/*
 * ====================================================================
 * 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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */

package org.apache.http.client.utils;

import java.lang.ref.SoftReference;
import java.text.ParsePosition;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import java.util.TimeZone;

import org.apache.http.util.Args;

A utility class for parsing and formatting HTTP dates as used in cookies and
other headers.  This class handles dates as defined by RFC 2616 section
3.3.1 as well as some other common non-standard formats.
Since:
4.3/**
 * A utility class for parsing and formatting HTTP dates as used in cookies and
 * other headers.  This class handles dates as defined by RFC 2616 section
 * 3.3.1 as well as some other common non-standard formats.
 *
 * @since 4.3
 */
public final class DateUtils {

    
Date format pattern used to parse HTTP date headers in RFC 1123 format.
/**
     * Date format pattern used to parse HTTP date headers in RFC 1123 format.
     */
    public static final String PATTERN_RFC1123 = "EEE, dd MMM yyyy HH:mm:ss zzz";

    
Date format pattern used to parse HTTP date headers in RFC 1036 format.
/**
     * Date format pattern used to parse HTTP date headers in RFC 1036 format.
     */
    public static final String PATTERN_RFC1036 = "EEE, dd-MMM-yy HH:mm:ss zzz";

    
Date format pattern used to parse HTTP date headers in ANSI C asctime() format. /**
     * Date format pattern used to parse HTTP date headers in ANSI C
     * {@code asctime()} format.
     */
    public static final String PATTERN_ASCTIME = "EEE MMM d HH:mm:ss yyyy";

    private static final String[] DEFAULT_PATTERNS = new String[] {
        PATTERN_RFC1123,
        PATTERN_RFC1036,
        PATTERN_ASCTIME
    };

    private static final Date DEFAULT_TWO_DIGIT_YEAR_START;

    public static final TimeZone GMT = TimeZone.getTimeZone("GMT");

    static {
        final Calendar calendar = Calendar.getInstance();
        calendar.setTimeZone(GMT);
        calendar.set(2000, Calendar.JANUARY, 1, 0, 0, 0);
        calendar.set(Calendar.MILLISECOND, 0);
        DEFAULT_TWO_DIGIT_YEAR_START = calendar.getTime();
    }

    
Parses a date value.  The formats used for parsing the date value are retrieved from
the default http params.
Params:
dateValue – the date value to parse
Returns:
the parsed date or null if input could not be parsed/**
     * Parses a date value.  The formats used for parsing the date value are retrieved from
     * the default http params.
     *
     * @param dateValue the date value to parse
     *
     * @return the parsed date or null if input could not be parsed
     */
    public static Date parseDate(final String dateValue) {
        return parseDate(dateValue, null, null);
    }

    
Parses the date value using the given date formats.
Params:
dateValue – the date value to parse
dateFormats – the date formats to use
Returns:
the parsed date or null if input could not be parsed/**
     * Parses the date value using the given date formats.
     *
     * @param dateValue the date value to parse
     * @param dateFormats the date formats to use
     *
     * @return the parsed date or null if input could not be parsed
     */
    public static Date parseDate(final String dateValue, final String[] dateFormats) {
        return parseDate(dateValue, dateFormats, null);
    }

    
Parses the date value using the given date formats.
Params:
dateValue – the date value to parse
dateFormats – the date formats to use
startDate – During parsing, two digit years will be placed in the range startDate to startDate + 100 years. This value may be null. When null is given as a parameter, year 2000 will be used.
Returns:
the parsed date or null if input could not be parsed/**
     * Parses the date value using the given date formats.
     *
     * @param dateValue the date value to parse
     * @param dateFormats the date formats to use
     * @param startDate During parsing, two digit years will be placed in the range
     * {@code startDate} to {@code startDate + 100 years}. This value may
     * be {@code null}. When {@code null} is given as a parameter, year
     * {@code 2000} will be used.
     *
     * @return the parsed date or null if input could not be parsed
     */
    public static Date parseDate(
            final String dateValue,
            final String[] dateFormats,
            final Date startDate) {
        Args.notNull(dateValue, "Date value");
        final String[] localDateFormats = dateFormats != null ? dateFormats : DEFAULT_PATTERNS;
        final Date localStartDate = startDate != null ? startDate : DEFAULT_TWO_DIGIT_YEAR_START;
        String v = dateValue;
        // trim single quotes around date if present
        // see issue #5279
        if (v.length() > 1 && v.startsWith("'") && v.endsWith("'")) {
            v = v.substring (1, v.length() - 1);
        }

        for (final String dateFormat : localDateFormats) {
            final SimpleDateFormat dateParser = DateFormatHolder.formatFor(dateFormat);
            dateParser.set2DigitYearStart(localStartDate);
            final ParsePosition pos = new ParsePosition(0);
            final Date result = dateParser.parse(v, pos);
            if (pos.getIndex() != 0) {
                return result;
            }
        }
        return null;
    }

    
Formats the given date according to the RFC 1123 pattern.
Params:
date – The date to format.
See Also:
PATTERN_RFC1123
Returns:
An RFC 1123 formatted date string./**
     * Formats the given date according to the RFC 1123 pattern.
     *
     * @param date The date to format.
     * @return An RFC 1123 formatted date string.
     *
     * @see #PATTERN_RFC1123
     */
    public static String formatDate(final Date date) {
        return formatDate(date, PATTERN_RFC1123);
    }

    
Formats the given date according to the specified pattern. The pattern must conform to that used by the simple date
format class. 
Params:
date – The date to format.
pattern – The pattern to use for formatting the date.
Throws:
IllegalArgumentException – If the given date pattern is invalid.
See Also:
SimpleDateFormat
Returns:
A formatted date string./**
     * Formats the given date according to the specified pattern.  The pattern
     * must conform to that used by the {@link SimpleDateFormat simple date
     * format} class.
     *
     * @param date The date to format.
     * @param pattern The pattern to use for formatting the date.
     * @return A formatted date string.
     *
     * @throws IllegalArgumentException If the given date pattern is invalid.
     *
     * @see SimpleDateFormat
     */
    public static String formatDate(final Date date, final String pattern) {
        Args.notNull(date, "Date");
        Args.notNull(pattern, "Pattern");
        final SimpleDateFormat formatter = DateFormatHolder.formatFor(pattern);
        return formatter.format(date);
    }

    
Clears thread-local variable containing DateFormat cache. 
Since:
4.3/**
     * Clears thread-local variable containing {@link java.text.DateFormat} cache.
     *
     * @since 4.3
     */
    public static void clearThreadLocal() {
        DateFormatHolder.clearThreadLocal();
    }

    
This class should not be instantiated. /** This class should not be instantiated. */
    private DateUtils() {
    }

    
A factory for SimpleDateFormats. The instances are stored in a threadlocal way because SimpleDateFormat is not threadsafe as noted in its javadoc. /**
     * A factory for {@link SimpleDateFormat}s. The instances are stored in a
     * threadlocal way because SimpleDateFormat is not threadsafe as noted in
     * {@link SimpleDateFormat its javadoc}.
     *
     */
    final static class DateFormatHolder {

        private static final ThreadLocal<SoftReference<Map<String, SimpleDateFormat>>>
            THREADLOCAL_FORMATS = new ThreadLocal<SoftReference<Map<String, SimpleDateFormat>>>();

        
creates a SimpleDateFormat for the requested format string. 
Params:
pattern –  a non-null format String according to SimpleDateFormat. The format is not checked against null since all paths go through DateUtils.
Returns:
the requested format. This simple dateformat should not be used to apply to a different pattern./**
         * creates a {@link SimpleDateFormat} for the requested format string.
         *
         * @param pattern
         *            a non-{@code null} format String according to
         *            {@link SimpleDateFormat}. The format is not checked against
         *            {@code null} since all paths go through
         *            {@link DateUtils}.
         * @return the requested format. This simple dateformat should not be used
         *         to {@link SimpleDateFormat#applyPattern(String) apply} to a
         *         different pattern.
         */
        public static SimpleDateFormat formatFor(final String pattern) {
            final SoftReference<Map<String, SimpleDateFormat>> ref = THREADLOCAL_FORMATS.get();
            Map<String, SimpleDateFormat> formats = ref == null ? null : ref.get();
            if (formats == null) {
                formats = new HashMap<String, SimpleDateFormat>();
                THREADLOCAL_FORMATS.set(
                        new SoftReference<Map<String, SimpleDateFormat>>(formats));
            }

            SimpleDateFormat format = formats.get(pattern);
            if (format == null) {
                format = new SimpleDateFormat(pattern, Locale.US);
                format.setTimeZone(TimeZone.getTimeZone("GMT"));
                formats.put(pattern, format);
            }

            return format;
        }

        public static void clearThreadLocal() {
            THREADLOCAL_FORMATS.remove();
        }

    }

}