A Symfony Form extension to display emoji country flag for CountryType

CountryTypeExtension.php

<?php

declare(strict_types=1);

namespace App\Form\Extension;

use Symfony\Component\Form\AbstractTypeExtension;
use Symfony\Component\Form\ChoiceList\ChoiceList;
use Symfony\Component\Form\ChoiceList\Loader\IntlCallbackChoiceLoader;
use Symfony\Component\Form\Exception\LogicException;
use Symfony\Component\Form\Extension\Core\Type\CountryType;
use Symfony\Component\Intl\Countries;
use Symfony\Component\Intl\Intl;
use Symfony\Component\OptionsResolver\Options;
use Symfony\Component\OptionsResolver\OptionsResolver;

final class CountryTypeExtension extends AbstractTypeExtension
{
    public const FORMAT_WITH_NAME = '{name}';
    public const FORMAT_WITH_FLAG = '{flag}';
    public const FORMAT_WITH_FLAG_AND_NAME = '{flag} {name}';

    public const FLAG_POSITION_BEFORE = 'before';
    public const FLAG_POSITION_AFTER = 'after';

    public static function getExtendedTypes(): iterable
    {
        return [CountryType::class];
    }

    public static function getFlag(string $countryCode): string
    {
        $offset = 0x1F1A5;

        return
            mb_chr($offset + mb_ord($countryCode[0], 'UTF-8'), 'UTF-8').
            mb_chr($offset + mb_ord($countryCode[1], 'UTF-8'), 'UTF-8');
    }

    public function configureOptions(OptionsResolver $resolver): void
    {
        $resolver->setDefaults([
            'choice_loader' => function (Options $options) {
                if (!class_exists(Intl::class)) {
                    throw new LogicException(sprintf('The "symfony/intl" component is required to use "%s". Try running "composer require symfony/intl".', CountryType::class));
                }

                $choiceTranslationLocale = $options['choice_translation_locale'];
                $alpha3 = $options['alpha3'];
                $format = $options['format'];
                $flagPosition = $options['flag_position'];

                return ChoiceList::loader($this, new IntlCallbackChoiceLoader(function () use ($choiceTranslationLocale, $alpha3, $format, $flagPosition) {
                    $countries = $alpha3 ? Countries::getAlpha3Names($choiceTranslationLocale) : Countries::getNames($choiceTranslationLocale);

                    $choices = $countries;

                    if (self::FORMAT_WITH_FLAG === $format) {
                        foreach ($countries as $countryCode => $countryName) {
                            $choices[$countryCode] = self::getFlag($countryCode);
                        }
                    } elseif (self::FORMAT_WITH_FLAG_AND_NAME === $format) {
                        $choices = [];

                        foreach ($countries as $countryCode => $countryName) {
                            $values = [self::getFlag($countryCode), $countryName];

                            if (self::FLAG_POSITION_AFTER === $flagPosition) {
                                $values = array_reverse($values);
                            }

                            $choices[$countryCode] = sprintf('%s %s', ...$values);
                        }
                    }

                    return array_flip($choices);
                }), [$choiceTranslationLocale, $alpha3]);
            },
            'format' => self::FORMAT_WITH_NAME,
            'flag_position' => self::FLAG_POSITION_BEFORE,
        ]);

        $resolver->setAllowedTypes('format', ['string']);
        $resolver->setAllowedTypes('flag_position', ['string']);

        $resolver->setAllowedValues('format', [self::FORMAT_WITH_NAME, self::FORMAT_WITH_FLAG, self::FORMAT_WITH_FLAG_AND_NAME]);
        $resolver->setAllowedValues('flag_position', [self::FLAG_POSITION_BEFORE, self::FLAG_POSITION_AFTER]);
    }
}