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/*
 * #%L
 * fujion
 * %%
 * Copyright (C) 2018 Fujion Framework
 * %%
 * Licensed 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.
 *
 * #L%
 */
package org.fujion.common;

import java.util.ArrayList;
import java.util.List;
import java.util.Locale;
import java.util.TimeZone;

/**
 * Provides localization support.
 */
public class Localizer {
    
    /**
     * Source of localized messages.
     */
    public interface IMessageSource {
        
        /**
         * Retrieve a message for the specified locale given its id.
         *
         * @param id The message identifier.
         * @param locale The locale.
         * @param args Optional message arguments.
         * @return A fully formatted message, or null if none was found.
         */
        String getMessage(String id, Locale locale, Object... args);
        
    }
    
    /**
     * Resolves the default locale.
     */
    public interface ILocaleResolver {
        
        /**
         * Returns the default locale when none is specified.
         *
         * @return The default locale
         */
        Locale getLocale();
    }
    
    /**
     * Interface for accessing the current time zone
     */
    public interface ITimeZoneResolver {
        
        /**
         * Returns the current time zone.
         *
         * @return TimeZone instance
         */
        TimeZone getTimeZone();
        
    }
    
    private static final Logger log = Logger.create(Localizer.class);
    
    private static final List messageSources = new ArrayList<>();
    
    private static ILocaleResolver localeResolver = () -> {
        return Locale.getDefault();
    };
    
    private static ITimeZoneResolver timeZoneResolver = () -> {
        return TimeZone.getDefault();
    };
    
    /**
     * Registers a message source for resolving messages.
     *
     * @param messageSource The message source.
     */
    public static void registerMessageSource(IMessageSource messageSource) {
        messageSources.add(messageSource);
    }
    
    /**
     * Returns a formatted message given a label identifier. Recognizes line continuation with
     * backslash characters.
     *
     * @param id A label identifier.
     * @param locale The locale. If null, uses the default locale.
     * @param args Optional replaceable parameters.
     * @return The formatted label.
     */
    public static String getMessage(String id, Locale locale, Object... args) {
        locale = locale == null ? getDefaultLocale() : locale;
        
        for (IMessageSource messageSource : messageSources) {
            try {
                return messageSource.getMessage(id, locale, args).replace("\\\n", "");
            } catch (Exception e) {
                // Ignore and try next message source.
            }
        }
        // Failing resolution, just return null.
        log.warn(() -> "Label not found for identifier: " + id);
        return null;
    }
    
    /**
     * Returns the default locale.
     *
     * @return The default locale.
     */
    public static Locale getDefaultLocale() {
        return localeResolver.getLocale();
    }
    
    /**
     * Sets the resolver used to determine the default locale.
     *
     * @param localeResolver An ILocaleResolver implementation.
     */
    public static void setLocaleResolver(ILocaleResolver localeResolver) {
        Localizer.localeResolver = localeResolver;
    }
    
    /**
     * Returns the local time zone.
     *
     * @return The local time zone.
     */
    public static TimeZone getTimeZone() {
        return timeZoneResolver.getTimeZone();
    }
    
    /**
     * Sets the resolver used to determine the local time zone.
     *
     * @param timeZoneResolver An ITimeZoneResolver implementation.
     */
    public static void setTimeZoneResolver(ITimeZoneResolver timeZoneResolver) {
        Localizer.timeZoneResolver = timeZoneResolver;
    }
    
    /**
     * Enforce static class.
     */
    private Localizer() {
    }
    
}