### FeedWriter.php

<?php

require_once 'FeedWriterItem.php';
require_once 'FeedWriterTitle.php';

abstract class FeedWriter {
    /**
     * Write feed. Needs subclass to work.
     *
     * @param Array of FeedWriter Item instances
     * @param FeedWriterTitle instance
     */
    public function main(&$arrItems, &$title) {
        // Send headers
        if (headers_sent() === false) {
            header("Last-Modified: " . date("D, M j Y G:i:s O", $title->lastUpdated));
            $this->sendHeader();
        }
  
        $this->printTitle($title);
  
        foreach($arrItems as $item) {
            $this->printItem($item);
        }
  
        $this->printEnd();
    }
  
    protected function sendHeader() {
        header("Content-Type: text/xml");
    }
  
    abstract protected function printItem($item);
  
    abstract protected function printTitle($title);
  
    abstract protected function printEnd();
}


### FeedWriterRssWriter.php 
<?php
require_once 'FeedWriter.php';

class FeedWriterRssWriter extends FeedWriter {  
    protected function sendHeader() {
        header("Content-Type: text/xml");
    }
  
    protected function printItem($item) {
        ?>
  <item>
    <title><?php print $item->title; ?></title>
    <link><?php print $item->link; ?></link>
    <description><?php print $item->description; ?></description>
    <content:encoded><?php print $item->content; ?></content:encoded>
    <pubDate><?php print date(DATE_RFC822, $item->pubDate); ?></pubDate>
    <guid isPermaLink="true"><?php print $item->guid; ?></guid>
    <author><?php print $item->author; ?></author>
  </item>
  <?php
    }
  
    protected function printTitle($title) {
        print '<?xml version="1.0" encoding="' . $title->encoding . '"?>';
  ?>
  <rss version="2.0"
    xmlns:content="http://purl.org/rss/1.0/modules/content/"
    xmlns:wfw="http://wellformedweb.org/CommentAPI/"
  >
  <channel>
    <title><?php print $title->title; ?></title>
    <link><?php print $title->link; ?></link>
    <description><?php print $title->description; ?></description>
    <language>de</language>
    <pubDate><?php print date(DATE_RFC822, $title->lastUpdated); ?></pubDate>
    <generator><?php print $title->generator; ?></generator>
    <image>
      <title><?php print $title->title; ?></title>
      <link><?php print $title->link; ?></link>
      <url><?php print $title->imageURL; ?></url>
    </image>
  <?php
    }
  
    protected function printEnd() {
  ?>
  </channel>
  </rss>
  <?php
    }
}

### FeedWriterItem.php 
<?php
  /**
* Simple Date Structure holding feed item data
*/
class FeedWriterItem {
  public $description = '';
  public $title = '';
  public $link = '';
  public $pubDate = ''; // this is a date, no string!
  public $guid = '';
  public $author = '';
  public $content = '';
}

### FeedWriterTitle.php 
<?php

  /**
 * Simple Date Structure holding feed data
 */
class FeedWriterTitle {
    public $title = '';
    public $lastUpdated = ''; // this is a date, no string!
    public $description = '';
    public $link = '';
    public $imageURL = '';
    public $generator = '';
    public $encoding = 'Utf-8';
}


#
# usage
#
<?php


error_reporting(E_ALL);

require_once 'FeedWriter/FeedWriterRssWriter.php';

define('NUMBEROFPOSTS', 6);
define('GENERATOR', 'Sommerzeit Benachrichtigung');


//get RSS get parm
if (isset($_GET['rss'])) {
    $rss = (boolean) $_GET['rss'];
    header('Content-type: application/rss+xml; charset=UTF-8');
}
else {
    $rss = false;
    header('Content-type: text/plain; charset=UTF-8');
}

//get date GET
if (isset($_GET['date'])) {
    $now = (int) $_GET['date'];
    $numberOfPosts = 1;
}
else {
    $now = gmmktime();
    $numberOfPosts = NUMBEROFPOSTS;
}

//get prepublish GET
if (isset($_GET['prepublish'])) {
    $prePublish = (int) $_GET['prepublish'];
    $prePublish *= 60 * 60 * 24;
}
else {
    $prePublish = 0;
}

$locales = array('de_DE@euro',
                 'de_DE',
                 'en_EN');
$timezones = array(-1,
                   -1,
                   0);
//get timezone GET
if (isset($_GET['locale']) && ($key = array_search($_GET['locale'], $locales)) !== false) {
    $locale = setlocale(LC_ALL, $locales[$key]);
    $timezone = $timezones[$key];
}
else {
    $locale = setlocale(LC_ALL, 'de_DE@euro', 'de_DE', 'de', 'ge');
    $timezone = -1;
}
//make timezone calculations
define('URL', 'http://userp.uni-koblenz.de/~hrehfeld/time/time.php?timezone=' . $timezone);

//calculate current time
$now += $prePublish;

$currentYear = gmdate('Y', $now);
$currentMonth = gmdate('m', $now);

//caculate if the last change was a MESZ -> normal time change
$back = (boolean) ($currentMonth - 3) / 6;

$items = array();
for ($i = 0; $i < $numberOfPosts; ++$i) {
    $year = (int) ($currentYear - ( $i / 2));
    
    $lastChangeTime = getMeszShiftTime($year, $back);

    if (!$back) {
        $season = 'vor auf Sommer';
    }
    else {
        $season = 'zurück auf Normal';
    }

    $description = 'Zeitumstellung '
        . $season . 'zeit am ' . readableDate($lastChangeTime, $timezone);

    if ($rss) {
        $item = new FeedWriterItem();
        $pubdate = $lastChangeTime - $prePublish;
        $item->pubDate = $pubdate;

        $item->description = $description;
        $item->title = $item->description;
        $item->content = $item->description;
        $item->guid = URL . '&amp;date=' . $lastChangeTime;
        $item->link = URL;


        $items[] = $item;
    }
    else {
        echo  $description, "\n";
    }
    
    $back = !$back;
}

if ($rss) {
    $title = new FeedWriterTitle();
    $title->generator = GENERATOR;
    $title->lastUpdated = getMeszShiftTime($currentYear, $back) - $timezone;
    $title->description = 'Sommer-/Normalzeitumstellungsbenachrichtigung';
    $title->title = $title->description;
    $title->link = URL;


    $writer = new FeedWriterRssWriter();
    $writer->main($items, $title);
}

function getMeszShiftTime($year, $back = false) {
    if ($back) {
        $month = 10;
    }
    else {
        $month = 3;
    }

    //find last sunday in month
    $lastDay = gmdate('w', gmmktime(0, 0, 0, $month, 31, $year, 0));
    $day = 31 - $lastDay;
    
    // in oct time changes at 3 oclock, not 2
    $hours = 1 + (int) $back;
    
    //return a timestamp
    return gmmktime($hours, 00, 0, $month, $day, $year);
}
    
    
function readableDate($time, $timezone = -1) {
    $time -= $timezone * 60 * 60;
    return mb_convert_encoding(strftime('%A, dem %e. %B %Y', $time), 'utf-8') . ' um ' . gmdate('G:i', $time);
}