bbp_update_forum_last_active_id( int $forum_id, int $active_id )

function bbp_update_forum_last_active_id( $forum_id = 0, $active_id = 0 ) {

	$forum_id = bbp_get_forum_id( $forum_id );

	// Define local variable(s)
	$children_last_active = 0;

	// Do some calculation if not manually set
	if ( empty( $active_id ) ) {

		// Loop through children and add together forum reply counts
		$children = bbp_forum_query_subforum_ids( $forum_id );
		if ( !empty( $children ) ) {
			foreach ( (array) $children as $child ) {
				$children_last_active = bbp_update_forum_last_active_id( $child, $active_id );
			}
		}

		// Don't count replies if the forum is a category
		$topic_ids = bbp_forum_query_topic_ids( $forum_id );
		if ( !empty( $topic_ids ) ) {
			$active_id = bbp_forum_query_last_reply_id( $forum_id, $topic_ids );
			$active_id = $active_id > max( $topic_ids ) ? $active_id : max( $topic_ids );

		// Forum has no topics
		} else {
			$active_id = 0;
		}
	}

	// Cast as integer in case of empty or string
	$active_id            = (int) $active_id;
	$children_last_active = (int) $children_last_active;

	// If child forums have higher id, use that instead
	if ( !empty( $children ) && ( $children_last_active > $active_id ) )
		$active_id = $children_last_active;

	// Update only if published
	if ( bbp_get_public_status_id() === get_post_status( $active_id ) )
		update_post_meta( $forum_id, '_bbp_last_active_id', (int) $active_id );

	return (int) apply_filters( 'bbp_update_forum_last_active_id', (int) $active_id, $forum_id );
}