import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.text.MessageFormat;

/**
 * Contains methods to access and manipulate logback framework dynamically at run-time. Here 'dynamically' means without
 * referencing the logback JAR, but using it if found in the classpath.
 *
 * @author Muhammed Demirbas
 * @since 19 Mar 2013
 */
public final class LogbackUtils
{
    	public  static final String LOGBACK_CLASSIC        = "ch.qos.logback.classic";
	public  static final String LOGBACK_CLASSIC_LOGGER = "ch.qos.logback.classic.Logger";
	public  static final String LOGBACK_CLASSIC_LEVEL  = "ch.qos.logback.classic.Level";
	private static final Logger logger                 = LoggerFactory.getLogger(LogbackUtils.class);

	private LogbackUtils()
	{
		// Prevent instance creation
	}

	/**
	 * Dynamically sets the logback log level for the given class to the specified level.
	 *
	 * @param loggerName Name of the logger to set its log level. If blank, root logger will be used.
	 * @param logLevel   One of the supported log levels: TRACE, DEBUG, INFO, WARN, ERROR, FATAL,
	 *                      OFF. {@code null} value is considered as 'OFF'.
	 */
	public static boolean setLogLevel(String loggerName, String logLevel)
	{
		String logLevelUpper = (logLevel == null) ? "OFF" : logLevel.toUpperCase();

		try
		{
			Package logbackPackage = Package.getPackage(LOGBACK_CLASSIC);
			if (logbackPackage == null)
			{
				logger.info("Logback is not in the classpath!");
				return false;
			}

			// Use ROOT logger if given logger name is blank.
			if ((loggerName == null) || loggerName.trim().isEmpty())
			{
				loggerName = (String) getFieldVaulue(LOGBACK_CLASSIC_LOGGER, "ROOT_LOGGER_NAME");
			}

			// Obtain logger by the name
			Logger loggerObtained = LoggerFactory.getLogger(loggerName);
			if (loggerObtained == null)
			{
				// I don't know if this case occurs
				logger.warn("No logger for the name: {}", loggerName);
				return false;
			}

			Object logLevelObj = getFieldVaulue(LOGBACK_CLASSIC_LEVEL, logLevelUpper);
			if (logLevelObj == null)
			{
				logger.warn("No such log level: {}", logLevelUpper);
				return false;
			}

			Class<?>[] paramTypes =  { logLevelObj.getClass() };
			Object[]   params     =  { logLevelObj };

			Class<?> clz    = Class.forName(LOGBACK_CLASSIC_LOGGER);
			Method   method = clz.getMethod("setLevel", paramTypes);
			method.invoke(loggerObtained, params);

			logger.debug("Log level set to {} for the logger '{}'", logLevelUpper, loggerName);
			return true;
		}
		catch (Exception e)
		{
			logger.warn("Couldn't set log level to {} for the logger '{}'", logLevelUpper, loggerName, e);
			return false;
		}
	}

	private static Object getFieldVaulue(String fullClassName, String fieldName)
	{
		try
		{
			Class<?> clazz = Class.forName(fullClassName);
			Field    field = clazz.getField(fieldName);
			return field.get(null);
		}
		catch (ClassNotFoundException | IllegalAccessException | IllegalArgumentException | NoSuchFieldException |
				SecurityException ignored)
		{
			return null;
		}
	}
}