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package org.daisy.pipeline.logging;

import ch.qos.logback.classic.Level;
import ch.qos.logback.classic.sift.MDCBasedDiscriminator;
import ch.qos.logback.classic.spi.ILoggingEvent;
import ch.qos.logback.core.AppenderBase;

import org.daisy.common.messaging.Message;
import org.daisy.common.messaging.MessageAppender;
import org.daisy.common.messaging.MessageBuilder;
import org.daisy.common.properties.Properties;

/**
 * Append to the current job progress thread.
 *
 * Configure like this:
 *
 * <appender name="JOB" class="org.daisy.pipeline.logging.JobProgressAppender">
 *   <filter class="org.daisy.pipeline.logging.ThresholdFilter">
 *     <rootLevel>INFO</rootLevel>
 *     <loggerLevels>
 *       cz.vutbr.web=WARN
 *       org.daisy.common.xproc.calabash.steps.Message=WARN
 *       com.xmlcalabash.runtime.XAtomicStep=WARN
 *     </loggerLevels>
 *   </filter>
 * </appender>
 */
public class JobProgressAppender extends AppenderBase {

	// Global threshold under which messages should be ignored. This filtering also happens on the
	// level of MessageAccessor, but doing it here also for further performance boost. The messages
	// created by this class do not carry any progress information and are immediately closed, so it
	// is safe to drop them completely (as opposed to hiding the text and promoting the child
	// messages). Note that in addition to this (global) threshold, other thresholds can be set
	// with ThresholdFilter.
	private static Message.Level messagesThreshold;
	static {
		try {
			messagesThreshold = Message.Level.valueOf(
				Properties.getProperty("org.daisy.pipeline.log.level", "INFO"));
		} catch (IllegalArgumentException e) {
			messagesThreshold = Message.Level.INFO;
		}
	}
	
	// MessageAppender.getActiveBlockLogger() can not be used here because the logback appender is
	// run in a separate thread. Using MDCBasedDiscriminator instead.
	private MDCBasedDiscriminator threadDiscriminator;

	@Override
	public void start() {
		threadDiscriminator = new MDCBasedDiscriminator();
		threadDiscriminator.setKey("message-thread");
		threadDiscriminator.setDefaultValue("default");
		super.start();
	}

	protected void append(ILoggingEvent event) {
		if (!isStarted())
			return;
		String threadId = threadDiscriminator.getDiscriminatingValue(event);
		if (!"default".equals(threadId)) {
			Message.Level level = messageLevelFromLogbackLevel(event.getLevel());
			if (!messagesThreshold.isMoreSevereThan(level)) {
				MessageAppender activeBlock = MessageAppender.getActiveBlock(threadId);
				// we need an active block otherwise we have no place to send the message to
				if (activeBlock != null) {
					activeBlock.append(
						new MessageBuilder()
						.withLevel(level)
						.withText(event.getFormattedMessage())
					).close();
				}
			}
		}
	}

	private static Message.Level messageLevelFromLogbackLevel(Level level) {
		switch(level.toInt()) {
		case Level.TRACE_INT:
			return Message.Level.TRACE;
		case Level.DEBUG_INT:
			return Message.Level.DEBUG;
		case Level.INFO_INT:
			return Message.Level.INFO;
		case Level.WARN_INT:
			return Message.Level.WARNING;
		case Level.ERROR_INT:
			return Message.Level.ERROR;
		case Level.ALL_INT:
		case Level.OFF_INT:
		default:
			return null; }
	}
}