Question

I am trying to determine the number of date intervals between two dates. The interval could be a number of months, days, hours or whatever the user has chosen.

At the moment I have a function using recursion, however, this will break if there have been more than 100 intervals between the two points, due to the recursive nesting limit.

private static function findCurrentInterval($initialStartTimestamp, $intervalStrtotimeFormat, $now = null, $period = 1)
{
    if (is_null($now)){
        $now = time();
    }

    $endOfCurrentInterval = strtotime($intervalStrtotimeFormat, $initialStartTimestamp);

    if ($now > $initialStartTimestamp && $now < $endOfCurrentInterval){
        return new self($period);
    }else{
        # increment the period ID tracking variable
        $period++;
        return self::findCurrentInterval($endOfCurrentInterval, $intervalStrtotimeFormat, $now, $period);
    }
}

All I need out of it is an integer value that represents which period of time intervals we are in currently, i.e. if it is set to a 7 day interval, and 20 days have passed between the start point and now, it would return ‘3’, because we’d be into the 3rd period.

Is there a way of doing this without recursion, perhaps using DateInterval?

N.B. this would be really straightforward if it was limited to days or hours – but it needs to support months, which can have variable lengths.

Answer 1

This seems to work:

function findCurrentInterval($number, $type, $start, $end){

    $dt1 = DateTime::createFromFormat('Y-m-d H:i:s', $start);
    $dt2 = DateTime::createFromFormat('Y-m-d H:i:s', $end);
    $diff = $dt1->diff($dt2);

    $numDays = (int) $diff->format('%a');
    $numMonths = (int) $diff->format('%m');
    $numYears = (int) $diff->format('%y');
    $numHours = (int) $diff->format('%h');

    if ($numYears > 0){
        $numMonths += ($numYears * 12);
    }

    $numHours += $numDays * 24;


    switch ($type){
        case 'hours':
            return floor($numHours / $number);
        break;
        case 'days':
            return floor($numDays / $number);
        break;
        case 'months':
            return floor($numMonths / $number);
        break;
        default:
            throw new Exception('Interval type '.$type.' not implemented.');
    }

}

Examples:

echo findCurrentInterval(3, 'hours', '2012-01-01 00:00:00', '2012-08-01 00:00:00');
echo findCurrentInterval(7, 'days', '2012-01-01 00:00:00', '2012-08-01 00:00:00');
echo findCurrentInterval(1, 'months', '2012-01-01 00:00:00', '2012-08-01 00:00:00');

Outputs:

1704
30
7

And:

echo findCurrentInterval(3, 'hours', '2011-01-01 00:00:00', '2012-08-01 00:00:00');
echo findCurrentInterval(7, 'days', '2011-01-01 00:00:00', '2012-08-01 00:00:00');
echo findCurrentInterval(1, 'months', '2011-01-01 00:00:00', '2012-08-01 00:00:00');

Outputs:

4624
82
19