<?php

  namespace Sabre\HTTP;

  /**
   * HTTP utility methods
   *

   * @copyright Copyright (C) 2007-2014 fruux GmbH (https://fruux.com/).
   * @author Evert Pot (http://evertpot.com/)

   * @author Paul Voegler

   * @license http://sabre.io/license/ Modified BSD License

   */

  class Util {

  
      /**
       * Parses a RFC2616-compatible date string
       *
       * This method returns false if the date is invalid
       *
       * @param string $dateHeader
       * @return bool|DateTime
       */
      static function parseHTTPDate($dateHeader) {
  
          //RFC 2616 section 3.3.1 Full Date
          //Only the format is checked, valid ranges are checked by strtotime below
          $month = '(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)';
          $weekday = '(Monday|Tuesday|Wednesday|Thursday|Friday|Saturday|Sunday)';
          $wkday = '(Mon|Tue|Wed|Thu|Fri|Sat|Sun)';
          $time = '[0-2]\d(\:[0-5]\d){2}';
          $date3 = $month . ' ([1-3]\d| \d)';
          $date2 = '[0-3]\d\-' . $month . '\-\d\d';
          //4-digit year cannot begin with 0 - unix timestamp begins in 1970
          $date1 = '[0-3]\d ' . $month . ' [1-9]\d{3}';
  
          //ANSI C's asctime() format
          //4-digit year cannot begin with 0 - unix timestamp begins in 1970
          $asctime_date = $wkday . ' ' . $date3 . ' ' . $time . ' [1-9]\d{3}';
          //RFC 850, obsoleted by RFC 1036
          $rfc850_date = $weekday . ', ' . $date2 . ' ' . $time . ' GMT';
          //RFC 822, updated by RFC 1123
          $rfc1123_date = $wkday . ', ' . $date1 . ' ' . $time . ' GMT';
          //allowed date formats by RFC 2616
          $HTTP_date = "($rfc1123_date|$rfc850_date|$asctime_date)";
  
          //allow for space around the string and strip it
          $dateHeader = trim($dateHeader, ' ');
          if (!preg_match('/^' . $HTTP_date . '$/', $dateHeader))
              return false;
  
          //append implicit GMT timezone to ANSI C time format
          if (strpos($dateHeader, ' GMT') === false)
              $dateHeader .= ' GMT';
  
  
          $realDate = strtotime($dateHeader);
          //strtotime can return -1 or false in case of error
          if ($realDate !== false && $realDate >= 0)

              return new \DateTime('@' . $realDate, new \DateTimeZone('UTC'));

  
      }
  
      /**
       * Transforms a DateTime object to HTTP's most common date format.
       *
       * We're serializing it as the RFC 1123 date, which, for HTTP must be
       * specified as GMT.
       *

       * @param \DateTime $dateTime

       * @return string
       */

      static function toHTTPDate(\DateTime $dateTime) {

  
          // We need to clone it, as we don't want to affect the existing
          // DateTime.
          $dateTime = clone $dateTime;

          $dateTime->setTimeZone(new \DateTimeZone('GMT'));

          return $dateTime->format('D, d M Y H:i:s \G\M\T');
  
      }
  
  }