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

Far from my best work... but here's some functions for working with string or unix time stamp.

/**
 * Takes a timestamp like "2016-10-01 17:59:01" and returns "2016-10-01 18:00"
 * Note: assumes timestamp is in UTC
 * 
 * @param $timestampString - a valid string which will be converted to unix with time()
 * @param int $mins - interval to round to (ex: 15, 30, 60);
 * @param string $format - the format to return the timestamp default is Y-m-d H:i
 * @return bool|string
 */
function roundTimeString( $timestampString, $mins = 30, $format="Y-m-d H:i") {
    return gmdate( $format, roundTimeUnix( time($timestampString), $mins ));
}

/**
 * Rounds the time to the nearest minute interval, example: 15 would round times to 0, 15, 30,45
 * if $mins = 60, 1:00, 2:00
 * @param $unixTimestamp
 * @param int $mins
 * @return mixed
 */
function roundTimeUnix( $unixTimestamp, $mins = 30 ) {
    $roundSecs = $mins*60;
    $offset = $unixTimestamp % $roundSecs;
    $prev = $unixTimestamp - $offset;
    if( $offset > $roundSecs/2 ) {
        return $prev + $roundSecs;
    }
    return $prev;
}