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

PHP does have a DateTime class and a whole slough of methods that it provides. You could use these if you like, but I find it easier to use the built-in date() and strtotime() functions.

Here's my solution:

// Assume $timestamp has the original timestamp, i.e. 2012-03-09 16:23:41

$day = date( 'Y-m-d', $timestamp ); // $day is now "2012-03-09"
$hour = (int)date( 'H', $timestamp ); // $hour is now (int)16
$minute = (int)date( 'i', $timestamp ); // $minute is now (int)23

if( $minute < 30 ){
  $windowStart = strtotime( "$day $hour:00:00" );
  $windowEnd   = strtotime( "$day $hour:30:00" );
} else {
  $windowStart = strtotime( "$day $hour:30:00" );
  if( ++$hour > 23 ){
    // if we crossed midnight, fix the date and set the hour to 00
    $day = date( 'Y-m-d', $timestamp + (24*60*60) );
    $hour = '00';
  }
  $windowEnd   = strtotime( "$day $hour:00:00" );
}

// Now $windowStart and $windowEnd are the unix timestamps of your endpoints

There are a few improvements that can be made on this, but that's the basic core.

[Edit: corrected my variable names!]

[Edit: I've revisited this answer because, to my embarrassment, I realized that it didn't handle the last half-hour of a day correctly. I've fixed that issue. Note that $day is fixed by adding a day's worth of seconds to the timestamp -- doing it this way means we don't have to worry about crossing month boundaries, leap days, etc. because PHP will format it correctly for us regardless.]