/*
    * 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
    *
    *      https://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.Comparator;
  import java.util.LinkedHashSet;
  import java.util.List;
  import java.util.Locale;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  import java.util.function.Predicate;
  import java.util.stream.Collectors;
  
  /**
   * Operations to assist when working with a {@link Locale}.
   *
   * <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 behavior in
   * more detail.
   * </p>
   *
   * @see Locale
   * @since 2.2
   */
  public class LocaleUtils {
  
      /**
       * Avoids synchronization, initializes on demand.
       */
      private static final class SyncAvoid {
  
          /** Private unmodifiable and sorted list of available locales. */
          private static final List<Locale> AVAILABLE_LOCALE_ULIST;
  
          /** Private unmodifiable set of available locales. */
          private static final Set<Locale> AVAILABLE_LOCALE_USET;
          static {
              AVAILABLE_LOCALE_ULIST = Collections
                      .unmodifiableList(Arrays.asList(ArraySorter.sort(Locale.getAvailableLocales(), Comparator.comparing(Locale::toString))));
              AVAILABLE_LOCALE_USET = Collections.unmodifiableSet(new LinkedHashSet<>(AVAILABLE_LOCALE_ULIST));
          }
      }
  
      /**
       * The underscore character {@code '}{@value}{@code '}.
       */
      private static final char UNDERSCORE = '_';
  
      /**
       * The undetermined language {@value}.
       * <p>
       * If a language is empty, or not <em>well-formed</em> (for example "a" or "e2"), {@link Locale#toLanguageTag()} will return {@code "und"} (Undetermined).
       * </p>
       *
       * @see Locale#toLanguageTag()
       */
      private static final String UNDETERMINED = "und";
  
      /**
       * The dash character {@code '}{@value}{@code '}.
       */
      private static final char DASH = '-';
  
      /**
       * Concurrent map of language locales by country.
       */
      private static final ConcurrentMap<String, List<Locale>> ccToLocalesMap = new ConcurrentHashMap<>();
  
  
      /**
       * Concurrent map of country locales by language.
       */
      private static final ConcurrentMap<String, List<Locale>> lcToLocalesMap = new ConcurrentHashMap<>();
  
      /**
       * Gets an unmodifiable and sorted list of installed locales.
       *
       * <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 and sorted list of available locales.
      */
     public static List<Locale> availableLocaleList() {
         return SyncAvoid.AVAILABLE_LOCALE_ULIST;
     }
 
     private static List<Locale> availableLocaleList(final Predicate<Locale> predicate) {
         return availableLocaleList().stream().filter(predicate).collect(Collectors.toList());
     }
 
     /**
      * Gets an unmodifiable set of installed locales.
      *
      * <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_USET;
     }
 
     /**
      * Gets the list of countries supported for a given language.
      *
      * <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) {
         // Only syntactically valid ISO 639 codes can match an available locale's language; anything
         // else is answered without touching the cache so that arbitrary caller strings are never
         // retained for the lifetime of the class loader.
         if (languageCode == null || !languageCode.isEmpty() && !isISO639LanguageCode(languageCode)) {
             return Collections.emptyList();
         }
         return lcToLocalesMap.computeIfAbsent(languageCode, lc -> Collections
                 .unmodifiableList(availableLocaleList(locale -> languageCode.equals(locale.getLanguage()) && !hasCountry(locale) && hasVariant(locale))));
     }
 
     static ConcurrentMap<String, List<Locale>> getCcToLocalesMap() {
         return ccToLocalesMap;
     }
 
     /**
      * Gets the cache of country locales by language.
      *
      * @return the cache of country locales by language.
      */
     static ConcurrentMap<String, List<Locale>> getLcToLocalesMap() {
         return lcToLocalesMap;
     }
 
     /**
      * Tests whether the given Locale defines a variant.
      *
      * @param locale The Locale to test.
      * @return whether the given Locale defines a variant.
      */
     private static boolean hasCountry(final Locale locale) {
         return locale.getCountry().isEmpty();
     }
 
     /**
      * Tests whether the given Locale defines a country.
      *
      * @param locale The Locale to test.
      * @return whether the given Locale defines a country.
      */
     private static boolean hasVariant(final Locale locale) {
         return locale.getVariant().isEmpty();
     }
 
     /**
      * Tests whether the given string is the length of an <a href="https://www.iso.org/iso-3166-country-codes.html">ISO 3166</a> alpha-2 country code.
      *
      * @param str The string to test.
      * @return whether the given string is the length of an <a href="https://www.iso.org/iso-3166-country-codes.html">ISO 3166</a> alpha-2 country code.
      */
     private static boolean isAlpha2Len(final String str) {
         return str.length() == 2;
     }
 
     /**
      * Tests whether the given string is the length of an <a href="https://www.iso.org/iso-3166-country-codes.html">ISO 3166</a> alpha-3 country code.
      *
      * @param str The string to test.
      * @return whether the given string is the length of an <a href="https://www.iso.org/iso-3166-country-codes.html">ISO 3166</a> alpha-3 country code.
      */
     private static boolean isAlpha3Len(final String str) {
         return str.length() == 3;
     }
 
     /**
      * Tests whether the locale specified is in the set of available locales.
      *
      * @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 availableLocaleSet().contains(locale);
     }
 
     /**
      * Tests whether the given String is a <a href="https://www.iso.org/iso-3166-country-codes.html">ISO 3166</a> alpha-2 country code.
      *
      * @param str The String to check.
      * @return true if the given String is a <a href="https://www.iso.org/iso-3166-country-codes.html">ISO 3166</a> compliant country code.
      */
     private static boolean isISO3166CountryCode(final String str) {
         return StringUtils.isAllUpperCase(str) && isAlpha2Len(str);
     }
 
     /**
      * Tests whether the given String is a <a href="https://www.iso.org/iso-639-language-code">ISO 639</a> compliant language code.
      *
      * @param str The String to check.
      * @return true, if the given String is a <a href="https://www.iso.org/iso-639-language-code">ISO 639</a> compliant language code.
      */
     private static boolean isISO639LanguageCode(final String str) {
         return StringUtils.isAllLowerCase(str) && (isAlpha2Len(str) || isAlpha3Len(str));
     }
 
     /**
      * Tests whether a Locale's language is undetermined.
      * <p>
      * A Locale's language tag is undetermined if it's value is {@code "und"}. If a language is empty, or not well-formed (for example, "a" or "e2"), it will be
      * equal to {@code "und"}.
      * </p>
      *
      * @param locale The locale to test.
      * @return whether a Locale's language is undetermined.
      * @see Locale#toLanguageTag()
      * @since 3.14.0
      */
     public static boolean isLanguageUndetermined(final Locale locale) {
         return locale == null || UNDETERMINED.equals(locale.toLanguageTag());
     }
 
     /**
      * Tests whether the given String is a UN M.49 numeric area code.
      *
      * @param str The String to check.
      * @return true if the given String is a UN M.49 numeric area code.
      */
     private static boolean isNumericAreaCode(final String str) {
         return StringUtils.isNumeric(str) && isAlpha3Len(str);
     }
 
     /**
      * Obtains the list of languages supported for a given country.
      *
      * <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) {
         // Only syntactically valid ISO 3166 alpha-2 / UN M.49 numeric codes can match an available
         // locale's country; anything else is answered without touching the cache so that arbitrary
         // caller strings are never retained for the lifetime of the class loader.
         if (countryCode == null || !countryCode.isEmpty() && !isISO3166CountryCode(countryCode) && !isNumericAreaCode(countryCode)) {
             return Collections.emptyList();
         }
         return ccToLocalesMap.computeIfAbsent(countryCode,
                 k -> Collections.unmodifiableList(availableLocaleList(locale -> countryCode.equals(locale.getCountry()) && hasVariant(locale))));
     }
 
     /**
      * Obtains the list of locales to search through when performing a locale search.
      *
      * <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.
      *
      * <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 (!hasVariant(locale)) {
                 list.add(new Locale(locale.getLanguage(), locale.getCountry()));
             }
             if (!hasCountry(locale)) {
                 list.add(new Locale(locale.getLanguage(), StringUtils.EMPTY));
             }
             if (!list.contains(defaultLocale)) {
                 list.add(defaultLocale);
             }
         }
         return Collections.unmodifiableList(list);
     }
 
     /**
      * Creates new {@linkplain Locale} for the given country.
      *
      * @param country An ISO 3166 alpha-2 country code or a UN M.49 numeric-3 area code. See the {@linkplain Locale} class description about valid country
      *                values.
      * @throws NullPointerException Thrown if either argument is null.
      * @return A new Locale for the given country.
      * @see Locale#Locale(String, String)
      */
     static Locale ofCountry(final String country) {
         return new Locale(StringUtils.EMPTY, country);
     }
 
     /**
      * Tries to parse a Locale from the given String.
      * <p>
      * See {@link Locale} for the format.
      * </p>
      *
      * @param str The String to parse as a Locale.
      * @return A Locale parsed from the given String.
      * @throws IllegalArgumentException Thrown if the given String cannot be parsed.
      * @see Locale
      * @see <a href="https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/Locale.html#special_cases_constructor">Locale special cases</a>
      */
     private static Locale parseLocale(final String str) {
         if (isISO639LanguageCode(str)) {
             return new Locale(str);
         }
         final int limit = 3;
         final char separator = str.indexOf(UNDERSCORE) != -1 ? UNDERSCORE : DASH;
         final String[] segments = str.split(String.valueOf(separator), 3);
         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 == limit) {
             final String country = segments[1];
             final String variant = segments[2];
             // Special case 1: https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/Locale.html#special_cases_constructor
             if (str.equals("th_TH_TH_#u-nu-thai")) {
                 return new Locale(language, country, "TH");
             }
             // Special case 2: https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/Locale.html#special_cases_constructor
             if (str.equals("ja_JP_JP_#u-ca-japanese")) {
                 return new Locale(language, country, "JP");
             }
             if (isISO639LanguageCode(language) && (country.isEmpty() || isISO3166CountryCode(country) || isNumericAreaCode(country)) && !variant.isEmpty()) {
                 return new Locale(language, country, variant);
             }
         }
         if (ArrayUtils.contains(Locale.getISOCountries(), str)) {
             return new Locale(StringUtils.EMPTY, str);
         }
         throw new IllegalArgumentException("Invalid locale format: " + str);
     }
 
     /**
      * Returns the given locale if non-{@code null}, otherwise {@link Locale#getDefault()}.
      *
      * @param locale A locale or {@code null}.
      * @return The given locale if non-{@code null}, otherwise {@link Locale#getDefault()}.
      * @since 3.12.0
      */
     public static Locale toLocale(final Locale locale) {
         return locale != null ? locale : Locale.getDefault();
     }
 
     /**
      * Converts a String to a Locale.
      *
      * <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-GB")      = new Locale("en", "GB")
      *   LocaleUtils.toLocale("en_001")     = new Locale("en", "001")
      *   LocaleUtils.toLocale("en_GB_xxx")  = new Locale("en", "GB", "xxx")   (#)
      *   LocaleUtils.toLocale("US")         = new Locale("", "US") // Because "US" is Locale.getISOCountries()
      * </pre>
      *
      * <p>
      * (#) The behavior 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 or
      * a dash. 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 Thrown if the string is an invalid format.
      * @see Locale#forLanguageTag(String)
      * @see Locale#getISOCountries()
      * @see <a href="https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/Locale.html#special_cases_constructor">Locale special cases</a>
      */
     public static Locale toLocale(final String str) {
         if (str == null) {
             // TODO Should this return the default locale?
             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);
         }
         final int len = str.length();
         if (len < 2) {
             throw new IllegalArgumentException("Invalid locale format: " + str);
         }
         final char ch0 = str.charAt(0);
         if (ch0 == UNDERSCORE || ch0 == DASH) {
             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 || str.charAt(3) != ch0) {
                 throw new IllegalArgumentException("Invalid locale format: " + str);
             }
             return new Locale(StringUtils.EMPTY, str.substring(1, 3), str.substring(4));
         }
         return parseLocale(str);
     }
 
     /**
      * {@link LocaleUtils} instances should NOT be constructed in standard programming. Instead, the class should be used as
      * {@code LocaleUtils.toLocale("en_GB");}.
      *
      * <p>
      * This constructor is public to permit tools that require a JavaBean instance to operate.
      * </p>
      *
      * @deprecated TODO Make private in 4.0.
      */
     @Deprecated
     public LocaleUtils() {
         // empty
     }
 }