Generate timezones list array

timezone-selectbox.php

<?php
function getTimezones(): array
{
    $timezones = \DateTimeZone::listIdentifiers();

    $options = [];
    $lastRegion = '';
    if (is_array($timezones)) {
        foreach ($timezones as $key => $timezone) {
            $DateTimeZone = new \DateTimeZone($timezone);
            $expTimezone = explode('/', $timezone);
            if (isset($expTimezone[0])) {
                if ($expTimezone[0] !== $lastRegion) {
                    $lastRegion = $expTimezone[0];
                }
                $getOffset = $DateTimeZone->getOffset(new \DateTime());
                $offset = ($getOffset < 0 ? '-' : '+');
                $offset .= gmdate('H:i', abs($getOffset));
                $options[$expTimezone[0]][$timezone] = [
                    'name' => $timezone,
                    'offset' => $offset,
                ];
                unset($getOffset, $offset);
            }
            unset($DateTimeZone, $expTimezone);
        }// endforeach;
        unset($key, $timezone);
    }

    unset($lastRegion, $timezones);

    return $options;
}


$options = getTimezones();


if (is_array($options)) {
    echo '<select name="timezone">' . PHP_EOL;
    foreach ($options as $optgroup => $items) {
        echo '    <optgroup label="' . $optgroup . '">' . PHP_EOL;
        if (is_array($items)) {
            foreach ($items as $key => $item) {
                echo '        <option value="' . $key . '">';
                echo $item['name'] . ' (UTC ' . $item['offset'] . ')';
                echo '</option>' . PHP_EOL;
            }// endforeach;
            unset($item, $key);
        }
        echo '    </optgroup>' . PHP_EOL;
    }// endforeach;
    unset($items, $optgroup);
    echo '</select>' . PHP_EOL;
}
unset($options);
/*
<select name="timezone">
    <optgroup label="Africa">
        <option value="Africa/Abidjan">Africa/Abidjan (UTC +00:00)</option>
        <option value="Africa/Accra">Africa/Accra (UTC +00:00)</option>
        ...
    </optgroup>
</select>
*/

timezoneslist.php

<?php
$timezones = \DateTimeZone::listIdentifiers();


$options = [];
$lastRegion = '';


if (is_array($timezones)) {
    foreach ($timezones as $key => $timezone) {
        $DateTimeZone = new \DateTimeZone($timezone);
        $expTimezone = explode('/', $timezone);
        if (isset($expTimezone[0])) {
            if ($expTimezone[0] !== $lastRegion) {
                $lastRegion = $expTimezone[0];
            }
            $getOffset = $DateTimeZone->getOffset(new \DateTime());
            $offset = ($getOffset < 0 ? '-' : '+');
            $offset .= gmdate('H:i', abs($getOffset));
            $options[$expTimezone[0]][$timezone] = [
                'name' => $timezone,
                'offset' => $offset,
            ];
            unset($getOffset, $offset);
        }
        unset($DateTimeZone, $expTimezone);
    }// endforeach;
    unset($key, $timezone);
}


unset($lastRegion, $timezones);


print_r($options);
/*
Array
(
    [Africa] => Array
        (
            [Africa/Abidjan] => Array
                (
                    [name] => Africa/Abidjan
                    [offset] => +00:00
                )

            [Africa/Accra] => Array
                (
                    [name] => Africa/Accra
                    [offset] => +00:00
                )
                ...
*/