bbp_privatize_forum( int $forum_id,  $current_visibility = '' )

function bbp_privatize_forum( $forum_id = 0, $current_visibility = '' ) {

	$forum_id = bbp_get_forum_id( $forum_id );

	do_action( 'bbp_privatize_forum',  $forum_id );

	// Only run queries if visibility is changing
	if ( bbp_get_private_status_id() !== $current_visibility ) {

		// Get hidden forums
		$hidden = bbp_get_hidden_forum_ids();

		// Find this forum in the array
		if ( in_array( $forum_id, $hidden ) ) {

			$offset = array_search( $forum_id, $hidden );

			// Splice around it
			array_splice( $hidden, $offset, 1 );

			// Update hidden forums minus this one
			update_option( '_bbp_hidden_forums', array_unique( array_filter( array_values( $hidden ) ) ) );
		}

		// Add to '_bbp_private_forums' site option
		$private   = bbp_get_private_forum_ids();
		$private[] = $forum_id;
		update_option( '_bbp_private_forums', array_unique( array_filter( array_values( $private ) ) ) );

		// Update forums visibility setting
		global $wpdb;
		$wpdb->update( $wpdb->posts, array( 'post_status' => bbp_get_private_status_id() ), array( 'ID' => $forum_id ) );
		wp_transition_post_status( bbp_get_private_status_id(), $current_visibility, get_post( $forum_id ) );
		bbp_clean_post_cache( $forum_id );
	}

	do_action( 'bbp_privatized_forum', $forum_id );

	return $forum_id;
}