Sabre\VObject\ITip\Broker::processMessageReply PHP Method

    protected function processMessageReply(Message $itipMessage, VCalendar $existingObject = null)
    {
        // A reply can only be processed based on an existing object.
        // If the object is not available, the reply is ignored.
        if (!$existingObject) {
            return null;
        }
        $instances = array();
        $requestStatus = '2.0';
        // Finding all the instances the attendee replied to.
        foreach ($itipMessage->message->VEVENT as $vevent) {
            $recurId = isset($vevent->{'RECURRENCE-ID'}) ? $vevent->{'RECURRENCE-ID'}->getValue() : 'master';
            $attendee = $vevent->ATTENDEE;
            $instances[$recurId] = $attendee['PARTSTAT']->getValue();
            if (isset($vevent->{'REQUEST-STATUS'})) {
                $requestStatus = $vevent->{'REQUEST-STATUS'}->getValue();
                list($requestStatus) = explode(';', $requestStatus);
            }
        }
        // Now we need to loop through the original organizer event, to find
        // all the instances where we have a reply for.
        $masterObject = null;
        foreach ($existingObject->VEVENT as $vevent) {
            $recurId = isset($vevent->{'RECURRENCE-ID'}) ? $vevent->{'RECURRENCE-ID'}->getValue() : 'master';
            if ($recurId === 'master') {
                $masterObject = $vevent;
            }
            if (isset($instances[$recurId])) {
                $attendeeFound = false;
                if (isset($vevent->ATTENDEE)) {
                    foreach ($vevent->ATTENDEE as $attendee) {
                        if ($attendee->getValue() === $itipMessage->sender) {
                            $attendeeFound = true;
                            $attendee['PARTSTAT'] = $instances[$recurId];
                            $attendee['SCHEDULE-STATUS'] = $requestStatus;
                            // Un-setting the RSVP status, because we now know
                            // that the attende already replied.
                            unset($attendee['RSVP']);
                            break;
                        }
                    }
                }
                if (!$attendeeFound) {
                    // Adding a new attendee. The iTip documentation calls this
                    // a party crasher.
                    $attendee = $vevent->add('ATTENDEE', $itipMessage->sender, array('PARTSTAT' => $instances[$recurId]));
                    if ($itipMessage->senderName) {
                        $attendee['CN'] = $itipMessage->senderName;
                    }
                }
                unset($instances[$recurId]);
            }
        }
        if (!$masterObject) {
            // No master object, we can't add new instances.
            return null;
        }
        // If we got replies to instances that did not exist in the
        // original list, it means that new exceptions must be created.
        foreach ($instances as $recurId => $partstat) {
            $recurrenceIterator = new EventIterator($existingObject, $itipMessage->uid);
            $found = false;
            $iterations = 1000;
            do {
                $newObject = $recurrenceIterator->getEventObject();
                $recurrenceIterator->next();
                if (isset($newObject->{'RECURRENCE-ID'}) && $newObject->{'RECURRENCE-ID'}->getValue() === $recurId) {
                    $found = true;
                }
                $iterations--;
            } while ($recurrenceIterator->valid() && !$found && $iterations);
            // Invalid recurrence id. Skipping this object.
            if (!$found) {
                continue;
            }
            unset($newObject->RRULE, $newObject->EXDATE, $newObject->RDATE);
            $attendeeFound = false;
            if (isset($newObject->ATTENDEE)) {
                foreach ($newObject->ATTENDEE as $attendee) {
                    if ($attendee->getValue() === $itipMessage->sender) {
                        $attendeeFound = true;
                        $attendee['PARTSTAT'] = $partstat;
                        break;
                    }
                }
            }
            if (!$attendeeFound) {
                // Adding a new attendee
                $attendee = $newObject->add('ATTENDEE', $itipMessage->sender, array('PARTSTAT' => $partstat));
                if ($itipMessage->senderName) {
                    $attendee['CN'] = $itipMessage->senderName;
                }
            }
            $existingObject->add($newObject);
        }
        return $existingObject;
    }