Create iCal Event For Shift: Designed to integrate with the Employee Scheduler plugin for Wordpress

createiCalShiftEvent.php

<?php
/*This will use the metadata from a shift page created using Employee Scheduler (Shiftee) and create an iCal link with event*/

// Add a custom endpoint "calendar"
function add_calendar_feed()
{
    
    add_feed('calendar', 'export_ics');
    // Only uncomment these 2 lines the first time you load this script, to update WP rewrite rules
    /*global $wp_rewrite;
    $wp_rewrite->flush_rules( false );*/
}
add_action('init', 'add_calendar_feed');
function export_ics()
{
    /*  For a better understanding of ics requirements and time formats
    please check https://gist.github.com/jakebellacera/635416   */
    // Query the event
    $the_event = new WP_Query(array(
        'post_type' => 'shift',
        'posts_per_page' => '1' //Limit to one to snag just this shift
    ));
    // Escapes a string of characters
    function escapeString($string)
    {
        return preg_replace('/([\,;])/', '\\\$1', $string);
    }
    // Cut it
    function shorter_version($string, $lenght)
    {
        if (strlen($string) >= $lenght) {
            return substr($string, 0, $lenght);
        } else {
            return $string;
        }
    }
    if ($the_event->have_posts()):
        while ($the_event->have_posts()):
            $the_event->the_post();
            /*  The correct date format, for ALL dates is date_i18n('Ymd\THis\Z',time(), true)
            So if your date is not in this format, use that function    */
            
            $startTime = get_post_meta(get_the_ID(), '_wpaesm_starttime', true);
            $endTime   = get_post_meta(get_the_ID(), '_wpaesm_endtime', true);
            $eventDate = get_post_meta(get_the_ID(), '_wpaesm_date', true);
            
            $startCombined = $eventDate . " " . $startTime . ":00";
            $endCombined   = $eventDate . " " . $endTime . ":00";
            
            /*Then convert the strings to date values*/
            $tempStart  = DateTime::createFromFormat('Y-m-d H:i:s', $startCombined);
            $eventStart = $tempStart->format('Ymd\THis\Z');
            
            $tempEnd  = DateTime::createFromFormat('Y-m-d H:i:s', $endCombined);
            $eventEnd = $tempEnd->format('Ymd\THis\Z');
            
            $timestamp    = date_i18n('Ymd\THis\Z', time(), true);
            $uid          = get_the_ID();
            $created_date = get_post_time('Ymd\THis\Z', true, $uid);
            $start_date   = $eventStart;
            $end_date     = $eventEnd;
            $deadline     = $eventEnd;
            $organiser    = get_bloginfo('name');
            $address      = '';
            $url          = get_the_permalink();
            $summary      = get_the_excerpt();
            $content      = trim(preg_replace('/\s\s+/', ' ', get_the_content())); // removes newlines and double spaces
            //Give the iCal export a filename
            $filename     = urlencode(get_the_title() . '-ical-' . date('Y-m-d') . '.ics');
            $eol          = "\r\n";
            //Collect output
            ob_start();
            // Set the correct headers for this file
            header("Content-Description: File Transfer");
            header("Content-Disposition: attachment; filename=" . $filename);
            header('Content-type: text/calendar; charset=utf-8');
            header("Pragma: 0");
            header("Expires: 0");
            // The below ics structure MUST NOT have spaces before each line
            // Credit for the .ics structure goes to https://gist.github.com/jakebellacera/635416
?>
BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//<?php
            echo get_bloginfo('name') . $eol;
?> //NONSGML Events //EN
CALSCALE:GREGORIAN
X-WR-CALNAME:<?php
            echo get_bloginfo('name') . $eol;
?>
BEGIN:VEVENT
CREATED:<?php
            echo $created_date . $eol;
?>
UID:<?php
            echo $uid . $eol;
?>
DTEND;VALUE=DATE:<?php
            echo $end_date . $eol;
?>
DTSTART;VALUE=DATE:<?php
            echo $start_date . $eol;
?>
DTSTAMP:<?php
            echo $timestamp . $eol;
?>
LOCATION:<?php
            echo escapeString($address) . $eol;
?>
DESCRIPTION:<?php
            echo shorter_version($content, 70) . $eol;
?>
SUMMARY:<?php
            echo escapeString(get_the_title()) . $eol;
?>
ORGANIZER:<?php
            echo escapeString($organiser) . $eol;
?>
URL;VALUE=URI:<?php
            echo escapeString($url) . $eol;
?>
TRANSP:OPAQUE
BEGIN:VALARM
ACTION:DISPLAY
TRIGGER;VALUE=DATE-TIME:<?php
            echo $deadline . $eol;
?>
DESCRIPTION:Reminder for <?php
            echo escapeString(get_the_title());
            echo $eol;
?>
END:VALARM
END:VEVENT
<?php
        endwhile;
?>
END:VCALENDAR
<?php
        //Collect output and echo
        $eventsical = ob_get_contents();
        ob_end_clean();
        echo $eventsical;
        exit();
    endif;
}
?>