Emergency Lockdown Switch

$wpide_locked = function () {
    return '1' === get_option( 'wpide_lockdown' );
};

add_action( 'admin_bar_menu', function ( $bar ) use ( $wpide_locked ) {
    if ( ! current_user_can( 'manage_options' ) ) {
        return;
    }

    $bar->add_node( array(
        'id'    => 'wpide-lockdown',
        'title' => $wpide_locked() ? 'Lockdown: ON' : 'Lockdown: off',
        'href'  => wp_nonce_url( admin_url( 'admin-post.php?action=wpide_lockdown' ), 'wpide_lockdown' ),
        'meta'  => array( 'title' => 'Toggle emergency lockdown' ),
    ) );
}, 999 );

add_action( 'admin_post_wpide_lockdown', function () use ( $wpide_locked ) {
    if ( ! current_user_can( 'manage_options' ) ) {
        wp_die( esc_html__( 'Sorry, you are not allowed to do that.' ), 403 );
    }

    check_admin_referer( 'wpide_lockdown' );
    update_option( 'wpide_lockdown', $wpide_locked() ? '0' : '1' );
    wp_safe_redirect( wp_get_referer() ? wp_get_referer() : admin_url() );
    exit;
} );

add_action( 'init', function () use ( $wpide_locked ) {
    if ( ! $wpide_locked() ) {
        return;
    }

    add_filter( 'pre_option_users_can_register', '__return_zero' );
    add_filter( 'comments_open', '__return_false', 99 );
    add_filter( 'xmlrpc_enabled', '__return_false' );
    add_filter( 'xmlrpc_methods', '__return_empty_array' );
    add_filter( 'authenticate', function ( $user ) {
        return ( $user instanceof WP_User && ! user_can( $user, 'manage_options' ) ) ? new WP_Error( 'wpide_lockdown', 'Logins are temporarily disabled.' ) : $user;
    }, 99 );

    if ( is_user_logged_in() && ! current_user_can( 'manage_options' ) ) {
        wp_logout();
    }
}, 1 );