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/* HTTPDateFormat.java --

   Copyright (C) 2004 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 2, or (at your option)

any later version.

GNU Classpath is distributed in the hope that it will be useful, but

WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

General Public License for more details.

You should have received a copy of the GNU General Public License

along with GNU Classpath; see the file COPYING.  If not, write to the

Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301 USA.

Linking this library statically or dynamically with other modules is

making a combined work based on this library.  Thus, the terms and

conditions of the GNU General Public License cover the whole

combination.

As a special exception, the copyright holders of this library give you

permission to link this library with independent modules to produce an

executable, regardless of the license terms of these independent

modules, and to copy and distribute the resulting executable under

terms of your choice, provided that you also meet, for each linked

independent module, the terms and conditions of the license of that

module.  An independent module is a module which is not derived from

or based on this library.  If you modify this library, you may extend

this exception to your version of the library, but you are not

obligated to do so.  If you do not wish to do so, delete this

exception statement from your version. */

package gnu.java.net.protocol.http;

import java.text.DateFormat;

import java.text.DecimalFormat;

import java.text.FieldPosition;

import java.text.NumberFormat;

import java.text.ParsePosition;

import java.util.Calendar;

import java.util.Date;

import java.util.GregorianCalendar;

import java.util.TimeZone;

/**

 * HTTP date formatter and parser.

 * Formats dates according to RFC 822 (updated by RFC 1123).

 * Parses dates according to the above, <i>or</i> RFC 1036, <i>or</i> the

 * ANSI C <code>asctime()</code> format.

 *

 * @author Chris Burdess (dog@gnu.org)

 */

public class HTTPDateFormat

  extends DateFormat

{

  static final String[] DAYS_OF_WEEK = {

    null, "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"

  };

  static final String[] MONTHS = {

    "Jan", "Feb", "Mar", "Apr", "May", "Jun",

    "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"

  };

  public HTTPDateFormat()

  {

    calendar = new GregorianCalendar(TimeZone.getTimeZone ("GMT"));

    numberFormat = new DecimalFormat();

  }

  /**

   * Appends the textual value for the specified field to the given string

   * buffer. This method should be avoided, use <code>format(Date)</code>

   * instead.

   * @param date the Date object

   * @param buf the buffer to append to

   * @param field the current field position

   * @return the modified buffer

   */

  public StringBuffer format(Date date, StringBuffer buf,

                             FieldPosition field)

  {

    calendar.clear();

    calendar.setTime(date);

    buf.setLength(0);

    // Day of week

    buf.append(DAYS_OF_WEEK[calendar.get(Calendar.DAY_OF_WEEK)]);

    buf.append(',');

    buf.append(' ');

    // Day of month

    int day = calendar.get(Calendar.DAY_OF_MONTH);

    buf.append(Character.forDigit(day / 10, 10));

    buf.append(Character.forDigit(day % 10, 10));

    buf.append(' ');

    // Month

    buf.append(MONTHS[calendar.get(Calendar.MONTH)]);

    buf.append(' ');

    // Year

    int year = calendar.get(Calendar.YEAR);

    if (year < 1000)

      {

        buf.append('0');

        if (year < 100)

          {

            buf.append('0');

            if (year < 10)

              {

                buf.append('0');

              }

          }

      }

    buf.append(Integer.toString(year));

    buf.append(' ');

    // Hour

    int hour = calendar.get(Calendar.HOUR_OF_DAY);

    buf.append(Character.forDigit(hour / 10, 10));

    buf.append(Character.forDigit(hour % 10, 10));

    buf.append(':');

    // Minute

    int minute = calendar.get(Calendar.MINUTE);

    buf.append(Character.forDigit(minute / 10, 10));

    buf.append(Character.forDigit(minute % 10, 10));

    buf.append(':');

    // Second

    int second = calendar.get(Calendar.SECOND);

    buf.append(Character.forDigit(second / 10, 10));

    buf.append(Character.forDigit(second % 10, 10));

    buf.append(' ');

    // Timezone

    // Get time offset in minutes

    int zoneOffset =(calendar.get(Calendar.ZONE_OFFSET) +

                     calendar.get(Calendar.DST_OFFSET)) / 60000;

    // Apply + or - appropriately

    if (zoneOffset < 0)

      {

        zoneOffset = -zoneOffset;

        buf.append('-');

      }

    else

      {

        buf.append('+');

      }

    // Set the 2 2-char fields as specified above

    int tzhours = zoneOffset / 60;

    buf.append(Character.forDigit(tzhours / 10, 10));

    buf.append(Character.forDigit(tzhours % 10, 10));

    int tzminutes = zoneOffset % 60;

    buf.append(Character.forDigit(tzminutes / 10, 10));

    buf.append(Character.forDigit(tzminutes % 10, 10));

    field.setBeginIndex(0);

    field.setEndIndex(buf.length());

    return buf;

  }

  /**

   * Parses the given date in the current TimeZone.

   * @param text the formatted date to be parsed

   * @param pos the current parse position

   */

  public Date parse(String text, ParsePosition pos)

  {

    int date, month, year, hour, minute, second;

    String monthText;

    int start = 0, end = -1;

    int len = text.length();

    calendar.clear();

    pos.setIndex(start);

    try

      {

        // Advance to date

        if (Character.isLetter(text.charAt(start)))

          {

            start = skipNonWhitespace(text, start);

          }

        // Determine mode

        switch(start)

          {

          case 3:

            // asctime

            start = skipWhitespace(text, start);

            pos.setIndex(start);

            end = skipNonWhitespace(text, start + 1);

            monthText = text.substring(start, end);

            month = -1;

            for (int i = 0; i < 12; i++)

              {

                if (MONTHS[i].equals(monthText))

                  {

                    month = i;

                    break;

                  }

              }

            if (month == -1)

              {

                pos.setErrorIndex(end);

                return null;

              }

            // Advance to date

            start = skipWhitespace(text, end + 1);

            pos.setIndex(start);

            end = skipNonWhitespace(text, start + 1);

            date = Integer.parseInt(text.substring(start, end));

            // Advance to hour

            start = skipWhitespace(text, end + 1);

            pos.setIndex(start);

            end = skipTo(text, start + 1, ':');

            hour = Integer.parseInt(text.substring(start, end));

            // Advance to minute

            start = end + 1;

            pos.setIndex(start);

            end = skipTo(text, start + 1, ':');

            minute = Integer.parseInt(text.substring(start, end));

            // Advance to second

            start = end + 1;

            pos.setIndex(start);

            end = skipNonWhitespace(text, start + 1);

            second = Integer.parseInt(text.substring(start, end));

            // Advance to year

            start = skipWhitespace(text, end + 1);

            pos.setIndex(start);

            end = skipNonWhitespace(text, start + 1);

            year = Integer.parseInt(text.substring(start, end));

            break;

          case 0:

          case 4:

            // rfc822

            start = skipWhitespace(text, start);

            pos.setIndex(start);

            end = skipNonWhitespace(text, start + 1);

            date = Integer.parseInt(text.substring(start, end));

            // Advance to month

            start = skipWhitespace(text, end + 1);

            pos.setIndex(start);

            end = skipNonWhitespace(text, start + 1);

            monthText = text.substring(start, end);

            month = -1;

            for (int i = 0; i < 12; i++)

              {

                if (MONTHS[i].equals(monthText))

                  {

                    month = i;

                    break;

                  }

              }

            if (month == -1)

              {

                pos.setErrorIndex(end);

                return null;

              }

            // Advance to year

            start = skipWhitespace(text, end + 1);

            pos.setIndex(start);

            end = skipNonWhitespace(text, start + 1);

            year = Integer.parseInt(text.substring(start, end));

            // Advance to hour

            start = skipWhitespace(text, end + 1);

            pos.setIndex(start);

            end = skipTo(text, start + 1, ':');

            hour = Integer.parseInt(text.substring(start, end));

            // Advance to minute

            start = end + 1;

            pos.setIndex(start);

            end = skipTo(text, start + 1, ':');

            minute = Integer.parseInt(text.substring(start, end));

            // Advance to second

            start = end + 1;

            pos.setIndex(start);

            end = start + 1;

            while (end < len && !Character.isWhitespace(text.charAt(end)))

              {

                end++;

              }

            second = Integer.parseInt(text.substring(start, end));

            break;

          default:

            // rfc850(obsolete)

            start = skipWhitespace(text, start);

            pos.setIndex(start);

            end = skipTo(text, start + 1, '-');

            date = Integer.parseInt(text.substring(start, end));

            // Advance to month

            start = end + 1;

            pos.setIndex(start);

            end = skipTo(text, start + 1, '-');

            monthText = text.substring(start, end);

            month = -1;

            for (int i = 0; i < 12; i++)

              {

                if (MONTHS[i].equals(monthText))

                  {

                    month = i;

                    break;

                  }

              }

            if (month == -1)

              {

                pos.setErrorIndex(end);

                return null;

              }

            // Advance to year

            start = end + 1;

            pos.setIndex(start);

            end = skipNonWhitespace(text, start + 1);

            year = 1900 + Integer.parseInt(text.substring(start, end));

            // Advance to hour

            start = skipWhitespace(text, end + 1);

            pos.setIndex(start);

            end = skipTo(text, start + 1, ':');

            hour = Integer.parseInt(text.substring(start, end));

            // Advance to minute

            start = end + 1;

            pos.setIndex(start);

            end = skipTo(text, start + 1, ':');

            minute = Integer.parseInt(text.substring(start, end));

            // Advance to second

            start = end + 1;

            pos.setIndex(start);

            end = start + 1;

            while (end < len && !Character.isWhitespace(text.charAt(end)))

              {

                end++;

              }

            second = Integer.parseInt(text.substring(start, end));

          }

        calendar.set(Calendar.YEAR, year);

        calendar.set(Calendar.MONTH, month);

        calendar.set(Calendar.DAY_OF_MONTH, date);

        calendar.set(Calendar.HOUR, hour);

        calendar.set(Calendar.MINUTE, minute);

        calendar.set(Calendar.SECOND, second);

        if (end != len)

          {

            // Timezone

            start = skipWhitespace(text, end + 1);

            end = start + 1;

            while (end < len && !Character.isWhitespace(text.charAt(end)))

              {

                end++;

              }

            char pm = text.charAt(start);

            if (Character.isLetter(pm))

              {

                TimeZone tz =

                  TimeZone.getTimeZone(text.substring(start, end));

                calendar.set(Calendar.ZONE_OFFSET, tz.getRawOffset());

              }

            else

              {

                int zoneOffset = 0;

                zoneOffset += 600 * Character.digit(text.charAt(++start), 10);

                zoneOffset += 60 * Character.digit(text.charAt(++start), 10);

                zoneOffset += 10 * Character.digit(text.charAt(++start), 10);

                zoneOffset += Character.digit(text.charAt(++start), 10);

                zoneOffset *= 60000; // minutes -> ms

                if ('-' == pm)

                  {

                    zoneOffset = -zoneOffset;

                  }

                calendar.set(Calendar.ZONE_OFFSET, zoneOffset);

              }

          }

        pos.setIndex(end);

        return calendar.getTime();

      }

    catch (NumberFormatException e)

      {

        pos.setErrorIndex(Math.max(start, end));

      }

    catch (StringIndexOutOfBoundsException e)

      {

        pos.setErrorIndex(Math.max(start, end));

      }

    return null;

  }

  private int skipWhitespace(String text, int pos)

  {

    while(Character.isWhitespace(text.charAt(pos)))

      {

        pos++;

      }

    return pos;

  }

  private int skipNonWhitespace(String text, int pos)

  {

    while(!Character.isWhitespace(text.charAt(pos)))

      {

        pos++;

      }

    return pos;

  }

  private int skipTo(String text, int pos, char c)

  {

    while(text.charAt(pos) != c)

      {

        pos++;

      }

    return pos;

  }

  /**

   * Don't allow setting the calendar.

   */

  public void setCalendar(Calendar newCalendar)

  {

    throw new UnsupportedOperationException();

  }

  /**

   * Don't allow setting the NumberFormat.

   */

  public void setNumberFormat(NumberFormat newNumberFormat)

  {

    throw new UnsupportedOperationException();

  }

}