class Protocols

class Protocols {
    public const GRPC = KnownValues::VALUE_GRPC;
    public const HTTP_PROTOBUF = KnownValues::VALUE_HTTP_PROTOBUF;
    public const HTTP_JSON = KnownValues::VALUE_HTTP_JSON;
    public const HTTP_NDJSON = KnownValues::VALUE_HTTP_NDJSON;
    private const PROTOCOLS = [
        self::GRPC => ContentTypes::PROTOBUF,
        self::HTTP_PROTOBUF => ContentTypes::PROTOBUF,
        self::HTTP_JSON => ContentTypes::JSON,
        self::HTTP_NDJSON => ContentTypes::NDJSON,
    ];
    public static function validate(string $protocol) : void {
        if (!array_key_exists($protocol, self::PROTOCOLS)) {
            throw new UnexpectedValueException('Unknown protocol: ' . $protocol);
        }
    }
    
    /**
     * @psalm-return ContentTypes::*
     */
    public static function contentType(string $protocol) : string {
        self::validate($protocol);
        return self::PROTOCOLS[$protocol];
    }

}