iCalender link integration for WordPress.

functions.php

<?php

/**
 *  iCalendar Feed
 */
class ICAL_Export
{
    // date format (WARNING: donnot change unless necessary)
    const DATE_FORMAT = 'Y-m-d';

    private static $feed_url_name = 'my-events';
    private static $location;
    private static $organizer;
    private static $date_start;
    private static $date_end;
    private static $time_start;
    private static $time_end;

    private static $date_start_format;
    private static $date_end_format;
    private static $time_start_format;
    private static $time_end_format;

    private static $reoccurrence_rule = FALSE;

    public static function load(array $parameters)
    {
        self::$location      = $parameters['location'];
        self::$organizer     = $parameters['organizer'];
        self::$date_start    = $parameters['date_start'];
        self::$date_end      = $parameters['date_end'];
        self::$time_start    = $parameters['time_start'];

        self::$date_start_format = $parameters['date_start_format'];
        self::$date_end_format   = $parameters['date_end_format'];
        self::$time_start_format = $parameters['time_start_format'];
        self::$time_end_format   = $parameters['time_end_format'];

        if (isset($parameters['feed_url_name']))
        {
            self::$feed_url_name = $parameters['feed_url_name'];
        }

        if (isset($parameters['reoccurrence_rule']))
        {
            self::$reoccurrence_rule = $parameters['reoccurrence_rule'];
        }

        add_feed(self::$feed_url_name, array(__CLASS__, 'export_calender'));
    }

    /**
     * Creates an ICAL file of events in the database
     */
    public function export_calender()
    {
        // retrieving the post id from the active url request
        $post_id = array_map('strrev', explode('&', strrev($_SERVER['QUERY_STRING'])));

        // Query for events (using the event page slug)
        $args = array
        (
            'p'         => (int) $post_id[0], // id of a page, post, or custom type
            'post_type' => 'any'
        );

        $my_post = new WP_Query($args);

        if ($my_post->have_posts())
        {
            // re-allocating post variables from parent object
            $my_post = $my_post->post;

            // Give the ICAL a filename
            $filename = self::str_to_url($my_post->post_title);

            // Collect output
            ob_start();

            // File header
            header('Content-Description: File Transfer');
            header('Content-Disposition: attachment; filename='.$filename);
            header('Content-type: text/calendar');
            header('Pragma: 0');
            header('Expires: 0');

            echo "BEGIN:VCALENDAR";
            echo "\nVERSION:2.0";
            echo "\nPRODID:-//".get_bloginfo('name')."//NONSGML Events //EN";
            echo "\nCALSCALE:GREGORIAN";
            echo "\nX-WR-CALNAME:".get_bloginfo('name')." - Events\n";

            $meta = get_post_meta($my_post->ID);

            echo "\nBEGIN:VEVENT";

            echo "\nSUMMARY:".trim(strip_tags($my_post->post_title));

            // Universal unique ID
            echo "\nUID:".htmlspecialchars_decode($my_post->guid);

            // date stamp for now
            echo "\nDTSTAMP:".date_i18n('Ymd\THis\Z', time(), TRUE);

            // time event created
            echo "\nCREATED:".get_post_time('Ymd\THis\Z', TRUE, $my_post->ID);

            // event start date
            if (self::$time_start == NULL)
            {
                echo "\nDTSTART;VALUE=DATE:".DateTime::createFromFormat(self::$date_start_format, $meta[self::$date_start][0])->format('Ymd');
            }
            else
            {
                echo "\nDTSTART:".DateTime::createFromFormat(self::$date_start_format.' '.self::$time_end_format, $meta[self::$date_start][0].' '.$meta[self::$time_start][0])->format('Ymd\THis\Z');
            }

            // event end date
            if (self::$time_end == NULL)
            {
                echo "\nDTEND;VALUE=DATE:".DateTime::createFromFormat(self::$date_end_format, $meta[self::$date_end][0])->format('Ymd');
            }
            else
            {
                echo "\nDTEND:".DateTime::createFromFormat(self::$date_end_format.' '.self::$time_end_format, $meta[self::$date_end][0].' '.$meta[self::$time_end][0])->format('Ymd\THis\Z');
            }

            // event reoccurrence rule
            if (self::$reoccurrence_rule)
            {
                echo "\nRRULE:".self::$reoccurrence_rule;
            }

            // event description (br and p replace with newline and removing all htmk)
            echo "\nDESCRIPTION:".substr(trim(preg_replace('#\s*\[.+\]\s*#U', ' ', str_replace('&nbsp;', '', strip_tags(str_replace(array('<br>', '<br/>', '<p>', '</p>'), "/n", trim($my_post->post_content)))))), 0, 255).'...';

            // event location
            echo "\nLOCATION:".str_replace(',', '\,', $meta[self::$location][0]).'\, Luxembourg';

            // event organiser
            echo "\nORGANIZER: ".ucwords(strtolower($meta[self::$organizer][0]));
            echo "\nEND:VEVENT\n";
        }

        echo "\nEND:VCALENDAR";

        // Collect output and echo
        $eventsical = ob_get_contents();
                      ob_end_clean();

        echo $eventsical;

        exit;
    }

    /**
     * Creates an ICAL file of events in the database
     *  @param string text - the string text to convert
     */
    private static function str_to_url($text)
    {
        return (string) strtolower(
            str_replace('--', '-',
                str_replace(array('+', ' '), '-',
                    htmlentities('Event-'.
                        str_replace(array('&', '+', '?', ',', '@', '!', '#', '$', '%', '^', '*', '=', '.'), '',
                            strip_tags(remove_accents($text))).'-'.date(self::DATE_FORMAT).'.ics'))));
    }
}

ICAL_Export::load(array
(
    'location'      => 'event_location',       // venue and/or address
    'organizer'     => 'event_organiser_name', // company or organizator
    'date_start'    => 'start_date',           // event start date
    'date_end'      => 'end_date',             // event end date
    'time_start'    => NULL,                   // event start time
    'time_end'      => NULL,                   // event end time
    'date_start_format' => 'Ymd',
    'date_end_format'   => 'Ymd',
    'time_start_format' => NULL,
    'time_end_format'   => NULL
));

Applied to the WP functions "functions.php" which is ideally located within your currently used 'theme' main folder. Then add <a href="<?php echo get_feed_link('my-events').'&'.get_the_ID(); ?>">LINK HERE</a> to any template HTML page where the iCal link is located.

If the above link link code doesn't work then try: <a href="/?feed=my-events&<?php echo get_the_ID();?>">LINK HERE</a>..

However, all in all, if you want full calendar functionality, I would consider and invest in looking to http://addtocalendar.com/