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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.log4j.pattern;

import org.apache.log4j.spi.LoggingEvent;

/**
 * Return the relative time in milliseconds since loading of the LoggingEvent
 * class.
 *
 * @author Ceki Gülcü
 */
public class RelativeTimePatternConverter extends LoggingEventPatternConverter {
    /**
     * Cached formatted timestamp.
     */
    private CachedTimestamp lastTimestamp = new CachedTimestamp(0, "");

    /**
     * Private constructor.
     */
    public RelativeTimePatternConverter() {
	super("Time", "time");
    }

    /**
     * Obtains an instance of RelativeTimePatternConverter.
     * 
     * @param options options, currently ignored, may be null.
     * @return instance of RelativeTimePatternConverter.
     */
    public static RelativeTimePatternConverter newInstance(final String[] options) {
	return new RelativeTimePatternConverter();
    }

    /**
     * {@inheritDoc}
     */
    public void format(final LoggingEvent event, final StringBuffer toAppendTo) {
	long timestamp = event.timeStamp;

	if (!lastTimestamp.format(timestamp, toAppendTo)) {
	    final String formatted = Long.toString(timestamp - LoggingEvent.getStartTime());
	    toAppendTo.append(formatted);
	    lastTimestamp = new CachedTimestamp(timestamp, formatted);
	}
    }

    /**
     * Cached timestamp and formatted value.
     */
    private static final class CachedTimestamp {
	/**
	 * Cached timestamp.
	 */
	private final long timestamp;

	/**
	 * Cached formatted timestamp.
	 */
	private final String formatted;

	/**
	 * Creates a new instance.
	 * 
	 * @param timestamp timestamp.
	 * @param formatted formatted timestamp.
	 */
	public CachedTimestamp(long timestamp, final String formatted) {
	    this.timestamp = timestamp;
	    this.formatted = formatted;
	}

	/**
	 * Appends the cached formatted timestamp to the buffer if timestamps match.
	 * 
	 * @param newTimestamp requested timestamp.
	 * @param toAppendTo   buffer to append formatted timestamp.
	 * @return true if requested timestamp matched cached timestamp.
	 */
	public boolean format(long newTimestamp, final StringBuffer toAppendTo) {
	    if (newTimestamp == timestamp) {
		toAppendTo.append(formatted);

		return true;
	    }

	    return false;
	}
    }
}