/**
 * Logback: the reliable, generic, fast and flexible logging framework.
 * Copyright (C) 1999-2015, QOS.ch. All rights reserved.
 *
 * This program and the accompanying materials are dual-licensed under
 * either the terms of the Eclipse Public License v1.0 as published by
 * the Eclipse Foundation
 *
 *   or (per the licensee's choosing)
 *
 * under the terms of the GNU Lesser General Public License version 2.1
 * as published by the Free Software Foundation.
 */
package ch.qos.logback.core.util;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;

/**
 * A synchronized implementation of  SimpleDateFormat which uses caching internally.
 *
 * @author Ceki Gülcü
 * @since 0.9.29
 */
public class CachingDateFormatter {

    long lastTimestamp = -1;
    String cachedStr = null;
    final SimpleDateFormat sdf;

    public CachingDateFormatter(String pattern) {
        sdf = new SimpleDateFormat(pattern);
    }

    public final String format(long now) {

        // SimpleDateFormat is not thread safe.

        // See also the discussion in http://jira.qos.ch/browse/LBCLASSIC-36
        // DateFormattingThreadedThroughputCalculator and SelectiveDateFormattingRunnable
        // are also noteworthy

        // The now == lastTimestamp guard minimizes synchronization
        synchronized (this) {
            if (now != lastTimestamp) {
                lastTimestamp = now;
                cachedStr = sdf.format(new Date(now));
            }
            return cachedStr;
        }
    }

    public void setTimeZone(TimeZone tz) {
        sdf.setTimeZone(tz);
    }
}