Add Custom Order Attributes

namespace App\Transformers;

use League\Fractal\TransformerAbstract;
use Illuminate\Support\Collection;

class CustomAttributeTransformer extends TransformerAbstract
{
    protected $availableIncludes = [];
    protected $defaultIncludes = [];

    public function __construct($signsField, $jsonSignsField = null)
    {
        $this->signsField = $signsField;
        $this->jsonSignsField = $jsonSignsField;
    }

    public function transform(Collection $collection)
    {
        // Initialize array for additional information.
        $additionalInformation = [];

        // Source - this comes from values sent to this transformer.
        foreach ($collection->{$this->signsField} ?: [] as $value) {
            if (is_array($value)) {
                // If value is an array, serialize it.
                foreach ($value as &$item) {
                    if (isset($item['custom_attr'])) {
                        // Serialize custom attribute data.
                        ...
                    }
                }
            } else {
                // Add non-array values directly.
                ...
            }
        }

        ...

        return [
            'current' => ...,
            'additional_information' => ...,
            'source' => ...,
        ];
    }

    private function flatten(array $values)
    {
      return Arr::flatten($values);
  }
}

namespace Magento\AepCustomAttributes\Model\Provider;

use Magento\Framework\Serialize\Serializer\Json;

class OrderItemCustomAttribute
{
    private Json $jsonSerializer;
    private string $usingField;

    public function __construct(Json $jsonSerializer, string $usingField)
    {
        $this->jsonSerializer = $jsonSerializer;
        $this->usingField = $usingField;
    }

    public function get(array $values): array
    {
        $output = [];
        $values = $this->flatten($values);

        foreach ($values as $row) {
            $info = \is_string($row['additionalInformation']) ? $row['additionalInformation'] : '{}';
            $unserializedData = $this->jsonSerializer->unserialize($info) ?? [];

            $attrLabel = implode(',', ['label1', 'label2']);
            $unserializedData['custom_attr1'] = $attrLabel;

            $additionalInformation = [];
            foreach ($unserializedData as $name => $value) {
                $additionalInformation[] = [
                    'name' => $name,
                    'value' => \is_string($value) ? $value : $this->jsonSerializer->serialize($value),
                ];
            }

            foreach ($additionalInformation as $information) {
                $output[] = [
                    'additionalInformation' => $information,
                    $this->usingField => $row[$this->usingField],
                ];
            }
        }

        return $output;
    }

    private function flatten(array $values): array
    {
        return array_merge([], ...array_values($values));
    }
}

namespace Magento\Catalog\Model\Product;

use Magento\Framework\App\ResourceConnection;
use Magento\Quote\Api\Data\CartInterface;

class ProductContext
{
    private $brandCache = [];
    private $resourceConnection;

    public function __construct(
        ResourceConnection $resourceConnection
    ) {
        $this->resourceConnection = $resourceConnection;
    }

    public function afterGetProductData($subject, array $result)
    {
        if (isset($result['brand_id'])) {
            if (!isset($this->brandCache[$result['brand_id']])) {
                // @todo load brand label by brand id.
                $this->brandCache[$result['brand_id']] = 'Brand Label ' . $result['brand_id'];
            }
            $result['brands'] = ['label' => $this->brandCache[$result['brand_id']]];
        }

        return $result;
    }
}

use \Magento\Framework\Component\ComponentRegistrar;

ComponentRegistrar::register(
    ComponentRegistrar::MODULE,
    'Dfe_Stripe',
    __DIR__
);