Check time left before php session expires - php

Question

I need to build a php session expiry alert / stay logged in prompt for my website.
I have looked at dozens of examples but am confused so back to basics.
Is there a way to display a countdown for the default expiry time?
UPDATE 1
So far - to get a handle on the situation - I have:
echo '<p>This is the $_SESSION[\'expiretime\']: ' . $_SESSION['expiretime'] . '</p>';
echo '<p>This is the time(): ' . time() . '</p>';
$timeleft = time() - $_SESSION['expiretime'];
echo '<p>This is the time() MINUS the $_SESSION[\'expiretime\'] : ' . $timeleft . '</p>';
I'm not certain what the parameter $_SESSION['expiretime'] is but I found it in a thread and it looked interesting. Other than the number of seconds since 1970 I'm not sure what all of this tells me but may be useful for subsequent calcs.

Answer 1

You have to do something like
//Start our session.
session_start();
//Expire the session if user is inactive for 30
//minutes or more.
$expireAfter = 30;
//Check to see if our "last action" session
//variable has been set.
if(isset($_SESSION['last_action'])){
//Figure out how many seconds have passed
//since the user was last active.
$secondsInactive = time() - $_SESSION['last_action'];
//Convert our minutes into seconds.
$expireAfterSeconds = $expireAfter * 60;
//Check to see if they have been inactive for too long.
if($secondsInactive >= $expireAfterSeconds){
//User has been inactive for too long.
//Kill their session.
session_unset();
session_destroy();
} else {
echo("Expire in:");
echo($expireAfterSeconds - $secondsInactive);
}
}
$_SESSION['last_action'] = time();