Generate Client IDs

cid.php

<?php
header("Cache-Control: no-cache, must-revalidate"); 
header("Pragma: no-cache");
session_start();

//no cookie, no session
if ((!isset($_COOKIE['cid'])) && (!isset($_SESSION['cid']))) {
	$_SESSION['cid'] = sprintf( '%04x%04x-%04x-%04x-%04x-%04x%04x%04x',
		mt_rand( 0, 0xffff ), mt_rand( 0, 0xffff ),
		mt_rand( 0, 0xffff ),
		mt_rand( 0, 0x0fff ) | 0x4000,
		mt_rand( 0, 0x3fff ) | 0x8000,
		mt_rand( 0, 0xffff ), mt_rand( 0, 0xffff ), mt_rand( 0, 0xffff )
	);
}

//cookie prior session
if (isset($_COOKIE['cid'])) {
	$_SESSION['cid'] = $_COOKIE['cid'];
}

//update cookie
if (isset($_SESSION['cid'])) {
	setcookie("cid", $_SESSION['cid'], time()+3600*24*365);
}

$cid = $_SESSION['cid']; 

if ($_GET['return']=="cid") {
	echo $cid;
}

Session.php

<?php

/*
 * Call like
 * Session->start( $unique );
 */

class Session{

	// hook into WordPress to start sessions.
	public function start( $unique = false ) {
	
		// only set no-cache headers if the session is supposed to be unique.
		if( $unique === true )
			add_action( 'send_headers', array( $this, 'set_headers' );
		}
		
		// set a unique client_id.
		add_action( 'wp', 'set_client_id' );
	}
	
	public function set_headers() {
		add_header( "Cache-Control: no-cache, must-revalidate" ); 
		add_header( "Pragma: no-cache" );
		add_action( 'llms/session/client_id/set', array( $this, 'start_unique_session' );
	}

	public function set_client_id() {
		
		// this will have to not run if you'd want to have anonymity
		$session_client_id = filter_var( $_SESSION[ 'llms_client_id' ] );

		$cookie_client_id = filter_input( INPUT_COOKIE, 'llms_client_id' );

		// no cookie, no session
		if( ! empty( $session_client_id ) && ! empty( $cookie_client_id ) ){
			$_SESSION[ 'llms_client_id' ] = $session_client_id = wp_generate_uuid4();
		}

		if( ! empty( $cookie_client_id ) ){

			$_SESSION[ 'llms_client_id' ] =  $session_client_id =  $cookie_client_id;
		}

		if( ! empty( $session_client_id ) ){

			setcookie( 'llms_client_id', $session_client_id, time() + YEAR_IN_SECONDS);
		}
		
		do_action( 'llms/session/client_id/set', $session_client_id );
	}
	
	function start_unique_session( $session_client_id ) {
		
		$session_id = filter_var( $_SESSION[ 'llms_session_id' ] );
		
		// this session has already started
		if( ! empty( $session_id ) ){
			return;
		}
	
		global $llms;
		
		$current_user = $llms->who_is;
		
		$_SESSION[ 'llms_session_id' ] = $session_id = wp_generate_uuid4();
		
		do_action( 'llms/session/started', $session_id );
		
		do_action( "llms/session/{$llms->who_is->persona_type}/started", $session_id );
	}
	
}