在PHP中间隔的舍入时间

Question

I want to convert times to rounded times.
Therefore I only want to use intervals in seconds. It works well for quarter hours and full hours. But not for days. Then it is messed up. But I can't understand why

This is my function:

function formatToMySQLTime($sTime,$iInterval){
    switch ($iInterval){
        case 1: // 15 minutes;
            $iDivider = 15 * 60;
            break;
        case 2: // 1 hour
            $iDivider = 60 * 60;
            break;
        case 3: // 1 day
            $iDivider = 60 * 60 * 24;
            break;
    }    
    $iRemainder = strtotime($sTime) % $iDivider;
    $iRoundTime = strtotime($sTime) - $iRemainder;    
    $sTime = date('Y-m-d H:i:s', $iRoundTime);
    return $sTime;
}

Here is the output:

echo formatToMySQLTime('2013-10-21 03:23:00',1);
2013-10-21 03:15:00

echo formatToMySQLTime('2013-10-21 03:23:00',2);
2013-10-21 03:00:00

echo formatToMySQLTime('2013-10-21 03:23:00',3);
2013-10-21 02:00:00

The third output is wrong, it should be 2013-10-21 00:00:00. What is my mistake?

Answer 1

You have timezone issue, because strtotime function is not timezone aware, and date is. Instead of setting global timezone, you can set it locally with appending UTC string to the $sTime variable, and instead of using date() use gmdate():

// it doesn't matter in which timezone your are, function works with UTC
date_default_timezone_set('Europe/Berlin');

function formatToMySQLTime($sTime, $iInterval) {
    switch ($iInterval){
        case 1: // 15 minutes;
            $iDivider = 15 * 60;
            break;
        case 2: // 1 hour
            $iDivider = 60 * 60;
            break;
        case 3: // 1 day
            $iDivider = 60 * 60 * 24;
            break;
    }
    $U = strtotime($sTime . ' UTC');
    $iRoundTime = $U - $U % $iDivider;    
    return gmdate('Y-m-d H:i:s', $iRoundTime);
}

echo formatToMySQLTime('2013-10-21 03:23:00',1);
echo formatToMySQLTime('2013-10-21 03:23:00',2);
echo formatToMySQLTime('2013-10-21 03:23:00',3);

Run code.

---

Update:

Instead of modifying function for every interval, you can make function a little more generic and readable, with the help of DateTime classes, like:

function formatToMySQLTime($sTime, $iInterval) {
    $dt = new DateTime($sTime, new DateTimezone('UTC'));
    $U = $dt->getTimestamp();

    $dt2 = clone $dt;
    $interval = DateInterval::createFromDateString($iInterval);
    $iDivider = $dt2->add($interval)->getTimestamp() - $U;

    $dt->setTimestamp($U - $U % $iDivider);
    return $dt->format('Y-m-d H:i:s');
}

echo formatToMySQLTime('2013-10-21 03:23:00', '15 minute');
echo formatToMySQLTime('2013-10-21 03:23:00', '1 hour');
echo formatToMySQLTime('2013-10-21 03:23:00', '1 day');

Run code.