Get time zone offset between two timezones for a given duration

Question

I wanted to know if there is a way to get the time zone offset for a given date range between two timezones for a given duration.

getTimezoneOffset(startDate,endDate,timezone1,timezone2){
    ...missing magic to go here...
}

should return the time zone offset which is valid for the a given duration. However if the offset changes, it should return the date range for which it's valid.

So I am looking at something like this:

getTimezoneOFfset("march 9 12 am", "march 15 12 am", "UTC", "US/NEW_YORK")

return value something like this

timezoneoffset[0]["range"]=[march 9 12am to march 11 2 am]
timezoneoffset[0]["offset"]=5
timezoneoffset[1]["range"]=[march 9 2 am to march 15 12 am]
timezoneoffset[1]["offset"]=4

I just don't want to calculate timezone offsets for every scheduled item for the given range. Was looking if there is some way to get a direct lookup for offsets if it's going to change.

I am working with PHP, but a solution in any language will be appreciated.

MySQL solution will also work as it will be more optimized to do this in MySQL.

Answer 1

Assuming that you have a newer version of php (5.2.0+) the DateTimeZone class is part of the PHP core and will let you use the getOffset() function to make these calculations. It will let you pass in a dateTime object and specify a timezone. If you do this for both your dates you should be able to calculate all of the pieces you're looking to grab. To use an example from php.net:

// Create two timezone objects, one for Taipei (Taiwan) and one for
// Tokyo (Japan)
$dateTimeZoneTaipei = new DateTimeZone("Asia/Taipei");
$dateTimeZoneJapan = new DateTimeZone("Asia/Tokyo");

// Create two DateTime objects that will contain the same Unix timestamp, but
// have different timezones attached to them.
$dateTimeTaipei = new DateTime(mktime([the date in question]), $dateTimeZoneTaipei);
$dateTimeJapan = new DateTime(mktime([the date in question]), $dateTimeZoneJapan);


// Calculate the GMT offset for the date/time contained in the $dateTimeTaipei
// object, but using the timezone rules as defined for Tokyo
// ($dateTimeZoneJapan).
$timeOffset = $dateTimeZoneJapan->getOffset($dateTimeTaipei);

// Should show int(32400) (for dates after Sat Sep 8 01:00:00 1951 JST).
print("Number of seconds Japan is ahead of GMT at the specific time: ");
var_dump($timeOffset);

print("<br />Number of seconds Taipei is ahead of GMT at the specific time: ");
var_dump($dateTimeZoneTaipei->getOffset($dateTimeTaipei));

print("<br />Number of seconds Japan is ahead of Taipei at the specific time: ");
var_dump($dateTimeZoneJapan->getOffset($dateTimeTaipei)
     -$dateTimeZoneTaipei->getOffset($dateTimeTaipei));

Answer 2

This working for me:

function Get_Timezone_Offset($remote_tz, $origin_tz = null) 
{
    if($origin_tz === null) 
    {
        if(!is_string($origin_tz = date_default_timezone_get())) {
            return false;
        }
    }
    $origin_dtz = new DateTimeZone($origin_tz);
    $remote_dtz = new DateTimeZone($remote_tz);
    $origin_dt  = new DateTime("now", $origin_dtz);
    $remote_dt  = new DateTime("now", $remote_dtz);
    $offset     = $origin_dtz->getOffset($origin_dt) - $remote_dtz->getOffset($remote_dt);
    return $offset;
}

To use it

echo Get_Timezone_Offset('America/New_York', 'Europe/Stockholm');

Source: http://php.net/manual/en/function.timezone-offset-get.php