Modify some existing implementation of cuisine-customer registration and implement a new function

1. There were few acceptance criteria and I did not violate any ones. 2. I've sent task and I end up did not wait for response (it's been 4 days of a silence). Just after pushing HR in the same day I've received response. 3. in the feedback was said: a) that I'd chosen bad desigh for scalability however without any evidence why. I know companies where suggested solution works successfully (exactly in the same situation!!!!)LOL. b) that I did not handle concurrency - it's truth, I even mentioned this fact in the task and I'd written that it can be refined. Guys, do you think it is possible to write well defined/well-tested/thread-safe design during 2 hours? LOL c) that using enum for some kind of entities like country.. in an app there were just 3 constant string values - is it bad candidate for Enum. I'd adhere to simple and transparent desigh without premature optimisation - becouse it a big evil ))) d) And one of my favorite formulation:"Write up would not work" - what? I've covered my code with Unit tests, and coverage was about 99%, I'd tested every single bit of code - and it will not work? LOL Guys, read please above carefully and make your decision wisely ;)