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<?php
/*
* Get the offset of a timezone
*/
function getTimezoneOffset($timezone)
{
$tz = new DateTimeZone($timezone);
$utc = new DateTimeZone('UTC');
return $tz->getOffset(new DateTime('now', $utc));
}
/*
* Prettify an offset
*/
function getPrettyOffset($offset)
{
$offset_prefix = $offset < 0 ? '-' : '+';
$offset_formatted = gmdate('H:i', abs($offset));
return 'UTC'.$offset_prefix.$offset_formatted;
}
/*
* Generate the timezone list
*/
function generateTimezoneList()
{
$regions = [
DateTimeZone::AFRICA,
DateTimeZone::AMERICA,
DateTimeZone::ANTARCTICA,
DateTimeZone::ASIA,
DateTimeZone::ATLANTIC,
DateTimeZone::AUSTRALIA,
DateTimeZone::EUROPE,
DateTimeZone::INDIAN,
DateTimeZone::PACIFIC,
];
$timezones = [];
foreach ($regions as $region)
{
$timezones = array_merge( $timezones, DateTimeZone::listIdentifiers( $region ) );
}
$timezone_offsets_summer = [];
$timezone_offsets_winter = [];
foreach ($timezones as $timezone)
{
$tz = new DateTimeZone($timezone);
$utc = new DateTimeZone('UTC');
$timezone_offsets_summer[$timezone] = $tz->getOffset(new DateTime('first day of August', $utc));
$timezone_offsets_winter[$timezone] = $tz->getOffset(new DateTime('first day of December', $utc));
}
// sort timezone by timezone name
ksort($timezone_offsets_summer);
ksort($timezone_offsets_winter);
$timezone_list = [];
foreach ($timezone_offsets_summer as $timezone => $offset)
{
$pretty_summer_offset = getPrettyOffset($offset);
$pretty_winter_offset = getPrettyOffset($timezone_offsets_winter[$timezone]);
$split = explode("/", $timezone);
$timezone_list[$timezone] = "$split[1]/$split[0] (Summer ${pretty_summer_offset} - Winter ${pretty_winter_offset})";
}
ksort($timezone_list);
return $timezone_list;
}