Update Google API V3 script to allow use of refresh token - php

Question

I am using the following code which was largely lifted from this tutorial - http://www.daimto.com/google-oauth2-php/
I have added the line client->setAccessType("offline"); in order to receive a refresh token from Google which I can see coming through from print "Access from google: " . $_SESSION['token'];.
I'm struggling to understand how to use the refresh token in order to get authorisation. What I'd ideally like to is update this script to
- use a refresh token if one is available, or
- present the existing "Connect Me" link if one is not
I plan to store the refresh token in a DB eventually, however to get it working initially I will just hard code.
Any help is much appreciated!
<?php
set_include_path('src');
require_once 'Google/Client.php';
require_once 'Google/Service/Calendar.php';
session_start();
$client = new Google_Client();
$client->setApplicationName("Client_Library_Examples");
$client->setDeveloperKey("XXXXXXXXXXXXXXXXXXXX");
$client->setClientId('XXXXXXXXXXXXXXXXXXXX');
$client->setClientSecret('XXXXXXXXXXXXXXXXXXXX');
$client->setRedirectUri('XXXXXXXXXXXXXXXXXXXX');
$client->setAccessType("offline");
$client->setScopes(array('https://www.googleapis.com/auth/calendar'));
//For loging out.
if ($_GET['logout'] == "1") {
unset($_SESSION['token']);
}
// Step 2: The user accepted your access now you need to exchange it.
if (isset($_GET['code'])) {
$client->authenticate($_GET['code']);
$_SESSION['token'] = $client->getAccessToken();
$redirect = 'http://' . $_SERVER['HTTP_HOST'] . $_SERVER['PHP_SELF'];
header('Location: ' . filter_var($redirect, FILTER_SANITIZE_URL));
}
// Step 1: The user has not authenticated we give them a link to login
if (!$client->getAccessToken() && !isset($_SESSION['token'])) {
$authUrl = $client->createAuthUrl();
print "<a class='login' href='$authUrl'>Connect Me!</a>";
}
// Step 3: We have access we can now create our service
if (isset($_SESSION['token'])) {
print "<a class='logout' href='".$_SERVER['PHP_SELF']."?logout=1'>LogOut</a><br>";
$client->setAccessToken($_SESSION['token']);
$service = new Google_Service_Calendar($client);
}
print "<br>";
print "Access from google: " . $_SESSION['token'];
print "<br><br>";
require_once 'calendar_app.php';
?>