<?php
function cookieplugin() {

	$cookie = wp_get_current_user();
	$site_id = [];
	$id = get_the_id();

	if(isset($_COOKIE['user'])) {
    	$site_id[] = $id;
	}
	else {
    	setcookie('user', $cookie, time() + 3600*24*100, "/");
    	$site_id[] = $id;
	}

}
add_action('wp_head', 'cookieplugin');
?>