Check if time is between two times, gives false answers - php

Question

<?php
$saturday = array(
'00:00 - 01:00' => 'Nightshow',
'01:00 - 02:00' => 'Nightshow',
'02:00 - 03:00' => 'Nightshow',
'03:00 - 04:00' => 'Nightshow',
'04:00 - 05:00' => 'Nightshow',
'05:00 - 06:00' => 'Early birds',
'06:00 - 07:00' => 'Early birds',
'07:00 - 08:00' => 'Cox n Crendor in the morning',
'08:00 - 09:00' => 'Cox n Crendor in the morning',
...
'23:00 - 24:00' => 'John late night'
);
foreach($saturday as $timeD => $show){
if(!empty($timeD) && isset($timeD)){
$timesplit = explode(' -', $timeD);
if (time() > strtotime('today '. $timesplit[0]) && time() < strtotime('today '. $timesplit[1])) {
echo $show;
}
}
}
?>
Hello again Stackoverflow!
I have an array, containing times of the day (24h format) that represents a schedule. What I'm trying to do, is check wich show is currently on. What I've tried above didn't work - Times turned out to be a few hours off or they would be completely wrong, not even in a certain order. I don't understand what's wrong. How do I solve this?
Thanks in advance!

Answer 1

I believe you ran into some basic timezone problem.
Timezone Basic
Timezone conversion could be frustrating, but once you get used to it, it's pretty straight forward.
When we deal with time, we also need to be careful with functions like strtotime() and date(). These two functions are affected by timezone settings. When I say timezone setting, I mean the value date.timezone in your php.ini.
Take, for example, I set date.timezone = Asia/Singapore, and it's a UTC+8 timezone:
Let's say UTC time now is 2013-02-05 00:00:00 UTC and timestamp should be 1360022400:
time() will gives me 1360022400
strtotime('2013-02-05 00:00:00') will gives me 1359993600 (or -28800, or -8 hours!)
Notice how strtotime behaves? It actually uses the fact that the PHP environment is in UTC+8 timezone and thinks that the datetime you had specified is in a +8 timezone, and hence it pushed back 8 hours for you, to correctly represent it in UTC timestamp. This is where the problem is.
Solution
Usually, what I will do (perhaps someone can offer a better solution?) is to hard append a UTC behind the ambiguous datetime and force us to calculate everything in UTC timezone. So simply do this:
strtotime('2013-02-05 00:00:00 UTC')
will now gives you 1360022400, or exactly 00:00:00 in UTC time. This is especially good when you do time sensitive calculation when time() is returning you a real UTC timestamp.
Some notes:
time() will always give you UTC timestamp regardless of timezone setting.
strtotime() will always affected by timezone setting so if you are doing time sensitive comparison, try to make sure they are all in UTC.
date() as well, affected by timezone setting, where date('Y-m-d H:i:s', 1360022400) will gives you 2013-02-05 08:00:00 and to overcome this we use gmdate('Y-m-d H:i:s', 1360022400) instead.
Your Question
So since it seems like you are dealing with time-sensitive decision here, one question, do I need to see the same result as you if I live in a different timezone with you?
If we (I and you) need to see the exact same result, then you should do this:
//Let's say the timezone required for that decision made is UTC+6
$event_timezone_offset = 6 * 3600;
foreach($saturday as $timeD => $show){
if(!empty($timeD)){ //you don't need isset here as !empty taken care of it
list($startTime, $endTime) = explode(' - ', $timeD);
$start = strtotime('today '.$startTime.' UTC') - $event_timezone_offset;
$end = strtotime('today '.$endTime.' UTC') - $event_timezone_offset;
$now = time();
if ($start <= $now && $now < $end) { //notice the inclusive <=
echo $show;
}
}
For the line strtotime('today '.$startTime.' UTC') - $event_timezone_offset;, let's step through:
Let's assume the local time now is 07:00 (UTC+6) and you should see 'Cox n Crendor..':
time() will gives you the exact UTC timestamp of 2013-09-21 01:00:00 UTC
strtotime('today 07:00 UTC') will gives you the timestamp of 2013-09-21 07:00:00 UTC
and once you do - $event_timezone_offset, you get a time of 2013-09-21 01:00:00 UTC
so if ($start <= $now) will then be true, and you should see 'Cox n Crendor..'
If I and you need to get a different result based on our respective local timestamp, you will then need to either sniff user's timezone using javascript, or ask them to set a timezone through some backend settings, and use the same logic to determine the result, by setting $event_timezone_offset = $user_timezone_offset.
I hope this is not too confusing but it's really fun dealing with all these maths.

Answer 2

(You will have to replace $fake_timestamp with the current timestamp time() later in your script ... but I needed it that way for testing.)
<?php
$saturday = array(
'00:00 - 01:00' => 'Nightshow',
'01:00 - 02:00' => 'Nightshow',
'02:00 - 03:00' => 'Nightshow',
'03:00 - 04:00' => 'Nightshow',
'04:00 - 05:00' => 'Nightshow',
'05:00 - 06:00' => 'Early birds',
'06:00 - 07:00' => 'Early birds',
'07:00 - 08:00' => 'Cox n Crendor in the morning',
'08:00 - 09:00' => 'Cox n Crendor in the morning',
'23:00 - 24:00' => 'John late night'
);
//$current_day_timestamp = gettimeofday(); //bug? returns time(), not day!time
$current_day_timestamp = strtotime('TODAY');
//print 'Current day time: '.$current_day_timestamp.'<br />';
//Trying to "find" Early birds 05:00-06.00, setting "current time" to 05:30
$fake_timestamp = $current_day_timestamp + 5.5 * 3600;
//print 'fake time: '.$fake_timestamp.'<br />';
foreach ($saturday AS $hours => $show) {
$hours = explode(' - ', $hours);
$show_start = strtotime($hours[0]);
$show_end = strtotime($hours[1]);
if ($show_start < $fake_timestamp AND $show_end > $fake_timestamp) {
print $show;
}
//print $show.'<hr />';
//print 'show start: '.$show_start.'<br />';
//print 'show end: '.$show_end.'<br /><br />';
}
?>