This plugin records the IP address from bookings and allows you to block bookings by IP address or email address.

block-ips-for-rtb.php

<?php
/**
 * Plugin Name: Block Bookings by IP/Email Address for Restaurant Reservations
 * Plugin URI: http://themeofthecrop.com
 * Description: This plugin records the IP address from bookings and allows you to block bookings by IP address or email address.
 * Version: 0.1
 * Author: Theme of the Crop
 * Author URI: http://themeofthecrop.com
 * License:     GNU General Public License v2.0 or later
 * License URI: http://www.gnu.org/licenses/gpl-2.0.html
 *
 * This program is free software; you can redistribute it and/or modify it under the terms of the GNU
 * General Public License as published by the Free Software Foundation; either version 2 of the License,
 * or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
 * even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *
 * You should have received a copy of the GNU General Public License along with this program; if not, write
 * to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 */
defined( 'ABSPATH' ) || exit;

/**
 * Add options fields for entering banned IP addresses and email addresses
 *
 * @since 0.1
 */
function rtbbip_ban_options( $sap ) {

	$sap->add_setting(
		'rtb-settings',
		'rtb-general',
		'textarea',
		array(
			'id'			=> 'rtbbip-ban-ips',
			'title'			=> __( 'Banned IP Addresses', 'restaurant-reservations' ),
			'description'	=> __( 'You can block bookings from specific IP addresses. Enter each IP address on a separate line. Be aware that many internet providers rotate their IP address assignments, so an IP address may accidentally refer to a different user. Also, if you block an IP address used by a public connection, such as cafe WIFI, a public library, or a university network, you may inadvertantly block several people.', 'restaurant-reservations' ),
		)
	);

	$sap->add_setting(
		'rtb-settings',
		'rtb-general',
		'textarea',
		array(
			'id'			=> 'rtbbip-ban-emails',
			'title'			=> __( 'Banned Email Addresses', 'restaurant-reservations' ),
			'description'	=> __( 'You can block bookings from specific email addresses. Enter each email address on a separate line.', 'restaurant-reservations' ),
		)
	);

	return $sap;
}
add_filter( 'rtb_settings_page', 'rtbbip_ban_options' );

/**
 * Validate the IP and email address when submitted
 *
 * Bookings Managers bypass this validation. No IP address is stored if one is
 * already set to prevent overwriting the original IP when a booking is edited.
 *
 * @since 0.1
 */
function rtbbip_check_banned( $booking ) {

	if ( !current_user_can( 'manage_bookings' ) ) {

		$ip = $_SERVER['REMOTE_ADDR'];
		if ( !rtbbip_is_valid_ip( $ip ) || !rtbbip_is_valid_email( $booking->email ) ) {
			$booking->validation_errors[] = array(
				'field'			=> 'date',
				'post_variable'	=> $ip,
				'message'	=> __( 'Your booking has been rejected. Please call us if you would like to make a booking.', 'restaurant-reservations' ),
			);
		} elseif ( empty( $booking->rtbbip_ip ) ) {
			$booking->rtbbip_ip = $ip;
		}
	}
}
add_action( 'rtb_validate_booking_submission', 'rtbbip_check_banned' );

/**
 * Check if an IP has been blocked
 *
 * @since 0.1
 */
function rtbbip_is_valid_ip( $ip ) {

	global $rtb_controller;

	$banned_ips = array_filter( explode( "\n", $rtb_controller->settings->get_setting( 'rtbbip-ban-ips' ) ) );

	foreach( $banned_ips as $banned_ip ) {
		if ( $ip == trim( $banned_ip ) ) {
			return false;
		}
	}

	return true;
}

/**
 * Check if an email address has been blocked
 *
 * @since 0.1
 */
function rtbbip_is_valid_email( $email ) {

	global $rtb_controller;

	$banned_emails = array_filter( explode( "\n", $rtb_controller->settings->get_setting( 'rtbbip-ban-emails' ) ) );

	foreach( $banned_emails as $banned_email ) {
		if ( $email == trim( $banned_email ) ) {
			return false;
		}
	}

	return true;
}

/**
 * Save the IP address as metadata
 *
 * @since 0.1
 */
function rtbbip_save_ip( $meta, $booking ) {
	$meta['rtbbip_ip'] = isset( $booking->rtbbip_ip ) ? $booking->rtbbip_ip : '';
	return $meta;
}
add_filter( 'rtb_insert_booking_metadata', 'rtbbip_save_ip', 10, 2 );

/**
 * Load the IP address into the booking object
 *
 * @since 0.1
 */
function rtbbip_load_ip( $booking, $post ) {
	$meta = get_post_meta( $post->ID, 'rtb', true );
	if ( isset( $meta['rtbbip_ip'] ) ) {
		$booking->rtbbip_ip = $meta['rtbbip_ip'];
	}
}
add_filter( 'rtb_booking_load_post_data', 'rtbbip_load_ip', 10, 2 );

/**
 * Add a column to the bookings table for IP address
 *
 * @since 0.1
 */
function rtbbip_add_bookings_table_ip_column( $columns ) {
	$columns['rtbbip_ip'] = __( 'IP Address', 'restaurant-reservations' );
	return $columns;
}
add_filter( 'rtb_bookings_table_columns', 'rtbbip_add_bookings_table_ip_column' );