/*
 * 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.
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package org.apache.commons.codec.language.bm;

import java.io.InputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.EnumMap;
import java.util.HashSet;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Scanner;
import java.util.Set;
import java.util.regex.Pattern;

Language guessing utility.

This class encapsulates rules used to guess the possible languages that a word originates from. This is
done by reference to a whole series of rules distributed in resource files.

Instances of this class are typically managed through the static factory method instance().
Unless you are developing your own language guessing rules, you will not need to interact with this class directly.

This class is intended to be immutable and thread-safe.

Lang resources

Language guessing rules are typically loaded from resource files. These are UTF-8 encoded text files.
They are systematically named following the pattern:
org/apache/commons/codec/language/bm/lang.txt
The format of these resources is the following:

Rules: whitespace separated strings.
There should be 3 columns to each row, and these will be interpreted as:

pattern: a regular expression.
languages: a '+'-separated list of languages.
acceptOnMatch: 'true' or 'false' indicating if a match rules in or rules out the language.


End-of-line comments: Any occurrence of '//' will cause all text following on that line to be
discarded as a comment.
Multi-line comments: Any line starting with '/*' will start multi-line commenting mode.
This will skip all content until a line ending in '*' and '/' is found.
Blank lines: All blank lines will be skipped.


Port of lang.php
Since:
1.6
Version:
$Id$/**
 * Language guessing utility.
 * <p>
 * This class encapsulates rules used to guess the possible languages that a word originates from. This is
 * done by reference to a whole series of rules distributed in resource files.
 * <p>
 * Instances of this class are typically managed through the static factory method instance().
 * Unless you are developing your own language guessing rules, you will not need to interact with this class directly.
 * <p>
 * This class is intended to be immutable and thread-safe.
 * <p>
 * <b>Lang resources</b>
 * <p>
 * Language guessing rules are typically loaded from resource files. These are UTF-8 encoded text files.
 * They are systematically named following the pattern:
 * <blockquote>org/apache/commons/codec/language/bm/lang.txt</blockquote>
 * The format of these resources is the following:
 * <ul>
 * <li><b>Rules:</b> whitespace separated strings.
 * There should be 3 columns to each row, and these will be interpreted as:
 * <ol>
 * <li>pattern: a regular expression.</li>
 * <li>languages: a '+'-separated list of languages.</li>
 * <li>acceptOnMatch: 'true' or 'false' indicating if a match rules in or rules out the language.</li>
 * </ol>
 * </li>
 * <li><b>End-of-line comments:</b> Any occurrence of '//' will cause all text following on that line to be
 * discarded as a comment.</li>
 * <li><b>Multi-line comments:</b> Any line starting with '/*' will start multi-line commenting mode.
 * This will skip all content until a line ending in '*' and '/' is found.</li>
 * <li><b>Blank lines:</b> All blank lines will be skipped.</li>
 * </ul>
 * <p>
 * Port of lang.php
 *
 * @since 1.6
 * @version $Id$
 */
public class Lang {
    // Implementation note: This class is divided into two sections. The first part is a static factory interface that
    // exposes the LANGUAGE_RULES_RN resource as a Lang instance. The second part is the Lang instance methods that
    // encapsulate a particular language-guessing rule table and the language guessing itself.
    //
    // It may make sense in the future to expose the private constructor to allow power users to build custom language-
    // guessing rules, perhaps by marking it protected and allowing sub-classing. However, the vast majority of users
    // should be strongly encouraged to use the static factory <code>instance</code> method to get their Lang instances.

    private static final class LangRule {
        private final boolean acceptOnMatch;
        private final Set<String> languages;
        private final Pattern pattern;

        private LangRule(final Pattern pattern, final Set<String> languages, final boolean acceptOnMatch) {
            this.pattern = pattern;
            this.languages = languages;
            this.acceptOnMatch = acceptOnMatch;
        }

        public boolean matches(final String txt) {
            return this.pattern.matcher(txt).find();
        }
    }

    private static final Map<NameType, Lang> Langs = new EnumMap<>(NameType.class);

    private static final String LANGUAGE_RULES_RN = "org/apache/commons/codec/language/bm/%s_lang.txt";

    static {
        for (final NameType s : NameType.values()) {
            Langs.put(s, loadFromResource(String.format(LANGUAGE_RULES_RN, s.getName()), Languages.getInstance(s)));
        }
    }

    
Gets a Lang instance for one of the supported NameTypes.
Params:
nameType – 
           the NameType to look up
Returns:
a Lang encapsulating the language guessing rules for that name type/**
     * Gets a Lang instance for one of the supported NameTypes.
     *
     * @param nameType
     *            the NameType to look up
     * @return a Lang encapsulating the language guessing rules for that name type
     */
    public static Lang instance(final NameType nameType) {
        return Langs.get(nameType);
    }

    
Loads language rules from a resource.
 In normal use, you will obtain instances of Lang through the instance(NameType) method. You will only need to call this yourself if you are developing custom language mapping rules. 
Params:
languageRulesResourceName – 
           the fully-qualified resource name to load
languages – 
           the languages that these rules will support
Returns:
a Lang encapsulating the loaded language-guessing rules./**
     * Loads language rules from a resource.
     * <p>
     * In normal use, you will obtain instances of Lang through the {@link #instance(NameType)} method.
     * You will only need to call this yourself if you are developing custom language mapping rules.
     *
     * @param languageRulesResourceName
     *            the fully-qualified resource name to load
     * @param languages
     *            the languages that these rules will support
     * @return a Lang encapsulating the loaded language-guessing rules.
     */
    public static Lang loadFromResource(final String languageRulesResourceName, final Languages languages) {
        final List<LangRule> rules = new ArrayList<>();
        final InputStream lRulesIS = Lang.class.getClassLoader().getResourceAsStream(languageRulesResourceName);

        if (lRulesIS == null) {
            throw new IllegalStateException("Unable to resolve required resource:" + LANGUAGE_RULES_RN);
        }

        try (final Scanner scanner = new Scanner(lRulesIS, ResourceConstants.ENCODING)) {
            boolean inExtendedComment = false;
            while (scanner.hasNextLine()) {
                final String rawLine = scanner.nextLine();
                String line = rawLine;
                if (inExtendedComment) {
                    // check for closing comment marker, otherwise discard doc comment line
                    if (line.endsWith(ResourceConstants.EXT_CMT_END)) {
                        inExtendedComment = false;
                    }
                } else {
                    if (line.startsWith(ResourceConstants.EXT_CMT_START)) {
                        inExtendedComment = true;
                    } else {
                        // discard comments
                        final int cmtI = line.indexOf(ResourceConstants.CMT);
                        if (cmtI >= 0) {
                            line = line.substring(0, cmtI);
                        }

                        // trim leading-trailing whitespace
                        line = line.trim();

                        if (line.length() == 0) {
                            continue; // empty lines can be safely skipped
                        }

                        // split it up
                        final String[] parts = line.split("\\s+");

                        if (parts.length != 3) {
                            throw new IllegalArgumentException("Malformed line '" + rawLine +
                                    "' in language resource '" + languageRulesResourceName + "'");
                        }

                        final Pattern pattern = Pattern.compile(parts[0]);
                        final String[] langs = parts[1].split("\\+");
                        final boolean accept = parts[2].equals("true");

                        rules.add(new LangRule(pattern, new HashSet<>(Arrays.asList(langs)), accept));
                    }
                }
            }
        }
        return new Lang(rules, languages);
    }

    private final Languages languages;
    private final List<LangRule> rules;

    private Lang(final List<LangRule> rules, final Languages languages) {
        this.rules = Collections.unmodifiableList(rules);
        this.languages = languages;
    }

    
Guesses the language of a word.
Params:
text – 
           the word
Returns:
the language that the word originates from or Languages.ANY if there was no unique match/**
     * Guesses the language of a word.
     *
     * @param text
     *            the word
     * @return the language that the word originates from or {@link Languages#ANY} if there was no unique match
     */
    public String guessLanguage(final String text) {
        final Languages.LanguageSet ls = guessLanguages(text);
        return ls.isSingleton() ? ls.getAny() : Languages.ANY;
    }

    
Guesses the languages of a word.
Params:
input – 
           the word
Returns:
a Set of Strings of language names that are potential matches for the input word/**
     * Guesses the languages of a word.
     *
     * @param input
     *            the word
     * @return a Set of Strings of language names that are potential matches for the input word
     */
    public Languages.LanguageSet guessLanguages(final String input) {
        final String text = input.toLowerCase(Locale.ENGLISH);

        final Set<String> langs = new HashSet<>(this.languages.getLanguages());
        for (final LangRule rule : this.rules) {
            if (rule.matches(text)) {
                if (rule.acceptOnMatch) {
                    langs.retainAll(rule.languages);
                } else {
                    langs.removeAll(rule.languages);
                }
            }
        }

        final Languages.LanguageSet ls = Languages.LanguageSet.from(langs);
        return ls.equals(Languages.NO_LANGUAGES) ? Languages.ANY_LANGUAGE : ls;
    }
}