Question

I am trying to write a calendar in PHP. In week view, I want my events to be listed like iCal, where simultaneous events reduces their width to half size.

I have an extremely hard time figuring this one out though, so I hope you can help me. What I want is that if one event is overlapping another, it should set [split] => true on both event arrays – or something in that direction (read: I am unsure whether this is the most efficient solution). Then I can check for split == true in the foreach loop which prints out the events.

Here is an example array containing two simultaneous events:

$events = array(
  array(
    "id" => 21,
    "start" => 1242219600,
    "end" => 1242237600,
    "title" => "foo",
    "split" => false
  ),
  array(
    "id" => 22,
    "start" => 1242223200,
    "end" => 1242234000,
    "title" => "foo",
    "split" => false
  )
);

$events = someFunctionToOffsetEvents($events);

How would you solve this one?

Answer 1

I’ve had to deal with date collision issues alot lately, and the best I’ve been able to come up with is:

date1.start < date2.end and date1.end > date2.start = collision

This simple formula will account for all of the following situations:

--same for all situations:
date1.start = 1/1/2009
date1.end = 1/10/2009

--Start date is in first dates range:
date2.start = 1/9/2009
date2.end = 2/10/2009

--End date is in first dates range:
date2.start = 12/10/2008
date2.end = 1/3/2009

--Start & End date is inside first dates range:
date2.start = 1/2/2009
date2.end = 1/3/2009

--First date is inside of second dates range:
date2.start = 12/1/2008
date2.end = 2/1/2009

$date1 = array('start' => '2009-01-05', 'end' => '2009-01-10');
$date2 = array('start' => '2009-01-01', 'end' => '2009-01-04'); // end inside one
$date3 = array('start' => '2009-01-04', 'end' => '2009-01-15'); // start inside one
$date4 = array('start' => '2009-01-01', 'end' => '2009-01-15'); // one inside me
$date5 = array('start' => '2009-01-04', 'end' => '2009-01-05'); // inside one

function datesCollide($date1, $date2)
{
    $start1TS = strtotime($date1['start']);
    $end1TS = strtotime($date1['end']);
    $start2TS = strtotime($date2['start']);
    $end2TS = strtotime($date2['end']);

    if ($start1TS <= $end2TS && $end1TS >= $start2)
    {
        return true;
    }

    return false;
}

Based on your comment this is probably the solution you are looking for:
Note that this solution isn’t very optimized, and should only be used for figuring out a better solution. Never trust code from the web.

$events = array(
  array(
        "id" => 21,
        "start" => 1242219600,
        "end" => 1242237600,
        "title" => "foo",
        "split" => false
  ),
  array(
        "id" => 22,
        "start" => 1242223200,
        "end" => 1242234000,
        "title" => "foo",
        "split" => false
  )
);

foreach ($events as $key => $event)
{
    $events[$key]->split = dateCollisionCheck($event, $events);
}

function dateCollisionCheck(&$event, &$eventList)
{
    foreach ($eventList as $checkEvent)
    {
        if ($event->id != $checkEvent->id)
        {
            if ($event->start <= $checkEvent->end && $event->end >= $checkEvent->start)
            {
                return true; // return as soon as we know there is a collision
            }
        }
    }

    return false;
}

*Code has not been tested