package edu.hws.eck.mdb;

import java.util.Locale;
import java.util.ResourceBundle;
import java.text.MessageFormat;

/**
 * This class provides some support for Internationalization, making it possible
 * to easily get a String corresponding to a key in a properties file, using the
 * method I18n.tr().  A method is also provided to change the locale.
 */
public class I18n {
    
    /**
     * The base name for the properties files for this program.  The default
     * properties file name is strings.properties in the directory edu/hws/eck/mdb.
     * Property files for other locales would have the form strings_xx.properties
     * where xx is the code for the locale.  To use this file in another program,
     * only the propertyFileName has to be changed.
     */
    private final static String propertyFileName = "edu.hws.eck.mdb.strings";
    
    /**
     * If locale is null, the default locale is used.  A non-null value can be
     * set by calling setLocale() or setLocaleName() to use a non-default locale.
     */
    private static Locale locale;
    
    /**
     * The resource bundle that is created from the properties file.
     */
    private static ResourceBundle translations;
    
    /**
     * Look up a key string in the properties file to find its translation.  If no
     * translation is found or any other error occurs, the key string is returned
     * unmodified.
     * @param key the key string.
     * @param args if the value string associated with the key contains placeholders 
     *   {0}, {1}, {2}, ...,  then the values of the optional args parameters are substituted
     *   for the placeholders. 
     * @return the value associated to key in the properties files, with placeholders replaced
     *   by args if appropriate; if any error occurs, the key string is returned.
     */
    public static String tr(String key, Object... args) {
        if (translations == null)
            loadStrings();
        if (translations == null)
            return key;
        try {
            String str = translations.getString(key);
            return MessageFormat.format(str,args);
        }
        catch (Exception e) {
            return key;
        }
    }
    
    /**
     * Same as tr(), except that when an error occurs, the return value is null.
     */
    public static String trIfFound(String key, Object... args) {
        if (translations == null)
            loadStrings();
        if (translations == null)
            return null;
        try {
            String str = translations.getString(key);
            return MessageFormat.format(str,args);
        }
        catch (Exception e) {
            return null;
        }
    }
    
    /**
     * Specifies a locale to use for translations in future calls to I18n.tr().
     * (This does not, of course, affect any strings that have already been
     * translated already.)
     * @param newLocale the locale to use, or null to use the default locale
     */
    public static void setLocale(Locale newLocale) {
        if ( (locale == null && newLocale != null )
                || (locale != null && !locale.equals(newLocale)) ) {
            locale = newLocale;
            translations = null; // forces loading of a new resource bundle
        }
    }
    
    /**
     * Convenience method calls setLocale(new Locale(localeLanguageCode)).
     * This would be used, for example, as I18n.setLanguage("fr");
     * @param localeLanguageCode the two-letter language code for the locale
     */
    public static void setLanguage(String localeLanguageCode) {
        setLocale(new Locale(localeLanguageCode));
    }
    
    /**
     * Used for loading the resource bundle.  If it can't be loaded, then
     * the bundle will be null after this method returns.
     */
    private static void loadStrings() {
        if (locale != null) {
            try {
                translations = ResourceBundle.getBundle(propertyFileName, locale);
                return;
            }
            catch (Exception e) {
            }
        }
        try {
            translations = ResourceBundle.getBundle(propertyFileName);
        }
        catch (Exception e) {
            translations = null;
        }
    }
    
    /**
     * Declaring a private constructor makes sure that no one will be
     * able to create instances of this class.  Everything in this
     * class is static, so there is no reason to create an I18n object.
     */
    private I18n() {
    }
    
}