Expanding events manually based on alarm range

alarmexpand.php

<?php

function alarmExpand(Sabre_VObject_Component_VCalendar $calendar, DateTime $start, DateTime $end) {

    // You should adjust these to be more reasonable
    $startScan = new DateTime('1995-01-01');
    $endScan = new DateTime('2030-01-01');

    $newEvents = array();

    foreach($calendar->select('VEVENT') as $key=>$vevent) {

        if (isset($vevent->{'RECURRENCE-ID'})) {
            // Overridden event
            continue;
        } 


        if (!$vevent->rrule) {
            $newEvents[] = $vevent;
            continue;
        }

        $uid = (string)$vevent->uid;
        if (!$uid) {
            throw new LogicException('Event did not have a UID!');
        }

        $it = new Sabre_VObject_RecurrenceIterator($calendar, $vevent->uid);
        $it->fastForward($startScan);

        while($it->valid() && $it->getDTStart() < $endScan) {

            $newEvents[] = $it->getEventObject();
            $it->next();

        }
        unset($calendar->children[$key]);

    }

    // Removing all existing events
    unset($calendar->VEVENT);

    foreach($newEvents as $newEvent) {

        $inRange = false;
        foreach($newEvent->VALARM as $alarm) {
            if ($alarm->isInTimeRange($start, $end)) {
                $inRange = true;
                break;
            }
        }
        if (!$inRange) continue;

        // Note: If you don't care to normalize everything to UTC, you can skip this step.
        foreach($newEvent->children as $child) {
            if ($child instanceof Sabre_VObject_Property_DateTime &&
                $child->getDateType() == Sabre_VObject_Property_DateTime::LOCALTZ) {
                    $child->setDateTime($child->getDateTime(),Sabre_VObject_Property_DateTime::UTC);
                }
        }

        $calendar->add($newEvent);

    }

    // Removing all VTIMEZONE components
    unset($calendar->VTIMEZONE);

}