/*
 * $Header: /home/cvs/jakarta-commons/httpclient/src/java/org/apache/commons/httpclient/util/DateParser.java,v 1.3.2.2 2004/02/22 18:21:16 olegk Exp $
 * $Revision: 1.3.2.2 $
 * $Date: 2004/02/22 18:21:16 $
 *
 * ====================================================================
 *
 *  Copyright 1999-2004 The Apache Software Foundation
 *
 *  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.
 * ====================================================================
 *
 * 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
 * .
 *
 * [Additional notices, if required by prior licensing conditions]
 *
 */

package org.apache.commons.httpclient.util;

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

/**
 * A utility class for parsing 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 class DateParser {

    /**
     * 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 
     * asctime() format.
     */
    public static final String PATTERN_ASCTIME = "EEE MMM d HH:mm:ss yyyy";

    /** The patterns used for parsing dates */
    private static final String[] DATE_PATTERNS = {
        PATTERN_RFC1123,
        PATTERN_RFC1036,
        PATTERN_ASCTIME,
        "EEE, dd-MMM-yyyy HH:mm:ss z",
        "EEE, dd-MMM-yyyy HH-mm-ss z",
        "EEE, dd MMM yy HH:mm:ss z",
        "EEE dd-MMM-yyyy HH:mm:ss z",
        "EEE dd MMM yyyy HH:mm:ss z",
        "EEE dd-MMM-yyyy HH-mm-ss z",
        "EEE dd-MMM-yy HH:mm:ss z",
        "EEE dd MMM yy HH:mm:ss z",
        "EEE,dd-MMM-yy HH:mm:ss z",
        "EEE,dd-MMM-yyyy HH:mm:ss z",
        "EEE, dd-MM-yyyy HH:mm:ss z",
    };

    /**
     * Parses a date value.
     *
     * @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, DATE_PATTERNS);
    }
    
    /**
     * Parses the date value using the array of 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
     */
    private static Date parseDate(
        String dateValue, 
        String[] dateFormats
    ) throws DateParseException {
        
        if (dateValue == null) {
            throw new IllegalArgumentException("dateValue is null");
        }
        
        SimpleDateFormat dateParser = null;
        
        for (int i = 0; i < dateFormats.length; i++) {
            if (dateParser == null) {
                dateParser = new SimpleDateFormat(dateFormats[i], Locale.US);
                dateParser.setTimeZone(TimeZone.getTimeZone("GMT"));
            } else {
                dateParser.applyPattern(dateFormats[i]);                    
            }
            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);        
    }

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