TOTP::expiresIn() is not correct when setting epoch

[tomme87]

Version(s) affected

11.3.0

Description

Seams like epoch is not taken into consideration when doing TOTP::expiresIn()

How to reproduce

$clock = new MockClock('2025-02-24 15:10:33');
$now = $clock->now();
$totp = TOTP::generate($clock);
$totp->setPeriod(1000);
$totp->setEpoch($now->getTimestamp());
echo $totp->expiresIn()

This returns 167, but since i set the epoch to the current timestamp it should be 1000.

The actual expiration is correct though.

$clock->sleep(999);
echo $totp->verify($code) ? 'yes' : 'no';
$clock->sleep(1);
echo $totp->verify($code) ? 'yes' : 'no';

This returns yes and no on the second echo.

Possible Solution

I think the correct expiresIn should be (?)

$totp->getPeriod() - (($clock->now()->getTimestamp() - $totp->getEpoch()) % $totp->getPeriod())

Additional Context

No response

[Spomky]

Hello @tomme87,

Indeed the returned value does not consider the epoc parameter.
Would you mind to create a PR to fix this (with a test if possible)?

Many thanks.
Regards.