How to round unix timestamp up and down to nearest half hour?

Question

Ok so I am working on a calendar application within my CRM system and I need to find the upper and lower bounds of the half an hour surrorunding the timestamp at which someb

Answer 1

This is a solution using DateTimeInterface and keeping timezone information etc. Will also handle timezones that are not a multiple of 30 minutes offset from GMT (e.g. Asia/Kathmandu).

/**
 * Return a DateTimeInterface object that is rounded down to the nearest half hour.
 * @param \DateTimeInterface $dateTime
 * @return \DateTimeInterface
 * @throws \UnexpectedValueException if the $dateTime object is an unknown type
 */
function roundToHalfHour(\DateTimeInterface $dateTime)
{
    $hours = (int)$dateTime->format('H');
    $minutes = $dateTime->format('i');

    # Round down to the last half hour period
    $minutes = $minutes >= 30 ? 30 : 0;

    if ($dateTime instanceof \DateTimeImmutable) {
        return $dateTime->setTime($hours, $minutes);
    } elseif ($dateTime instanceof \DateTime) {
        // Don't change the object that was passed in, but return a new object
        $dateTime = clone $dateTime;
        $dateTime->setTime($hours, $minutes);
        return $dateTime;
    }
    throw new UnexpectedValueException('Unexpected DateTimeInterface object');
}

You'll need to have created the DateTime object first though - perhaps with something like $dateTime = new DateTimeImmutable('@' . $timestamp). You can also set the timezone in the constructor.