function HTFV_Change($topic = 0, $hide_topic = false)
{
	global $user_info, $smcFunc;

	// Abort if we are not supposed to be here!
	if (empty($user_info['id']) || empty($topic))
		fatal_lang_error('no_topic_id', false);
	
	// Get the board number that this topic resides in:
	$request = $smcFunc['db_query']('', '
		SELECT id_board
		FROM {db_prefix}topics
		WHERE id_topic IN ({int:id_topic})',
		array(
			'id_topic' => $topic = (int) $topic,
		)
	);
	list($board) = $smcFunc['db_fetch_row']($request);
	$smcFunc['db_free_result']($request);

	// Remove any existing entries for this topic:
	$smcFunc['db_query']('', '
		DELETE FROM {db_prefix}hide_topics
		WHERE id_member = {int:id_member}
			AND id_topic = {int:id_topic}',
		array(
			'id_member' => (int) $user_info['id'],
			'id_topic' => (int) $topic,
		)
	);

	// Are we being requested to hide the specified topic?
	if ($hide_topic)
	{
		// Can't do anything if the board ID is empty, either....
		$user = (int) $user_info['id'];
		if (empty($board))
			continue;

		// Insert the row into the hide_topics table:
		$smcFunc['db_insert']('insert',
			'{db_prefix}hide_topics',
			array('id_member' => 'int', 'id_topic' => 'int', 'id_board' => 'int'),
			array($user, $topic, (int) $board),
			array('id_member', 'id_topic', 'id_board')
		);
	}

	// Force recache of the hidden topics for this user, then go to the board:
	unset($_SESSION['hide_topics']);
	return $board;
}