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Core services for Usergrid system.
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/*******************************************************************************
 * Copyright 2012 Apigee Corporation
 * 
 * Licensed 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.
 ******************************************************************************/
/*
 * Copyright 2010-2011 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Portions copyright 2006-2009 James Murty. Please see LICENSE.txt
 * for applicable license terms and NOTICE.txt for applicable notices.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 * 
 *  http://aws.amazon.com/apache2.0
 * 
 * or in the "license" file accompanying this file. This file 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.usergrid.utils;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import java.util.SimpleTimeZone;

/**
 * Utilities for parsing and formatting dates.
 * 
 * Note that this class doesn't use static methods because of the
 * synchronization issues with SimpleDateFormat. This lets synchronization be
 * done on a per-object level, instead of on a per-class level.
 */
public class DateUtils {

	/** ISO 8601 parser */
	protected final SimpleDateFormat iso8601DateParser = new SimpleDateFormat(
			"yyyy-MM-dd'T'HH:mm:ss.SSS'Z'");

	/** Alternate ISO 8601 parser without fractional seconds */
	protected final SimpleDateFormat alternateIo8601DateParser = new SimpleDateFormat(
			"yyyy-MM-dd'T'HH:mm:ss'Z'");

	/** RFC 822 parser */
	protected final SimpleDateFormat rfc822DateParser = new SimpleDateFormat(
			"EEE, dd MMM yyyy HH:mm:ss z", Locale.US);

	/**
	 * Constructs a new DateUtils object, ready to parse/format dates.
	 */
	public DateUtils() {
		iso8601DateParser.setTimeZone(new SimpleTimeZone(0, "GMT"));
		rfc822DateParser.setTimeZone(new SimpleTimeZone(0, "GMT"));
		alternateIo8601DateParser.setTimeZone(new SimpleTimeZone(0, "GMT"));
	}

	public static DateUtils instance = new DateUtils();

	/**
	 * Parses the specified date string as an ISO 8601 date and returns the Date
	 * object.
	 * 
	 * @param dateString
	 *            The date string to parse.
	 * 
	 * @return The parsed Date object.
	 * 
	 * @throws ParseException
	 *             If the date string could not be parsed.
	 */
	public Date parseIso8601Date(String dateString) throws ParseException {
		try {
			synchronized (iso8601DateParser) {
				return iso8601DateParser.parse(dateString);
			}
		} catch (ParseException e) {
			// If the first ISO 8601 parser didn't work, try the alternate
			// version which doesn't include fractional seconds
			synchronized (alternateIo8601DateParser) {
				return alternateIo8601DateParser.parse(dateString);
			}
		}
	}

	/**
	 * Formats the specified date as an ISO 8601 string.
	 * 
	 * @param date
	 *            The date to format.
	 * 
	 * @return The ISO 8601 string representing the specified date.
	 */
	public String formatIso8601Date(Date date) {
		synchronized (iso8601DateParser) {
			return iso8601DateParser.format(date);
		}
	}

	public String iso8601DateNow() {
		return formatIso8601Date(new Date());
	}

	/**
	 * Formats the specified date as an RFC 822 string.
	 * 
	 * @param date
	 *            The date to format.
	 * 
	 * @return The RFC 822 string representing the specified date.
	 */
	public String formatRfc822Date(Date date) {
		synchronized (rfc822DateParser) {
			return rfc822DateParser.format(date);
		}
	}

	/**
	 * Parses the specified date string as an RFC 822 date and returns the Date
	 * object.
	 * 
	 * @param dateString
	 *            The date string to parse.
	 * 
	 * @return The parsed Date object.
	 * 
	 * @throws ParseException
	 *             If the date string could not be parsed.
	 */
	public Date parseRfc822Date(String dateString) throws ParseException {
		synchronized (rfc822DateParser) {
			return rfc822DateParser.parse(dateString);
		}
	}

}