/*
 * 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.
 */
package org.apache.commons.lang3;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Locale;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

Operations to assist when working with a Locale.
This class tries to handle null input gracefully. An exception will not be thrown for a null input. Each method documents its behaviour in more detail.
Since:
2.2/**
 * <p>Operations to assist when working with a {@link Locale}.</p>
 *
 * <p>This class tries to handle {@code null} input gracefully.
 * An exception will not be thrown for a {@code null} input.
 * Each method documents its behaviour in more detail.</p>
 *
 * @since 2.2
 */
public class LocaleUtils {

    
Concurrent map of language locales by country. /** Concurrent map of language locales by country. */
    private static final ConcurrentMap<String, List<Locale>> cLanguagesByCountry =
        new ConcurrentHashMap<>();

    
Concurrent map of country locales by language. /** Concurrent map of country locales by language. */
    private static final ConcurrentMap<String, List<Locale>> cCountriesByLanguage =
        new ConcurrentHashMap<>();

    
LocaleUtils instances should NOT be constructed in standard programming. Instead, the class should be used as LocaleUtils.toLocale("en_GB");.
This constructor is public to permit tools that require a JavaBean instance
to operate.
/**
     * <p>{@code LocaleUtils} instances should NOT be constructed in standard programming.
     * Instead, the class should be used as {@code LocaleUtils.toLocale("en_GB");}.</p>
     *
     * <p>This constructor is public to permit tools that require a JavaBean instance
     * to operate.</p>
     */
    public LocaleUtils() {
      super();
    }

    //-----------------------------------------------------------------------
    
Converts a String to a Locale.
This method takes the string format of a locale and creates the
locale object from it.
  LocaleUtils.toLocale("")           = new Locale("", "")
  LocaleUtils.toLocale("en")         = new Locale("en", "")
  LocaleUtils.toLocale("en_GB")      = new Locale("en", "GB")
  LocaleUtils.toLocale("en_001")     = new Locale("en", "001")
  LocaleUtils.toLocale("en_GB_xxx")  = new Locale("en", "GB", "xxx")   (#)

(#) The behaviour of the JDK variant constructor changed between JDK1.3 and JDK1.4.
In JDK1.3, the constructor upper cases the variant, in JDK1.4, it doesn't.
Thus, the result from getVariant() may vary depending on your JDK.
This method validates the input strictly.
The language code must be lowercase.
The country code must be uppercase.
The separator must be an underscore.
The length must be correct.

Params:
str –  the locale String to convert, null returns null
Throws:
IllegalArgumentException – if the string is an invalid format
See Also:
Locale.forLanguageTag(String)
Returns:
a Locale, null if null input/**
     * <p>Converts a String to a Locale.</p>
     *
     * <p>This method takes the string format of a locale and creates the
     * locale object from it.</p>
     *
     * <pre>
     *   LocaleUtils.toLocale("")           = new Locale("", "")
     *   LocaleUtils.toLocale("en")         = new Locale("en", "")
     *   LocaleUtils.toLocale("en_GB")      = new Locale("en", "GB")
     *   LocaleUtils.toLocale("en_001")     = new Locale("en", "001")
     *   LocaleUtils.toLocale("en_GB_xxx")  = new Locale("en", "GB", "xxx")   (#)
     * </pre>
     *
     * <p>(#) The behaviour of the JDK variant constructor changed between JDK1.3 and JDK1.4.
     * In JDK1.3, the constructor upper cases the variant, in JDK1.4, it doesn't.
     * Thus, the result from getVariant() may vary depending on your JDK.</p>
     *
     * <p>This method validates the input strictly.
     * The language code must be lowercase.
     * The country code must be uppercase.
     * The separator must be an underscore.
     * The length must be correct.
     * </p>
     *
     * @param str  the locale String to convert, null returns null
     * @return a Locale, null if null input
     * @throws IllegalArgumentException if the string is an invalid format
     * @see Locale#forLanguageTag(String)
     */
    public static Locale toLocale(final String str) {
        if (str == null) {
            return null;
        }
        if (str.isEmpty()) { // LANG-941 - JDK 8 introduced an empty locale where all fields are blank
            return new Locale(StringUtils.EMPTY, StringUtils.EMPTY);
        }
        if (str.contains("#")) { // LANG-879 - Cannot handle Java 7 script & extensions
            throw new IllegalArgumentException("Invalid locale format: " + str);
        }
        final int len = str.length();
        if (len < 2) {
            throw new IllegalArgumentException("Invalid locale format: " + str);
        }
        final char ch0 = str.charAt(0);
        if (ch0 == '_') {
            if (len < 3) {
                throw new IllegalArgumentException("Invalid locale format: " + str);
            }
            final char ch1 = str.charAt(1);
            final char ch2 = str.charAt(2);
            if (!Character.isUpperCase(ch1) || !Character.isUpperCase(ch2)) {
                throw new IllegalArgumentException("Invalid locale format: " + str);
            }
            if (len == 3) {
                return new Locale(StringUtils.EMPTY, str.substring(1, 3));
            }
            if (len < 5) {
                throw new IllegalArgumentException("Invalid locale format: " + str);
            }
            if (str.charAt(3) != '_') {
                throw new IllegalArgumentException("Invalid locale format: " + str);
            }
            return new Locale(StringUtils.EMPTY, str.substring(1, 3), str.substring(4));
        }

        return parseLocale(str);
    }

    
Tries to parse a locale from the given String.
Params:
str – the String to parse a locale from.
Throws:
IllegalArgumentException – if the given String can not be parsed.
Returns:
a Locale instance parsed from the given String./**
     * Tries to parse a locale from the given String.
     *
     * @param str the String to parse a locale from.
     * @return a Locale instance parsed from the given String.
     * @throws IllegalArgumentException if the given String can not be parsed.
     */
    private static Locale parseLocale(final String str) {
        if (isISO639LanguageCode(str)) {
            return new Locale(str);
        }

        final String[] segments = str.split("_", -1);
        final String language = segments[0];
        if (segments.length == 2) {
            final String country = segments[1];
            if (isISO639LanguageCode(language) && isISO3166CountryCode(country) ||
                    isNumericAreaCode(country)) {
                return new Locale(language, country);
            }
        } else if (segments.length == 3) {
            final String country = segments[1];
            final String variant = segments[2];
            if (isISO639LanguageCode(language) &&
                    (country.length() == 0 || isISO3166CountryCode(country) || isNumericAreaCode(country)) &&
                    variant.length() > 0) {
                return new Locale(language, country, variant);
            }
        }
        throw new IllegalArgumentException("Invalid locale format: " + str);
    }

    
Checks whether the given String is a ISO 639 compliant language code.
Params:
str – the String to check.
Returns:
true, if the given String is a ISO 639 compliant language code./**
     * Checks whether the given String is a ISO 639 compliant language code.
     *
     * @param str the String to check.
     * @return true, if the given String is a ISO 639 compliant language code.
     */
    private static boolean isISO639LanguageCode(final String str) {
        return StringUtils.isAllLowerCase(str) && (str.length() == 2 || str.length() == 3);
    }

    
Checks whether the given String is a ISO 3166 alpha-2 country code.
Params:
str – the String to check
Returns:
true, is the given String is a ISO 3166 compliant country code./**
     * Checks whether the given String is a ISO 3166 alpha-2 country code.
     *
     * @param str the String to check
     * @return true, is the given String is a ISO 3166 compliant country code.
     */
    private static boolean isISO3166CountryCode(final String str) {
        return StringUtils.isAllUpperCase(str) && str.length() == 2;
    }

    
Checks whether the given String is a UN M.49 numeric area code.
Params:
str – the String to check
Returns:
true, is the given String is a UN M.49 numeric area code./**
     * Checks whether the given String is a UN M.49 numeric area code.
     *
     * @param str the String to check
     * @return true, is the given String is a UN M.49 numeric area code.
     */
    private static boolean isNumericAreaCode(final String str) {
        return StringUtils.isNumeric(str) && str.length() == 3;
    }

    //-----------------------------------------------------------------------
    
Obtains the list of locales to search through when performing
a locale search.
localeLookupList(Locale("fr","CA","xxx"))
  = [Locale("fr","CA","xxx"), Locale("fr","CA"), Locale("fr")]

Params:
locale –  the locale to start from
Returns:
the unmodifiable list of Locale objects, 0 being locale, not null/**
     * <p>Obtains the list of locales to search through when performing
     * a locale search.</p>
     *
     * <pre>
     * localeLookupList(Locale("fr","CA","xxx"))
     *   = [Locale("fr","CA","xxx"), Locale("fr","CA"), Locale("fr")]
     * </pre>
     *
     * @param locale  the locale to start from
     * @return the unmodifiable list of Locale objects, 0 being locale, not null
     */
    public static List<Locale> localeLookupList(final Locale locale) {
        return localeLookupList(locale, locale);
    }

    //-----------------------------------------------------------------------
    
Obtains the list of locales to search through when performing
a locale search.
localeLookupList(Locale("fr", "CA", "xxx"), Locale("en"))
  = [Locale("fr","CA","xxx"), Locale("fr","CA"), Locale("fr"), Locale("en"]

The result list begins with the most specific locale, then the
next more general and so on, finishing with the default locale.
The list will never contain the same locale twice.
Params:
locale –  the locale to start from, null returns empty list
defaultLocale –  the default locale to use if no other is found
Returns:
the unmodifiable list of Locale objects, 0 being locale, not null/**
     * <p>Obtains the list of locales to search through when performing
     * a locale search.</p>
     *
     * <pre>
     * localeLookupList(Locale("fr", "CA", "xxx"), Locale("en"))
     *   = [Locale("fr","CA","xxx"), Locale("fr","CA"), Locale("fr"), Locale("en"]
     * </pre>
     *
     * <p>The result list begins with the most specific locale, then the
     * next more general and so on, finishing with the default locale.
     * The list will never contain the same locale twice.</p>
     *
     * @param locale  the locale to start from, null returns empty list
     * @param defaultLocale  the default locale to use if no other is found
     * @return the unmodifiable list of Locale objects, 0 being locale, not null
     */
    public static List<Locale> localeLookupList(final Locale locale, final Locale defaultLocale) {
        final List<Locale> list = new ArrayList<>(4);
        if (locale != null) {
            list.add(locale);
            if (locale.getVariant().length() > 0) {
                list.add(new Locale(locale.getLanguage(), locale.getCountry()));
            }
            if (locale.getCountry().length() > 0) {
                list.add(new Locale(locale.getLanguage(), StringUtils.EMPTY));
            }
            if (!list.contains(defaultLocale)) {
                list.add(defaultLocale);
            }
        }
        return Collections.unmodifiableList(list);
    }

    //-----------------------------------------------------------------------
    
Obtains an unmodifiable list of installed locales.
This method is a wrapper around Locale.getAvailableLocales(). It is more efficient, as the JDK method must create a new array each time it is called.
Returns:
the unmodifiable list of available locales/**
     * <p>Obtains an unmodifiable list of installed locales.</p>
     *
     * <p>This method is a wrapper around {@link Locale#getAvailableLocales()}.
     * It is more efficient, as the JDK method must create a new array each
     * time it is called.</p>
     *
     * @return the unmodifiable list of available locales
     */
    public static List<Locale> availableLocaleList() {
        return SyncAvoid.AVAILABLE_LOCALE_LIST;
    }

    //-----------------------------------------------------------------------
    
Obtains an unmodifiable set of installed locales.
This method is a wrapper around Locale.getAvailableLocales(). It is more efficient, as the JDK method must create a new array each time it is called.
Returns:
the unmodifiable set of available locales/**
     * <p>Obtains an unmodifiable set of installed locales.</p>
     *
     * <p>This method is a wrapper around {@link Locale#getAvailableLocales()}.
     * It is more efficient, as the JDK method must create a new array each
     * time it is called.</p>
     *
     * @return the unmodifiable set of available locales
     */
    public static Set<Locale> availableLocaleSet() {
        return SyncAvoid.AVAILABLE_LOCALE_SET;
    }

    //-----------------------------------------------------------------------
    
Checks if the locale specified is in the list of available locales.
Params:
locale – the Locale object to check if it is available
Returns:
true if the locale is a known locale/**
     * <p>Checks if the locale specified is in the list of available locales.</p>
     *
     * @param locale the Locale object to check if it is available
     * @return true if the locale is a known locale
     */
    public static boolean isAvailableLocale(final Locale locale) {
        return availableLocaleList().contains(locale);
    }

    //-----------------------------------------------------------------------
    
Obtains the list of languages supported for a given country.
This method takes a country code and searches to find the
languages available for that country. Variant locales are removed.
Params:
countryCode –  the 2 letter country code, null returns empty
Returns:
an unmodifiable List of Locale objects, not null/**
     * <p>Obtains the list of languages supported for a given country.</p>
     *
     * <p>This method takes a country code and searches to find the
     * languages available for that country. Variant locales are removed.</p>
     *
     * @param countryCode  the 2 letter country code, null returns empty
     * @return an unmodifiable List of Locale objects, not null
     */
    public static List<Locale> languagesByCountry(final String countryCode) {
        if (countryCode == null) {
            return Collections.emptyList();
        }
        List<Locale> langs = cLanguagesByCountry.get(countryCode);
        if (langs == null) {
            langs = new ArrayList<>();
            final List<Locale> locales = availableLocaleList();
            for (final Locale locale : locales) {
                if (countryCode.equals(locale.getCountry()) &&
                    locale.getVariant().isEmpty()) {
                    langs.add(locale);
                }
            }
            langs = Collections.unmodifiableList(langs);
            cLanguagesByCountry.putIfAbsent(countryCode, langs);
            langs = cLanguagesByCountry.get(countryCode);
        }
        return langs;
    }

    //-----------------------------------------------------------------------
    
Obtains the list of countries supported for a given language.
This method takes a language code and searches to find the
countries available for that language. Variant locales are removed.
Params:
languageCode –  the 2 letter language code, null returns empty
Returns:
an unmodifiable List of Locale objects, not null/**
     * <p>Obtains the list of countries supported for a given language.</p>
     *
     * <p>This method takes a language code and searches to find the
     * countries available for that language. Variant locales are removed.</p>
     *
     * @param languageCode  the 2 letter language code, null returns empty
     * @return an unmodifiable List of Locale objects, not null
     */
    public static List<Locale> countriesByLanguage(final String languageCode) {
        if (languageCode == null) {
            return Collections.emptyList();
        }
        List<Locale> countries = cCountriesByLanguage.get(languageCode);
        if (countries == null) {
            countries = new ArrayList<>();
            final List<Locale> locales = availableLocaleList();
            for (final Locale locale : locales) {
                if (languageCode.equals(locale.getLanguage()) &&
                    locale.getCountry().length() != 0 &&
                    locale.getVariant().isEmpty()) {
                    countries.add(locale);
                }
            }
            countries = Collections.unmodifiableList(countries);
            cCountriesByLanguage.putIfAbsent(languageCode, countries);
            countries = cCountriesByLanguage.get(languageCode);
        }
        return countries;
    }

    //-----------------------------------------------------------------------
    // class to avoid synchronization (Init on demand)
    static class SyncAvoid {
        
Unmodifiable list of available locales. /** Unmodifiable list of available locales. */
        private static final List<Locale> AVAILABLE_LOCALE_LIST;
        
Unmodifiable set of available locales. /** Unmodifiable set of available locales. */
        private static final Set<Locale> AVAILABLE_LOCALE_SET;

        static {
            final List<Locale> list = new ArrayList<>(Arrays.asList(Locale.getAvailableLocales()));  // extra safe
            AVAILABLE_LOCALE_LIST = Collections.unmodifiableList(list);
            AVAILABLE_LOCALE_SET = Collections.unmodifiableSet(new HashSet<>(list));
        }
    }

}