ActivityModel::queueNotification PHP Method

    public function queueNotification($ActivityID, $Story = '', $Position = 'last', $Force = false)
    {
        $Activity = $this->getID($ActivityID);
        if (!is_object($Activity)) {
            return;
        }
        $Story = Gdn_Format::text($Story == '' ? $Activity->Story : $Story, false);
        // If this is a comment on another activity, fudge the activity a bit so that everything appears properly.
        if (is_null($Activity->RegardingUserID) && $Activity->CommentActivityID > 0) {
            $CommentActivity = $this->getID($Activity->CommentActivityID);
            $Activity->RegardingUserID = $CommentActivity->RegardingUserID;
            $Activity->Route = '/activity/item/' . $Activity->CommentActivityID;
        }
        $User = Gdn::userModel()->getID($Activity->RegardingUserID, DATASET_TYPE_OBJECT);
        if ($User) {
            if ($Force) {
                $Preference = $Force;
            } else {
                $ConfigPreference = c('Preferences.Email.' . $Activity->ActivityType, '0');
                if ($ConfigPreference !== false) {
                    $Preference = val('Email.' . $Activity->ActivityType, $User->Preferences, $ConfigPreference);
                } else {
                    $Preference = false;
                }
            }
            if ($Preference) {
                $ActivityHeadline = Gdn_Format::text(Gdn_Format::activityHeadline($Activity, $Activity->ActivityUserID, $Activity->RegardingUserID), false);
                $Email = new Gdn_Email();
                $Email->subject(sprintf(t('[%1$s] %2$s'), Gdn::config('Garden.Title'), $ActivityHeadline));
                $Email->to($User);
                $url = externalUrl(val('Route', $Activity) == '' ? '/' : val('Route', $Activity));
                $emailTemplate = $Email->getEmailTemplate()->setButton($url, val('ActionText', $Activity, t('Check it out')))->setTitle(Gdn_Format::plainText(val('Headline', $Activity)));
                if ($message = $this->getEmailMessage($Activity)) {
                    $emailTemplate->setMessage($message, true);
                }
                $Email->setEmailTemplate($emailTemplate);
                if (!array_key_exists($User->UserID, $this->_NotificationQueue)) {
                    $this->_NotificationQueue[$User->UserID] = [];
                }
                $Notification = ['ActivityID' => $ActivityID, 'User' => $User, 'Email' => $Email, 'Route' => $Activity->Route, 'Story' => $Story, 'Headline' => $ActivityHeadline, 'Activity' => $Activity];
                if ($Position == 'first') {
                    $this->_NotificationQueue[$User->UserID] = array_merge([$Notification], $this->_NotificationQueue[$User->UserID]);
                } else {
                    $this->_NotificationQueue[$User->UserID][] = $Notification;
                }
            }
        }
    }