/*******************************************************************************
 * Copyright (c) 2015, 2016 Obeo.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Obeo - initial API and implementation
 *******************************************************************************/
package org.eclipse.eef.common.api.utils;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.security.AccessController;
import java.security.PrivilegedAction;

import org.eclipse.emf.common.EMFPlugin;

/**
 * Helper class with bundle-independent code, that can be reused by other I18N classes local to each plug-in.
 *
 * @author pcdavid
 */
public final class I18N {
	/**
	 * Used to mark a {@code public static String} field of a class as an externalized string, whose actual value will
	 * depend on the locale used at runtime. The optional value corresponds to the key in the {@code ResourceLocator};
	 * if absent, the name of the field itself is used as key.
	 *
	 * @author pcdavid
	 */
	@Retention(RetentionPolicy.RUNTIME)
	@Target(ElementType.FIELD)
	public @interface TranslatableMessage {
		/**
		 * The (optional) value of the message key. If absent, the key is assumed to be the same as the Java field's
		 * name.
		 *
		 * @return the message key, if different from the field name.
		 */
		String[] value() default {};
	}

	/**
	 * The constructor.
	 */
	private I18N() {
		// Prevent instantiation
	}

	/**
	 * Initializes the value of a class's {@code TranslatableMessage}s using the specified plugin as
	 * {@code ResourceLocator}.
	 *
	 * @param messagesClass
	 *            the class which defines the fields to initialize.
	 * @param plugin
	 *            the plugin from which to obtain the localized value of the fields.
	 */
	public static void initializeMessages(final Class<?> messagesClass, final EMFPlugin plugin) {
		if (System.getSecurityManager() == null) {
			load(plugin, messagesClass);
			return;
		}
		AccessController.doPrivileged(new PrivilegedAction<Void>() {
			@Override
			public Void run() {
				load(plugin, messagesClass);
				return null;
			}
		});
	}

	/**
	 * Loads the message class with the given {@link EMFPlugin}.
	 *
	 * @param plugin
	 *            The plugin
	 * @param messagesClass
	 *            The message class
	 */
	private static void load(EMFPlugin plugin, Class<?> messagesClass) {
		for (Field field : messagesClass.getDeclaredFields()) {
			if (isMessageField(field)) {
				initialize(field, plugin);
			}
		}
	}

	/**
	 * Indicates if the given field is a message field.
	 *
	 * @param field
	 *            The field
	 * @return <code>true</code> if the given field is a message field, <code>false</code> otherwise.
	 */
	private static boolean isMessageField(Field field) {
		int mods = field.getModifiers();
		boolean modsOK = Modifier.isPublic(mods) && Modifier.isStatic(mods) && !Modifier.isFinal(mods);
		return modsOK && field.isAnnotationPresent(I18N.TranslatableMessage.class) && field.getType() == String.class;
	}

	/**
	 * Initializes the given field used the plugin.
	 *
	 * @param field
	 *            The field to initialize
	 * @param plugin
	 *            The plugin
	 */
	private static void initialize(Field field, EMFPlugin plugin) {
		String key = getKey(field);
		String value = plugin.getString(key);
		if (!field.isAccessible()) {
			field.setAccessible(true);
		}
		try {
			field.set(null, value);
		} catch (IllegalArgumentException e) {
			plugin.log(e);
		} catch (IllegalAccessException e) {
			plugin.log(e);
		}
	}

	/**
	 * Returns the key for the given field.
	 *
	 * @param field
	 *            The field
	 * @return The key of the field
	 */
	private static String getKey(Field field) {
		I18N.TranslatableMessage annot = field.getAnnotation(I18N.TranslatableMessage.class);
		String[] key = annot.value();
		if (key == null || key.length == 0) {
			key = new String[] { field.getName() };
		}
		return key[0];
	}
}