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 *      https://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.text.similarity;
018
019import java.util.Locale;
020
021/**
022 * A matching algorithm that is similar to the searching algorithms implemented in editors such
023 * as Sublime Text, TextMate, Atom and others.
024 *
025 * <p>
026 * One point is given for every matched character. Subsequent matches yield two bonus points. A higher score
027 * indicates a higher similarity.
028 * </p>
029 *
030 * <p>
031 * This code has been adapted from Apache Commons Lang 3.3.
032 * </p>
033 *
034 * @since 1.0
035 */
036public class FuzzyScore {
037
038    /**
039     * Locale used to change the case of text.
040     */
041    private final Locale locale;
042
043    /**
044     * This returns a {@link Locale}-specific {@link FuzzyScore}.
045     *
046     * @param locale The string matching logic is case insensitive. A {@link Locale} is necessary to normalize both Strings to lower case.
047     * @throws IllegalArgumentException This is thrown if the {@link Locale} parameter is {@code null}.
048     */
049    public FuzzyScore(final Locale locale) {
050        if (locale == null) {
051            throw new IllegalArgumentException("Locale must not be null");
052        }
053        this.locale = locale;
054    }
055
056    /**
057     * Find the Fuzzy Score which indicates the similarity score between two Strings.
058     *
059     * <pre>
060     * score.fuzzyScore(null, null)                          = IllegalArgumentException
061     * score.fuzzyScore("not null", null)                    = IllegalArgumentException
062     * score.fuzzyScore(null, "not null")                    = IllegalArgumentException
063     * score.fuzzyScore("", "")                              = 0
064     * score.fuzzyScore("Workshop", "b")                     = 0
065     * score.fuzzyScore("Room", "o")                         = 1
066     * score.fuzzyScore("Workshop", "w")                     = 1
067     * score.fuzzyScore("Workshop", "ws")                    = 2
068     * score.fuzzyScore("Workshop", "wo")                    = 4
069     * score.fuzzyScore("Apache Software Foundation", "asf") = 3
070     * </pre>
071     *
072     * @param term  a full term that should be matched against, must not be null.
073     * @param query the query that will be matched against a term, must not be null.
074     * @return result score.
075     * @throws IllegalArgumentException if the term or query is {@code null}.
076     */
077    public Integer fuzzyScore(final CharSequence term, final CharSequence query) {
078        if (term == null || query == null) {
079            throw new IllegalArgumentException("CharSequences must not be null");
080        }
081
082        // fuzzy logic is case insensitive. We normalize the Strings to lower
083        // case right from the start. Turning characters to lower case
084        // via Character.toLowerCase(char) is unfortunately insufficient
085        // as it does not accept a locale.
086        final String termLowerCase = term.toString().toLowerCase(locale);
087        final String queryLowerCase = query.toString().toLowerCase(locale);
088
089        // the resulting score
090        int score = 0;
091
092        // the position in the term which will be scanned next for potential
093        // query character matches
094        int termIndex = 0;
095
096        // index of the previously matched character in the term
097        int previousMatchingCharacterIndex = Integer.MIN_VALUE;
098
099        for (int queryIndex = 0; queryIndex < queryLowerCase.length(); queryIndex++) {
100            final char queryChar = queryLowerCase.charAt(queryIndex);
101
102            boolean termCharacterMatchFound = false;
103            for (; termIndex < termLowerCase.length()
104                    && !termCharacterMatchFound; termIndex++) {
105                final char termChar = termLowerCase.charAt(termIndex);
106
107                if (queryChar == termChar) {
108                    // simple character matches result in one point
109                    score++;
110
111                    // subsequent character matches further improve
112                    // the score.
113                    if (previousMatchingCharacterIndex + 1 == termIndex) {
114                        score += 2;
115                    }
116
117                    previousMatchingCharacterIndex = termIndex;
118
119                    // we can leave the nested loop. Every character in the
120                    // query can match at most one character in the term.
121                    termCharacterMatchFound = true;
122                }
123            }
124        }
125
126        return score;
127    }
128
129    /**
130     * Gets the locale.
131     *
132     * @return The locale
133     */
134    public Locale getLocale() {
135        return locale;
136    }
137
138}