public function step(ServerRequestInterface $request, ?Tree $tree): ResponseInterface
    {
        $step = $request->getQueryParams()['step'] ?? self::STEP_CHECK;

        switch ($step) {
            case self::STEP_CHECK:
                return $this->wizardStepCheck();

            case self::STEP_PREPARE:
                return $this->wizardStepPrepare();

            case self::STEP_PENDING:
                return $this->wizardStepPending();

            case self::STEP_EXPORT:
                if ($tree === null) {
                    throw new RuntimeException('Exporting a non-existant tree?');
                }

                return $this->wizardStepExport($tree);

            case self::STEP_DOWNLOAD:
                return $this->wizardStepDownload();

            case self::STEP_UNZIP:
                return $this->wizardStepUnzip();

            case self::STEP_COPY:
                return $this->wizardStepCopy();

            case self::STEP_CLEANUP:
                return $this->wizardStepCleanup();
        }

        throw new NotFoundHttpException();
    }