BooleanItemNormalizer.php

<?php

namespace Drupal\test_fieldtype_boolean_emoji_normalizer\Normalizer;

use Drupal\Core\Field\Plugin\Field\FieldType\BooleanItem;
use Drupal\serialization\Normalizer\FieldItemNormalizer;
use Symfony\Component\Serializer\Normalizer\DenormalizerInterface;

/**
 * Normalizes boolean fields weirdly: renders them as 👍 (TRUE) or 👎 (FALSE).
 */
class BooleanItemNormalizer extends FieldItemNormalizer implements DenormalizerInterface {
    
    /**
     * {@inheritdoc}
     */
    protected $supportedInterfaceOrClass = BooleanItem::class;
    
    /**
     * {@inheritdoc}
     */
    public function normalize($object, $format = NULL, array $context = []) {
        $data = parent::normalize($object, $format, $context);
        $data['value'] = $data['value'] ? '👍' : '👎';
        return $data;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function constructValue($data, $context) {
        // Just like \Drupal\serialization\Normalizer\FieldItemNormalizer's logic
        // for denormalization, which uses TypedDataInterface::setValue(), allow the
        // keying by main property name ("value") to be implied.
        if (!is_array($data)) {
            $data = [
                'value' => $data,
            ];
        }
        if (!in_array($data['value'], [
            '👍',
            '👎',
        ], TRUE)) {
            throw new \UnexpectedValueException('Only 👍 and 👎 are acceptable values.');
        }
        $data['value'] = $data['value'] === '👍';
        return $data;
    }

}