/*
 * 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.lang;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Set;

/**
 * <p>Operations to assist when working with a {@link Locale}.</p>
 *
 * <p>This class tries to handle <code>null</code> input gracefully.
 * An exception will not be thrown for a <code>null</code> input.
 * Each method documents its behaviour in more detail.</p>
 *
 * @author Apache Software Foundation
 * @since 2.2
 * @version $Id: LocaleUtils.java 911968 2010-02-19 20:26:21Z niallp $
 */
public class LocaleUtils {

    /** Unmodifiable list of available locales. */
    private static List cAvailableLocaleList; // lazily created by availableLocaleList()

    /** Unmodifiable set of available locales. */
    private static Set cAvailableLocaleSet;   // lazily created by availableLocaleSet()

    /** Unmodifiable map of language locales by country. */
    private static final Map cLanguagesByCountry = Collections.synchronizedMap(new HashMap());

    /** Unmodifiable map of country locales by language. */
    private static final Map cCountriesByLanguage = Collections.synchronizedMap(new HashMap());

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

    //-----------------------------------------------------------------------
    /**
     * <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("en")         = new Locale("en", "")
     *   LocaleUtils.toLocale("en_GB")      = new Locale("en", "GB")
     *   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
     */
    public static Locale toLocale(String str) {
        if (str == null) {
            return null;
        }
        int len = str.length();
        if (len != 2 && len != 5 && len < 7) {
            throw new IllegalArgumentException("Invalid locale format: " + str);
        }
        char ch0 = str.charAt(0);
        char ch1 = str.charAt(1);
        if (ch0 < 'a' || ch0 > 'z' || ch1 < 'a' || ch1 > 'z') {
            throw new IllegalArgumentException("Invalid locale format: " + str);
        }
        if (len == 2) {
            return new Locale(str, "");
        } else {
            if (str.charAt(2) != '_') {
                throw new IllegalArgumentException("Invalid locale format: " + str);
            }
            char ch3 = str.charAt(3);
            if (ch3 == '_') {
                return new Locale(str.substring(0, 2), "", str.substring(4));
            }
            char ch4 = str.charAt(4);
            if (ch3 < 'A' || ch3 > 'Z' || ch4 < 'A' || ch4 > 'Z') {
                throw new IllegalArgumentException("Invalid locale format: " + str);
            }
            if (len == 5) {
                return new Locale(str.substring(0, 2), str.substring(3, 5));
            } else {
                if (str.charAt(5) != '_') {
                    throw new IllegalArgumentException("Invalid locale format: " + str);
                }
                return new Locale(str.substring(0, 2), str.substring(3, 5), str.substring(6));
            }
        }
    }

    //-----------------------------------------------------------------------
    /**
     * <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, never null
     */
    public static List localeLookupList(Locale locale) {
        return localeLookupList(locale, locale);
    }

    //-----------------------------------------------------------------------
    /**
     * <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, never null
     */
    public static List localeLookupList(Locale locale, Locale defaultLocale) {
        List 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(), ""));
            }
            if (list.contains(defaultLocale) == false) {
                list.add(defaultLocale);
            }
        }
        return Collections.unmodifiableList(list);
    }

    //-----------------------------------------------------------------------
    /**
     * <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 availableLocaleList() {
        if(cAvailableLocaleList == null) { 
            initAvailableLocaleList(); 
        }
        return cAvailableLocaleList;
    }

    /**
     * Initializes the availableLocaleList. It is separate from availableLocaleList() 
     * to avoid the synchronized block affecting normal use, yet synchronized and 
     * lazy loading to avoid a static block affecting other methods in this class. 
     */
    private static synchronized void initAvailableLocaleList() {
        if(cAvailableLocaleList == null) {
            List list = Arrays.asList(Locale.getAvailableLocales());
            cAvailableLocaleList = Collections.unmodifiableList(list);
        }
    }

    //-----------------------------------------------------------------------
    /**
     * <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 availableLocaleSet() {
        if(cAvailableLocaleSet == null) { 
            initAvailableLocaleSet(); 
        }
        return cAvailableLocaleSet;
    }

    /**
     * Initializes the availableLocaleSet. It is separate from availableLocaleSet() 
     * to avoid the synchronized block affecting normal use, yet synchronized and 
     * lazy loading to avoid a static block affecting other methods in this class. 
     */
    private static synchronized void initAvailableLocaleSet() {
        if(cAvailableLocaleSet == null) {
            cAvailableLocaleSet = Collections.unmodifiableSet( new HashSet(availableLocaleList()) );
        }
    }

    //-----------------------------------------------------------------------
    /**
     * <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(Locale locale) {
        return availableLocaleList().contains(locale);
    }

    //-----------------------------------------------------------------------
    /**
     * <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, never null
     */
    public static List languagesByCountry(String countryCode) {
        List langs = (List) cLanguagesByCountry.get(countryCode);  //syncd
        if (langs == null) {
            if (countryCode != null) {
                langs = new ArrayList();
                List locales = availableLocaleList();
                for (int i = 0; i < locales.size(); i++) {
                    Locale locale = (Locale) locales.get(i);
                    if (countryCode.equals(locale.getCountry()) &&
                            locale.getVariant().length() == 0) {
                        langs.add(locale);
                    }
                }
                langs = Collections.unmodifiableList(langs);
            } else {
                langs = Collections.EMPTY_LIST;
            }
            cLanguagesByCountry.put(countryCode, langs);  //syncd
        }
        return langs;
    }

    //-----------------------------------------------------------------------
    /**
     * <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, never null
     */
    public static List countriesByLanguage(String languageCode) {
        List countries = (List) cCountriesByLanguage.get(languageCode);  //syncd
        if (countries == null) {
            if (languageCode != null) {
                countries = new ArrayList();
                List locales = availableLocaleList();
                for (int i = 0; i < locales.size(); i++) {
                    Locale locale = (Locale) locales.get(i);
                    if (languageCode.equals(locale.getLanguage()) &&
                            locale.getCountry().length() != 0 &&
                            locale.getVariant().length() == 0) {
                        countries.add(locale);
                    }
                }
                countries = Collections.unmodifiableList(countries);
            } else {
                countries = Collections.EMPTY_LIST;
            }
            cCountriesByLanguage.put(languageCode, countries);  //syncd
        }
        return countries;
    }

}
