Relative Time Vs Absolute Time In PHP - php

Question

Please check the following examples:
$date1 = strtotime("tomorrow 4:00 PM");
$date2 = strtotime("16:00:00");
$date3 = strtotime("10 hours");
$date4 = strtotime("+1 day");
echo date("Y m d H:i:s",$date1)."<br>";
echo date("Y m d H:i:s",$date2)."<br>";
echo date("Y m d H:i:s",$date3)."<br>";
echo date("Y m d H:i:s",$date4)."<br>";
It gives me the output as below:
2013 06 10 16:00:00
2013 06 09 16:00:00
2013 06 09 20:50:25
2013 06 10 10:50:25
I am considering first two example($date1 and $date2) as absolute data and the last two as relative date. Now, with only given the $date1/$date2/$date3/$date4 variables, is it possible to say whether it is relative time or an absolute time please?
I did get a solution on another thread: PHP datetime string differentiation
But that worked until I considered the 2nd example($date2 as an absolute value), where it doesn't work. Also, may suggested for regular expression checks, but that doesn't seem reliable either.
I was just wondering if php had some integrated way to tell this either from its functions or DateTime objects. I searched for, but didn't found anything.
Looking forward to listen for your suggestions/feedbacks/possible solutions. Thanks.

Answer 1

There is no direct way, AFAIK but there is a trick that you can use with the second parameter to the strtotime function.
function is_absolute_time($time_string) {
$time_shift = time() + 60; // 1 min from now
$time_normal = strtotime($time_string);
$time_shifted = strtotime($time_string, $time_shift);
return $time_normal == $time_shifted;
}
The rationale is simple: If the time is absolute, a 1 min difference won't change the calculation by strtotime and both $time_normal and $time_shifted will be same. For relative times, however, the difference will be one minute (the value in $time_shift variable).
There is a caveat with this code though. This function will return FALSE even for absolute times (but not absolute dates) less than 1 minute from midnight. You can minimize this by changing $time_shift to:
$time_shift = time() + 5; // 5 seconds from now.
This code will now work properly until 5 seconds from midnight. I think you can go safely to as low as 2. There is an edge case that 1 second in future might not work.
To fix this problem altogether, you can try a different approach:
function is_absolute_time($time_string) {
$epoch = 0; // Epoch
$time_shift = 60; // 1 min from epoch
$time_normal = strtotime($time_string, $epoch);
$time_shifted = strtotime($time_string, $time_shift);
return $time_normal == $time_shifted;
}
You can try this last solution directly. I am just building up the reason for the solution throughout this post.

Answer 2

Given only the value 2013 06 10 16:00:00 the answer is simple: it's absolute. Whether this absolute timestamp was created as "absolute" timestamp or based on relation to another date is impossible to tell. All you have is "2013 06 10 16:00:00", there's no "residual relativeness" or anything of that kind still in it.
Even this is relative to the supposed birth of Christ though, which is relative to the earth floating around in space since the Big Bang... *trollface*