Subtracting time in PHP correctly - php

Question

I have used a few forms to establish a duration of time that a user has worked as well as get the amount of overtime they have worked. Problem is that I want to know how many hours can be billed in overtime and how many is normal time. Now its rather obvious, subtract overtime from total time,however I used the following script to obtain the time amounts:
$logtime = new CGenRs("SELECT time_id,
profile_id ,
user_number ,
start_time ,
end_time,
description,
exported,ovt_start_time,ovt_end_time, EXTRACT(hour FROM(end_time - start_time)) as diff,EXTRACT(minute FROM(end_time - start_time))as difference,EXTRACT(hour FROM(ovt_end_time-ovt_start_time)) as ovt_diff,EXTRACT(minute FROM(ovt_end_time-ovt_start_time)) as ovt_difference from adapt_profile_time where exported = 'f' order by user_number", $cao);
$logtime->first();
The Extract feature works well to show the times but when I start to subtract its where it gets a bit messy.
$tot_mins = 0;
$ovt_mins = 0;
}
$tot_mins = ($tot_mins + $logtime->valueof('diff') * 60) + $logtime->valueof('difference');
$ovt_mins = ($ovt_mins + $logtime->valueof('ovt_diff') * 60) + $logtime->valueof('ovt_difference');
$total_test= floor(($tot_mins / 60)-($ovt_mins / 60))." hours ".(($tot_mins % 60)-($ovt_mins % 60))." minutes ";
When using the echo $total_test it does the calculation but if the user has worked 7 hours 0 minutes which consists out of 3 hours 40 minutes overtime the result of the above calculation returns 3 hours -40 minutes. Which is wrong.
So where am I going wrong here?
I believe the problem lies with the EXTRACT hours and minutes not working well with the "-" "+" operators. I added a total colum in my table that adds the total time with the overtime (It should be subtracted but I did it to test) I used the following code:
<td><?php echo ($logtime->valueof('diff') + $logtime->valueof('ovt_diff')) . " " . "hours" . " ".(($logtime->valueof('difference') + $logtime->valueof('ovt_difference')))." "."minutes" ?></td>
The result was interesting. If user worked 3 hours 50 minutes of which it all was overtime, the result returned was 6 hours 100 minutes. So the addition is working, its just the values aren't recognized in a time format

Answer 1

As I stated in the comments, it is wise to use the DateTime classes for any date/time actions you want to do. Including getting the difference between times.
Check out this example:
// Create two new DateTime-objects...
$Date1 = new DateTime('2015-10-21T8:00:00');
$Date2 = new DateTime('2015-10-21T18:30:00');
// The diff-methods returns a new DateInterval-object...
$Diff = $Date2->diff($Date1);
// Call the format method on the DateInterval-object
echo $Diff->format('%h:%i');
The output from the code above should be "10:30"
From here on you can simply get the difference between the times and check if it is more then 8 hours. If it is, you can get your amount of overtime.

Answer 2

I eventually got it working. I changed my query to the following:
$logtime = new CGenRs("SELECT time_id,
profile_id ,
user_number ,
start_time ,
end_time,
description,
exported,ovt_start_time,ovt_end_time, EXTRACT(hour FROM(end_time - start_time)) as diff,EXTRACT(minute FROM(end_time - start_time))as difference ,EXTRACT(hour FROM(ovt_end_time-ovt_start_time)) as ovt_diff,EXTRACT(minute FROM(ovt_end_time-ovt_start_time)) as ovt_difference,EXTRACT(EPOCH FROM (end_time - start_time)) as super,EXTRACT(EPOCH FROM (ovt_end_time - ovt_start_time)) as spar FROM adapt_profile_time where exported = 'f' order by user_number", $cao);
$logtime->first();
As you can see I added the EXTRACT Epoch to the query for both the over time and the total work time.
I then added the next piece of code:
<td><?php $epoch_1 = $logtime->valueof('super');
$epoch_2 = $logtime->valueof('spar');
$diff_seconds = $epoch_1 - $epoch_2;
$diff_weeks = floor($diff_seconds / 604800);
$diff_seconds -= $diff_weeks * 604800;
$diff_days = floor($diff_seconds / 86400);
$diff_seconds -= $diff_days * 86400;
$diff_hours = floor($diff_seconds / 3600);
$diff_seconds -= $diff_hours * 3600;
$diff_minutes = floor($diff_seconds / 60);
$diff_seconds -= $diff_minutes * 60;
echo $diff_hours." "."hours ".$diff_minutes." minutes" ?></td>
<td>
And so I got the correct values to display in the table.
That being done I changed the code in my question to the following:
$tot_mins = 0;
$ovt_mins = 0;
$total_mens = ($logtime->valueof('super') /60 ) + ($logtime->valueof('spar')/60);
while (!$logtime->eof()) {
while (!$logtime->eof()) {
if ($curr_userno != $logtime->valueof('user_number')) {
$total_time = floor($tot_mins / 60) . " hours " . ($tot_mins % 60) . " minutes";
$total_ovt = floor($ovt_mins / 60) . " hours " . ($ovt_mins % 60) . " minutes";
$total_test = floor($total_mens/60)." hours ".($total_mens%60). " minutes";
And now its working.The values are adding up perfectly and carrying over when necessary.