Gazelle/sections/userhistory/thread_subscribe.php

<?
// perform the back end of subscribing to topics
authorize();

if (!empty($LoggedUser['DisableForums'])) {
	error(403);
}

if (!is_number($_GET['topicid'])) {
	error(0);
}

require(SERVER_ROOT.'/sections/forums/index.php');
$DB->query('SELECT ID FROM forums WHERE forums.ID = (SELECT ForumID FROM forums_topics WHERE ID = '.db_string($_GET['topicid']).')');
list($ForumID) = $DB->next_record();
if (!check_forumperm($ForumID)) {
	die();
}

if (!$UserSubscriptions = $Cache->get_value('subscriptions_user_'.$LoggedUser['ID'])) {
	$DB->query('SELECT TopicID FROM users_subscriptions WHERE UserID = '.db_string($LoggedUser['ID']));
	$UserSubscriptions = $DB->collect(0);
	$Cache->cache_value('subscriptions_user_'.$LoggedUser['ID'],$UserSubscriptions,0);
}

if (($Key = array_search($_GET['topicid'],$UserSubscriptions)) !== false) {
	$DB->query('DELETE FROM users_subscriptions WHERE UserID = '.db_string($LoggedUser['ID']).' AND TopicID = '.db_string($_GET['topicid']));
	unset($UserSubscriptions[$Key]);
} else {
	$DB->query("INSERT IGNORE INTO users_subscriptions (UserID, TopicID) VALUES ($LoggedUser[ID], ".db_string($_GET['topicid']).")");
	array_push($UserSubscriptions, $_GET['topicid']);
}
$Cache->replace_value('subscriptions_user_'.$LoggedUser['ID'], $UserSubscriptions, 0);
$Cache->delete_value('subscriptions_user_new_'.$LoggedUser['ID']);