DateTime::add adds hours even when interval should only be seconds - php

Question

This comes from my previous question on getting the average time interval over a specified data set, [located here][1]. I'll post the entire function again:
function getATBData($siteID, $fromDate, $toDate)
{
global $pdo;
$ATBarray = array();
$maxATB;
$minATB;
$avgATB;
$totalATB=new DateTime("#0");
$totalEvents=0;
$timetable;
$query = "SELECT id, siteID, start_time, end_time FROM atb_log WHERE siteID=:siteID AND (start_time BETWEEN :fromDate AND :toDate) AND (end_time BETWEEN :fromDate AND :toDate)";
$stmt = $pdo->prepare($query);
$stmt->bindParam(":siteID", $siteID);
$stmt->bindParam(":fromDate", $fromDate);
$stmt->bindParam(":toDate", $toDate);
$stmt->execute();
foreach ($stmt as $row)
{
$timeDiff = date_diff(new DateTime($row['start_time']),new DateTime($row['end_time']), true); //force absolute
if(!isset($maxATB) OR dateIntervalInSeconds($timeDiff) > dateIntervalInSeconds($maxATB))
$maxATB = $timeDiff;
if(!isset($minATB) OR dateIntervalInSeconds($timeDiff) < dateIntervalInSeconds($minATB))
$minATB = $timeDiff;
$totalATB->add($timeDiff);
echo "added " . $timeDiff->format("%H:%I:%S") . " total is now: " . $totalATB->format("H:i:s") . "<br />";
$totalEvents++;
}
if($totalEvents!=0)
{
$avgATB = average_time($totalATB->format("H:i:s"),$totalEvents,0);
}
else
{
$avgATB=0;
$maxATB=new DateInterval('PT0S');
$minATB=new DateInterval('PT0S');
}
//$avgSeconds = new DateInterval("PT" . $avgATB . "S");
$ATBarray['max'] = $maxATB->format("%H:%I:%S");
$ATBarray['min'] = $minATB->format("%H:%I:%S");
$ATBarray['avg'] = $avgATB;
$ATBarray['total'] = $totalATB->format("H:i:s");
$ATBarray['events'] = $totalEvents;
return $ATBarray;
}
Given this function, I have added an output statement to try to debug why I was getting such a large time interval for my total time (when most of the values are a small number of seconds) and this is what it's outputting:
added 00:00:02 total is now: 01:00:02
added 00:00:00 total is now: 02:00:02
added 00:00:01 total is now: 03:00:03
added 00:00:01 total is now: 04:00:04
added 00:00:00 total is now: 05:00:04
added 00:00:02 total is now: 06:00:06
added 00:00:00 total is now: 07:00:06
and so on. So it seems like, despite the time to be added only being a couple seconds, it adds an hour every time. The call to add() on $timeDiff above is how I'm adding.
So the question is - is there a different way to call the add() function such that it will only add the seconds? Am I calling it incorrectly?

Answer 1

Hm, average difference in seconds, why that PHP swath of code if your database can give it to you:
SELECT
SEC_TO_TIME(MAX(TIME_TO_SEC(TIMEDIFF(end_time,start_time)))) AS max_timediff,
SEC_TO_TIME(MIN(TIME_TO_SEC(TIMEDIFF(end_time,start_time)))) AS min_timediff,
SEC_TO_TIME(AVG(TIME_TO_SEC(TIMEDIFF(end_time,start_time)))) AS avg_timediff,
SEC_TO_TIME(SUM(TIME_TO_SEC(TIMEDIFF(end_time,start_time)))) AS sum_timediff,
COUNT(id) as total_events
FROM atb_log
WHERE
siteID=:siteID
AND start_time > :fromDate
AND end_time < :toDate
Format those min/max/avg/sum of seconds as you like.

Answer 2

As I wrote in the answer to your other question, this is a DST (Daylight Savings Time) problem. In the U.S., DST has already begun; in Europe not.
Try this code:
timecheck("Europe/Amsterdam");
timecheck("America/Los_Angeles");
function timecheck($timezone) {
date_default_timezone_set($timezone);
$totalATB=new DateTime("#0");
$t1 = "2014-01-01 17:30:00";
$t2 = "2014-01-01 17:35:00";
$dt1 = new DateTime($t1);
$dt2 = new DateTime($t2);
$timeDiff = date_diff($dt1, $dt2, true);
printf("[%s] Starting with with: %s\n", $timezone, $totalATB->format("H:i:s"));
$totalATB->add($timeDiff);
printf("[%s] added %s, total is now: %s\n", $timezone, $timeDiff->format("%H:%I:%S"), $totalATB->format("H:i:s"));
}
The output:
[Europe/Amsterdam] Starting with with: 00:00:00
[Europe/Amsterdam] added 00:05:00, total is now: 00:05:00
[America/Los_Angeles] Starting with with: 00:00:00
[America/Los_Angeles] added 00:05:00, total is now: 01:05:00