php check for a valid date, weird date conversions

Question

Is there a way to check to see if a date/time is valid you would think these would be easy to check:

$date = '0000-00-00';
$time = '00:00:00';
$dateTime = $date . ' ' . $time;

if(strtotime($dateTime)) {
    // why is this valid?
}

what really gets me is this:

echo date('Y-m-d', strtotime($date)); 

results in: "1999-11-30",

huh? i went from 0000-00-00 to 1999-11-30 ???

I know i could do comparison to see if the date is either of those values is equal to the date i have but it isn't a very robust way to check. Is there a good way to check to see if i have a valid date? Anyone have a good function to check this?

Edit: People are asking what i'm running: Running PHP 5.2.5 (cli) (built: Jul 23 2008 11:32:27) on Linux localhost 2.6.18-53.1.14.el5 #1 SMP Wed Mar 5 11:36:49 EST 2008 i686 i686 i386 GNU/Linux

Answer 1

From php.net

<?php
function isValidDateTime($dateTime)
{
    if (preg_match("/^(\d{4})-(\d{2})-(\d{2}) ([01][0-9]|2[0-3]):([0-5][0-9]):([0-5][0-9])$/", $dateTime, $matches)) {
        if (checkdate($matches[2], $matches[3], $matches[1])) {
            return true;
        }
    }

    return false;
}
?>