WP Restrict Unwanted Users - restrict unwanted users from visiting the site (Link: https://wordpress.stackexchange.com/a/306082/22728)

wpse-restrict-unwanted-users.php

<?php
/**
 * Plugin Name: WPSE Restrict Unwanted Users
 * Plugin URI: 	https://wordpress.stackexchange.com/a/306082/22728
 * Description: Restrict unwanted users from visiting the site
 * Author: 	Mayeenul Islam
 * Version: 	1.0.0
 * License: 	GPL-2.0+
 * License URI: http://www.gnu.org/licenses/gpl-2.0.txt
 */

/**
 * Get the user's IP address
 * 
 * For the prohibition of multiple vote count on Star Rating, we are grabbing the
 * user's IP address and storing it to database for the time we want to restrict
 * the user into voting again.
 * 
 * @author Barış Ünver
 * @link   http://code.tutsplus.com/articles/creating-a-simple-contact-form-for-simple-needs--wp-27893
 * 
 * @return string IP address, formatted.
 * ------------------------------------------------------------------------------
 */
function wpse_306059_22728_get_the_ip() {
    if (isset($_SERVER["HTTP_X_FORWARDED_FOR"])) {
        return $_SERVER["HTTP_X_FORWARDED_FOR"];
    }
    elseif (isset($_SERVER["HTTP_CLIENT_IP"])) {
        return $_SERVER["HTTP_CLIENT_IP"];
    }
    else {
        return $_SERVER["REMOTE_ADDR"];
    }
}

/**
 * Restrict the user and display a message.
 *
 * @see wpse_306059_22728_get_the_ip()
 * @see wp_die()
 * 
 * @return void
 * ------------------------------------------------------------------------------
 */
function wpse_306059_22728_restrict_user() {
	// Get the list of blocked IP address in comma separated string.
	$black_list      = '0.0.0.0, 1.1.1.1, ::1'; // use get_option('your_spam_user_block_list')

	// make it an array
	$block_array     = explode(',', $black_list);
	$block_array     = array_map('trim', $block_array); // remove the spaces

	// get current user's IP address
	$current_user_ip = wpse_306059_22728_get_the_ip();

	// Restrict the user
	if( in_array($current_user_ip, $block_array) ) {
		$message = '<h3>'. __('Access Restricted', 'wpse-restrict-unwanted-users') .'</h3>';
		$message .= '<p>'. __( 'It seems the IP address you are using is spamming us. We are sorry for your inconvenience, but your access to the site is restricted.', 'wpse-restrict-unwanted-users' ) .'</p>';
		$message .= '<p>'. sprintf( __( 'If the message seems wrong to you, please contact us by emailing at: <strong>%s</strong>', 'wpse-restrict-unwanted-users' ), antispambot( 'yourname@example.com' ) ) .'</p>';

		wp_die(
			$message, // message
			__( 'Access Restricted', 'wpse-restrict-unwanted-users' ) // page title
		);
	}
}

add_action( 'wp', 'wpse_306059_22728_restrict_user' );