/**
* Calculates the offset of this time zone for a given Julian date. Accounts
* for daylight savings time if relevant and based on the date.
*
* @param float $jd Julian date to check for
* @return float Offset in hours including DST (if relevant)
*/
public function offset($jd)
{
// Is DST observed for this timezone? If no, return offset as is
if ($this->dst == false) {
return $this->offset;
}
// Get YMD for provided JD and day of year number (with fractional day)
IAU::Jd2cal($jd, 0, $y, $m, $d, $fd);
$dayN = static::dayOfYear($y, $m, $d) + $fd;
// DST begins at 2:00 a.m. on the second Sunday of March and...
IAU::Cal2jd($y, 3, 1, $djm0, $djm);
$dayB = static::dayOfYear($y, 2, 1) + 14 - static::weekDayNum($djm0 + $djm) + 2 / 24;
// ...ends at 2:00 a.m. on the first Sunday of November
IAU::Cal2jd($y, 11, 1, $djm0, $djm);
$dayE = static::dayOfYear($y, 11, 1) + 14 - static::weekDayNum($djm0 + $djm) + 2 / 24;
// Check if the given JD falls with in the DST range for that year
if ($dayN >= $dayB && $dayN < $dayE) {
return $this->offset + 1;
} else {
return $this->offset;
}
}
/**
* Sets the date for this instance
*
* @param int $year Year
* @param int $month Month
* @param int $day Day
* @return static
*/
public function setDate($year, $month, $day)
{
$status = IAU::Cal2jd((int) $year, (int) $month, (int) $day, $djm0, $djm);
$this->checkDate($status);
// Check date is valid
$this->jd = $djm0 + $djm;
// Only set JD, keep day frac to save time
return $this;
}
