/*

 * Copyright (C) 2015 - EfficiOS Inc., Alexandre Montplaisir <alexmonthy@efficios.com>

 *

 * This library is free software; you can redistribute it and/or modify it

 * under the terms of the GNU Lesser General Public License, version 2.1 only,

 * as published by the Free Software Foundation.

 *

 * This library is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License

 * for more details.

 *

 * You should have received a copy of the GNU Lesser General Public License

 * along with this library; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

 */

package org.lttng.ust.agent.log4j;

import java.util.Collection;

import java.util.Collections;

import java.util.Enumeration;

import java.util.List;

import java.util.Set;

import java.util.TreeSet;

import org.apache.log4j.Appender;

import org.apache.log4j.Category;

import org.apache.log4j.LogManager;

import org.apache.log4j.Logger;

import org.lttng.ust.agent.AbstractLttngAgent;

/**

 * Agent implementation for using the Log4j logger, connecting to a root session

 * daemon.

 *

 * @author Alexandre Montplaisir

 */

class LttngLog4jAgent extends AbstractLttngAgent<LttngLogAppender> {

	private static LttngLog4jAgent instance = null;

	private LttngLog4jAgent() {

		super(Domain.LOG4J);

	}

	public static synchronized LttngLog4jAgent getInstance() {

		if (instance == null) {

			instance = new LttngLog4jAgent();

		}

		return instance;

	}

	@Override

	public Collection<String> listAvailableEvents() {

		Set<String> ret = new TreeSet<String>();

		@SuppressWarnings("unchecked")

		List<Logger> loggers = Collections.list(LogManager.getCurrentLoggers());

		for (Logger logger : loggers) {

			if (logger == null) {

				continue;

			}

			/*

			 * Check if that logger has at least one LTTng log4j appender

			 * attached.

			 */

			if (hasLttngAppenderAttached(logger)) {

				ret.add(logger.getName());

			}

		}

		return ret;

	}

	private static boolean hasLttngAppenderAttached(Category logger) {

		@SuppressWarnings("unchecked")

		Enumeration<Appender> appenders = logger.getAllAppenders();

		if (appenders != null) {

			for (Appender appender : Collections.list(appenders)) {

				if (appender instanceof LttngLogAppender) {

					return true;

				}

			}

		}

		/*

		 * A parent logger, if any, may be connected to an LTTng handler. In

		 * this case, we will want to include this child logger in the output,

		 * since it will be accessible by LTTng.

		 */

		Category parent = logger.getParent();

		if (parent != null) {

			return hasLttngAppenderAttached(parent);

		}

		/*

		 * We have reached the root logger and have not found any LTTng handler,

		 * this event will not be accessible.

		 */

		return false;

	}

}