PHP Count Down Expiry Button or Link - php

Question

I'm trying to create a button or link that will expire after 1 hour.
I'm setting the time the visitor hit the page with a cookie.
Most of the code examples I have seen only give the time that has passed and not the time left.
example: Link will expire in 0 hours, 30, mins and 34 seconds
This is just some rough code :
//Setting cookie example
setcookie('previous_time', time(), time()+3600*1);
$current_time = time();
$previous_time = $_COOKIE['previous_time'];
$time_diff = $current_time-$previous_time;
This is where I'm stuck, I have no idea how to convert the $time_diff timestamp
into a format like "expire in 0 hours, 30, mins and 34 seconds"
Many thanks.

Answer 1

To format your time difference, just do some math, since your $time_diff is just the number of seconds between the two times:
$hours = floor( $time_diff / 3600);
$minutes = floor( ($time_diff / 60) % 60);
$seconds = $time_diff % 60;
echo "$hours hours, $minutes minutes, $seconds seconds\n";
So, a value of 20712 would produce :
5 hours, 45 minutes, 12 seconds

Answer 2

Using your formula comparing timestamps, the difference is in seconds.
So, $time_diff / 60 gets you minutes; divide by another 60 to get hours; etc.

Answer 3

I agree with nickb that cookie based is tamper-able, but saying you mark the first visit somehow for an hour ahead when the link will expire:
// set when we are counting down to
setcookie('expires_at', time()+3600, time()+3600);
// we are counting down not up (for "expires in" not "valid since" logic)
$time_diff = $_COOKIE['expires_at'] - time();
$minutes = floor($time_diff / 60);
$seconds = floor($time_diff % 60);
// zero hours since the link will only be valid for one hour max
echo sprintf('expire in 0 hours, %d mins and %d seconds', $minutes, $seconds);
Then you can do:
if($time_diff > 0){
echo '...';
}