Functions for a Genesis child theme's splash page asking the visitor to certify he/she is over 21.

age-check-genesis-theme.php

<?php 
/**
 * Set & read cookie for age-check in a Genesis child theme. On first visit to the site (any page) 
 * visitors are redirected to the page /age-check/. The age check page uses a custom page template 
 * containing part of the code here. The first two functions "set_newuser_cookie()" 
 * and "cur_page_url()" should go in your functions file. 
 * The code below that is for your custom page template.
 *
 * @author Pat Ramsey
 *
 */

/*
 * This goes in your functions file
 */

add_action( 'genesis_pre', 'set_newuser_cookie');
function set_newuser_cookie() {
	if ( !is_admin() ) {
		if (isset($_COOKIE['check_over21'])) {
			return;// wp_redirect( site_url() ); 
		} else if (!isset($_COOKIE['check_over21']) && $_COOKIE['check_over21'] == '') {
			
			$curr_page = cur_page_url();
			$splash_page = site_url() . '/age-check/';
			if ($curr_page == $splash_page) {
				$curr_page = site_url();
			}
			setcookie('check_over21', $curr_page, time()+1209600, COOKIEPATH, COOKIE_DOMAIN, false);
			$pos = strpos($check_redirect, 'wp-login.php'); // test for login otherwise go to Join
			if ($pos !== false) {
				 $check_redirect = get_bloginfo( 'siteurl' ) . 'wp-login.php';
				 //echo '<p>' . $check_redirect . '</p>';
				 wp_safe_redirect( $check_redirect ); 
			} else {
				wp_safe_redirect( $splash_page ); 
			}
		}
	}
}
/*
 * This goes in your functions file
 */
function cur_page_url() {
	$pageURL = 'http';
	if ($_SERVER["HTTPS"] == "on") {$pageURL .= "s";}
	$pageURL .= "://";
	
	if ($_SERVER["SERVER_PORT"] != "80") {
		$pageURL .= $_SERVER["SERVER_NAME"].":".$_SERVER["SERVER_PORT"].$_SERVER["REQUEST_URI"];
		} else {
		$pageURL .= $_SERVER["SERVER_NAME"].$_SERVER["REQUEST_URI"];
	}
	return $pageURL;
}

/* 
 * This goes in your page template.
 *
 */
add_action ('wp_head','check_lpage_hdr' );
function check_lpage_hdr() {
	echo '<style type="text/css">body{background-image:none !important;background-color:transparent !important;}</style>';
	echo '
	<script type="text/javascript">
	jQuery(document).ready(function($){
		function setCookie(name,value,days) {
			if (days) {
				var date = new Date();
				date.setTime(date.getTime()+(days*24*60*60*1000));
				var expires = "; expires="+date.toGMTString();
			}
			else var expires = "";
			document.cookie = name+"="+value+expires+"; path=/";
		};
		function deleteCookie(name) {
			setCookie(name,"",-1);
		}
		
		$("#over21 a").click(function(e){
			setCookie("check_over21", 1, 1);
			window.location = "'.get_bloginfo( 'siteurl' ).'";
			e.preventDefault();
		});
		
		$("#under21 a").click(function(e){
			deleteCookie("check_over21");
			window.location = "http://www.google.com";
			e.preventDefault();
		});
	});
	</script>';
}
remove_action ( 'genesis_loop','genesis_do_loop' );
add_action ( 'genesis_loop','check_landing_page_loop' );
function check_landing_page_loop() {
	echo '<h1>Age Check</h1>';
	echo '<div class="entry-content">';

	the_content();

	if ( isset( $_COOKIE['check_over21'] ) ) {
		 if (1 == $_COOKIE['check_over21'] ) {
			$age_redirect = get_bloginfo( 'siteurl' );
		} else {
			$pos = strpos( $age_redirect, 'wp-content' ); // test for bad link
			if ( false !== $pos ) {
				 $age_redirect = get_bloginfo( 'siteurl' );
			}
			echo '<p>'. $age_redirect . '</p>';
			echo '<p id="over21">I am <a href="#">Over 21</a></p>';
			echo '<hr />';
			echo '<p id="under21">I am <a href="#">Under 21</a></p>';
		}
	}
}