/*
 * $HeadURL: http://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk/module-client/src/main/java/org/apache/http/impl/cookie/DateUtils.java $
 * $Revision: 677240 $
 * $Date: 2008-07-16 04:25:47 -0700 (Wed, 16 Jul 2008) $
 *
 * ====================================================================
 * 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.impl.cookie;

import java.lang.ref.SoftReference;
import java.text.ParseException;
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;

/**
 * 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.
 * 
 * @author Christopher Brown
 * @author Michael Becke
 */
public final class DateUtils {

    /**
     * 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.
     */
    public static final String PATTERN_RFC1036 = "EEEE, dd-MMM-yy HH:mm:ss zzz";

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

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

    private static final Date DEFAULT_TWO_DIGIT_YEAR_START;
    
    public static final TimeZone GMT = TimeZone.getTimeZone("GMT");
    
    static {
        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.
     *
     * @param dateValue the date value to parse
     * 
     * @return the parsed date
     *
     * @throws DateParseException if the value could not be parsed using any of the 
     * supported date formats
     */
    public static Date parseDate(String dateValue) throws DateParseException {
        return parseDate(dateValue, null, null);
    }
    
    /**
     * 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
     * 
     * @throws DateParseException if none of the dataFormats could parse the dateValue
     */
    public static Date parseDate(final String dateValue, String[] dateFormats) 
        throws DateParseException {
        return parseDate(dateValue, dateFormats, null);
    }
    
    /**
     * 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</code> to <code>startDate + 100 years</code>. This value may 
     * be <code>null</code>. When <code>null</code> is given as a parameter, year 
     * <code>2000</code> will be used. 
     * 
     * @return the parsed date
     * 
     * @throws DateParseException if none of the dataFormats could parse the dateValue
     */
    public static Date parseDate(
        String dateValue, 
        String[] dateFormats,
        Date startDate 
    ) throws DateParseException {
        
        if (dateValue == null) {
            throw new IllegalArgumentException("dateValue is null");
        }
        if (dateFormats == null) {
            dateFormats = DEFAULT_PATTERNS;
        }
        if (startDate == null) {
            startDate = DEFAULT_TWO_DIGIT_YEAR_START;
        }
        // trim single quotes around date if present
        // see issue #5279
        if (dateValue.length() > 1 
            && dateValue.startsWith("'") 
            && dateValue.endsWith("'")
        ) {
            dateValue = dateValue.substring (1, dateValue.length() - 1);
        }

        for (String dateFormat : dateFormats) {
            SimpleDateFormat dateParser = DateFormatHolder.formatFor(dateFormat);
            dateParser.set2DigitYearStart(startDate);

            try {
                return dateParser.parse(dateValue);
            } catch (ParseException pe) {
                // ignore this exception, we will try the next format
            }
        }
        
        // we were unable to parse the date
        throw new DateParseException("Unable to parse the date " + dateValue);        
    }

    /**
     * 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(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 {@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(Date date, String pattern) {
        if (date == null) throw new IllegalArgumentException("date is null");
        if (pattern == null) throw new IllegalArgumentException("pattern is null");
        
        SimpleDateFormat formatter = DateFormatHolder.formatFor(pattern);
        return formatter.format(date);
    }
    
    /** This class should not be instantiated. */    
    private DateUtils() { 
    }
    
    /**
     * 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}.
     * 
     * @author Daniel Mueller
     */
    final static class DateFormatHolder {

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

            @Override
            protected SoftReference<Map<String, SimpleDateFormat>> initialValue() {
                return new SoftReference<Map<String, SimpleDateFormat>>(
                        new HashMap<String, SimpleDateFormat>());
            }
            
        };

        /**
         * creates a {@link SimpleDateFormat} for the requested format string.
         * 
         * @param pattern
         *            a non-<code>null</code> format String according to
         *            {@link SimpleDateFormat}. The format is not checked against
         *            <code>null</code> 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(String pattern) {
            SoftReference<Map<String, SimpleDateFormat>> ref = THREADLOCAL_FORMATS.get();
            Map<String, SimpleDateFormat> formats = 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;
        }
        
    }
    
}