhitespace(ch)) {
379                continue;
380            }
381
382            ch = Character.toLowerCase(ch);
383            if (folding && FOLDINGS.containsKey(ch)) {
384                ch = FOLDINGS.get(ch);
385            }
386            sb.append(ch);
387        }
388        return sb.toString();
389    }
390
391    /**
392     * Encodes an Object using the Daitch-Mokotoff soundex algorithm without branching.
393     * <p>
394     * This method is provided in order to satisfy the requirements of the Encoder interface, and will throw an
395     * EncoderException if the supplied object is not of type java.lang.String.
396     * </p>
397     *
398     * @see #soundex(String)
399     *
400     * @param obj
401     *            Object to encode
402     * @return An object (of type java.lang.String) containing the DM soundex code, which corresponds to the String
403     *         supplied.
404     * @throws EncoderException
405     *             if the parameter supplied is not of type java.lang.String
406     * @throws IllegalArgumentException
407     *             if a character is not mapped
408     */
409    @Override
410    public Object encode(final Object obj) throws EncoderException {
411        if (!(obj instanceof String)) {
412            throw new EncoderException(
413                    "Parameter supplied to DaitchMokotoffSoundex encode is not of type java.lang.String");
414        }
415        return encode((String) obj);
416    }
417
418    /**
419     * Encodes a String using the Daitch-Mokotoff soundex algorithm without branching.
420     *
421     * @see #soundex(String)
422     *
423     * @param source
424     *            A String object to encode
425     * @return A DM Soundex code corresponding to the String supplied
426     * @throws IllegalArgumentException
427     *             if a character is not mapped
428     */
429    @Override
430    public String encode(final String source) {
431        if (source == null) {
432            return null;
433        }
434        return soundex(source, false)[0];
435    }
436
437    /**
438     * Encodes a String using the Daitch-Mokotoff soundex algorithm with branching.
439     * <p>
440     * In case a string is encoded into multiple codes (see branching rules), the result will contain all codes,
441     * separated by '|'.
442     * </p>
443     * <p>
444     * Example: the name "AUERBACH" is encoded as both
445     * </p>
446     * <ul>
447     * <li>097400</li>
448     * <li>097500</li>
449     * </ul>
450     * <p>
451     * Thus the result will be "097400|097500".
452     * </p>
453     *
454     * @param source
455     *            A String object to encode
456     * @return A string containing a set of DM Soundex codes corresponding to the String supplied
457     * @throws IllegalArgumentException
458     *             if a character is not mapped
459     */
460    public String soundex(final String source) {
461        final String[] branches = soundex(source, true);
462        final StringBuilder sb = new StringBuilder();
463        int index = 0;
464        for (final String branch : branches) {
465            sb.append(branch);
466            if (++index < branches.length) {
467                sb.append('|');
468            }
469        }
470        return sb.toString();
471    }
472
473    /**
474     * Perform the actual DM Soundex algorithm on the input string.
475     *
476     * @param source
477     *            A String object to encode
478     * @param branching
479     *            If branching shall be performed
480     * @return A string array containing all DM Soundex codes corresponding to the String supplied depending on the
481     *         selected branching mode
482     */
483    private String[] soundex(final String source, final boolean branching) {
484        if (source == null) {
485            return null;
486        }
487
488        final String input = cleanup(source);
489
490        final Set<Branch> currentBranches = new LinkedHashSet<>();
491        currentBranches.add(new Branch());
492
493        char lastChar = '\0';
494        for (int index = 0; index < input.length(); index++) {
495            final char ch = input.charAt(index);
496
497            // ignore whitespace inside a name
498            if (Character.isWhitespace(ch)) {
499                continue;
500            }
501
502            final String inputContext = input.substring(index);
503            final List<Rule> rules = RULES.get(ch);
504            if (rules == null) {
505                continue;
506            }
507
508            // use an EMPTY_LIST to avoid false positive warnings wrt potential null pointer access
509            @SuppressWarnings("unchecked")
510            final List<Branch> nextBranches = branching ? new ArrayList<Branch>() : Collections.EMPTY_LIST;
511
512            for (final Rule rule : rules) {
513                if (rule.matches(inputContext)) {
514                    if (branching) {
515                        nextBranches.clear();
516                    }
517                    final String[] replacements = rule.getReplacements(inputContext, lastChar == '\0');
518                    final boolean branchingRequired = replacements.length > 1 && branching;
519
520                    for (final Branch branch : currentBranches) {
521                        for (final String nextReplacement : replacements) {
522                            // if we have multiple replacements, always create a new branch
523                            final Branch nextBranch = branchingRequired ? branch.createBranch() : branch;
524
525                            // special rule: occurrences of mn or nm are treated differently
526                            final boolean force = (lastChar == 'm' && ch == 'n') || (lastChar == 'n' && ch == 'm');
527
528                            nextBranch.processNextReplacement(nextReplacement, force);
529
530                            if (branching) {
531                                nextBranches.add(nextBranch);
532                            } else {
533                                break;
534                            }
535                        }
536                    }
537
538                    if (branching) {
539                        currentBranches.clear();
540                        currentBranches.addAll(nextBranches);
541                    }
542                    index += rule.getPatternLength() - 1;
543                    break;
544                }
545            }
546
547            lastChar = ch;
548        }
549
550        final String[] result = new String[currentBranches.size()];
551        int index = 0;
552        for (final Branch branch : currentBranches) {
553            branch.finish();
554            result[index++] = branch.toString();
555        }
556
557        return result;
558    }
559}