Mono - Reactor, a pozbycie się ifów

 @Override
 @SneakyThrows
    public Publisher<ContainsResult> contains(Path filePath)
    {
        return Mono.fromSupplier(() -> takeFilesByPath(filePath.toString()))
                .filter(files -> !files.isEmpty())
                .map(result -> ContainsResult.FILE_IS_NOT_PRESENT)
                .defaultIfEmpty(ContainsResult.PRESENT)
                .onErrorReturn(ContainsResult.COULD_NOT_CHECK_PRESENCE);
    }

@Override
    public Publisher<PutResult> put(Path filePath, OutputStream outputStream) {
        return Mono.from(contains(filePath))
             ...
    }

PutResult considerContainsResultForPut(ContainsResult containsResult, Path filePath, OutputStream outputStream)
    {
        switch(containsResult)
        {
            case FILE_IS_NOT_PRESENT:
                uploadFile(filePath, outputStream);
                return PutResult.SUCCESS;
            case PRESENT:
                uploadFile(filePath, outputStream);
                return PutResult.FILE_OVERWRITTEN;
            default:
                return PutResult.COULD_NOT_CREATE_FILE;
        }

    }