/*
 * Copyright (c) 2010, 2019 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package org.glassfish.jersey.message.internal;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Arrays;
import java.util.Collections;
import java.util.Date;
import java.util.List;
import java.util.Locale;
import java.util.TimeZone;

Helper class for HTTP specified date formats.
Author:
Paul Sandoz, Marek Potociar/**
 * Helper class for HTTP specified date formats.
 *
 * @author Paul Sandoz
 * @author Marek Potociar
 */
public final class HttpDateFormat {

    private HttpDateFormat() {
    }
    
The date format pattern for RFC 1123.
/**
     * The date format pattern for RFC 1123.
     */
    private static final String RFC1123_DATE_FORMAT_PATTERN = "EEE, dd MMM yyyy HH:mm:ss zzz";
    
The date format pattern for RFC 1036.
/**
     * The date format pattern for RFC 1036.
     */
    private static final String RFC1036_DATE_FORMAT_PATTERN = "EEEE, dd-MMM-yy HH:mm:ss zzz";
    
The date format pattern for ANSI C asctime().
/**
     * The date format pattern for ANSI C asctime().
     */
    private static final String ANSI_C_ASCTIME_DATE_FORMAT_PATTERN = "EEE MMM d HH:mm:ss yyyy";

    private static final TimeZone GMT_TIME_ZONE = TimeZone.getTimeZone("GMT");

    private static final ThreadLocal<List<SimpleDateFormat>> dateFormats = new ThreadLocal<List<SimpleDateFormat>>() {

        @Override
        protected synchronized List<SimpleDateFormat> initialValue() {
            return createDateFormats();
        }
    };

    private static List<SimpleDateFormat> createDateFormats() {
        final SimpleDateFormat[] formats = new SimpleDateFormat[]{
            new SimpleDateFormat(RFC1123_DATE_FORMAT_PATTERN, Locale.US),
            new SimpleDateFormat(RFC1036_DATE_FORMAT_PATTERN, Locale.US),
            new SimpleDateFormat(ANSI_C_ASCTIME_DATE_FORMAT_PATTERN, Locale.US)
        };
        formats[0].setTimeZone(GMT_TIME_ZONE);
        formats[1].setTimeZone(GMT_TIME_ZONE);
        formats[2].setTimeZone(GMT_TIME_ZONE);

        return Collections.unmodifiableList(Arrays.asList(formats));
    }

    
Return an unmodifiable list of HTTP specified date formats to use for parsing or formatting Date. 

The list of date formats are scoped to the current thread and may be
used without requiring to synchronize access to the instances when
parsing or formatting.
Returns:
the list of data formats./**
     * Return an unmodifiable list of HTTP specified date formats to use for
     * parsing or formatting {@link Date}.
     * <p>
     * The list of date formats are scoped to the current thread and may be
     * used without requiring to synchronize access to the instances when
     * parsing or formatting.
     *
     * @return the list of data formats.
     */
    private static List<SimpleDateFormat> getDateFormats() {
        return dateFormats.get();
    }

    
Get the preferred HTTP specified date format (RFC 1123).

The date format is scoped to the current thread and may be
used without requiring to synchronize access to the instance when
parsing or formatting.
Returns:
the preferred of data format./**
     * Get the preferred HTTP specified date format (RFC 1123).
     * <p>
     * The date format is scoped to the current thread and may be
     * used without requiring to synchronize access to the instance when
     * parsing or formatting.
     *
     * @return the preferred of data format.
     */
    public static SimpleDateFormat getPreferredDateFormat() {
        // returns clone because calling SDF.parse(...) can change time zone
        return (SimpleDateFormat) dateFormats.get().get(0).clone();
    }

    
Read a date.
Params:
date – the date as a string.
Throws:
ParseException – in case the date string cannot be parsed.
Returns:
the date/**
     * Read a date.
     *
     * @param date the date as a string.
     *
     * @return the date
     * @throws java.text.ParseException in case the date string cannot be parsed.
     */
    public static Date readDate(final String date) throws ParseException {
        ParseException pe = null;
        for (final SimpleDateFormat f : HttpDateFormat.getDateFormats()) {
            try {
                Date result = f.parse(date);
                // parse can change time zone -> set it back to GMT
                f.setTimeZone(GMT_TIME_ZONE);
                return result;
            } catch (final ParseException e) {
                pe = (pe == null) ? e : pe;
            }
        }

        throw pe;
    }
}