class BaggagePropagator

final class BaggagePropagator implements TextMapPropagatorInterface {
    public const BAGGAGE = 'baggage';
    private static ?self $instance = null;
    public static function getInstance() : self {
        if (null === self::$instance) {
            self::$instance = new self();
        }
        return self::$instance;
    }
    public function fields() : array {
        return [
            self::BAGGAGE,
        ];
    }
    public function inject(&$carrier, ?PropagationSetterInterface $setter = null, ?ContextInterface $context = null) : void {
        $setter ??= ArrayAccessGetterSetter::getInstance();
        $context ??= Context::getCurrent();
        $baggage = Baggage::fromContext($context);
        if ($baggage->isEmpty()) {
            return;
        }
        $headerString = '';
        
        /** @var Entry $entry */
        foreach ($baggage->getAll() as $key => $entry) {
            $value = urlencode((string) $entry->getValue());
            $headerString .= "{$key}={$value}";
            if (($metadata = $entry->getMetadata()
                ->getValue()) !== '' && ($metadata = $entry->getMetadata()
                ->getValue()) !== '0') {
                $headerString .= ";{$metadata}";
            }
            $headerString .= ',';
        }
        if ($headerString !== '' && $headerString !== '0') {
            $headerString = rtrim($headerString, ',');
            $setter->set($carrier, self::BAGGAGE, $headerString);
        }
    }
    public function extract($carrier, ?PropagationGetterInterface $getter = null, ?ContextInterface $context = null) : ContextInterface {
        $getter ??= ArrayAccessGetterSetter::getInstance();
        $context ??= Context::getCurrent();
        if (!($baggageHeader = $getter->get($carrier, self::BAGGAGE))) {
            return $context;
        }
        $baggageBuilder = Baggage::getBuilder();
        $this->extractValue($baggageHeader, $baggageBuilder);
        return $context->withContextValue($baggageBuilder->build());
    }
    private function extractValue(string $baggageHeader, BaggageBuilderInterface $baggageBuilder) : void {
        (new Parser($baggageHeader))->parseInto($baggageBuilder);
    }

}