[PHP]時間を15分刻みに変換する

覚え書きの殴り書き。 時間を15分刻みに変換する。切り上げ、切り捨てありです。

/*
 * dateBy15Minutes
 * @assert ("2001-03-10 17:16:18") == "2001-03-10 17:15:00"
 * @assert ("2001-03-10 17:00:00") == "2001-03-10 17:00:00"
 * @assert ("2001-03-10 17:59:59") == "2001-03-10 17:45:00"
 * @assert ("2001-03-10 17:40:18") == "2001-03-10 17:30:00"
 */

 protected function _dateBy15Minutes($mode = 'ceil',$time = NULL) {
  if (\is_null($time)) {
   $time = time();
  } else {
   $time = \strtotime($time);
  }
  if ($mode == 'ceil') {
   $minute = \sprintf("%02s", \ceil(\date('i') / 15) * 15);
  } else {
   $minute = \sprintf("%02s", \floor(\date('i') / 15) * 15);
  }
  $time_string = \date("Y-m-d H:i:s", \mktime(\date('H'), $minute));
  return $time_string;
 }