How to build a Reservation Form with Date validation using Coda Form?

I am trying to build a booking form. It would’ve been ideal if the Date field could recognise already booked dates and do not allow to select it from the calendar - sth like:
image

So, the option is validation of the date field/column. The question is, what would be the validation which checks if the selected Start date in the form is already booked?

It should somehow look at TableBookings, with columns StartDate and EndDate and be false if the date is between any of the periods booked.

Any ideas?

I saw some of your posts @Tomislav_Mamic and @Daniel_Stieber that you were also looking for options for better form validations and I wonder if you have some ideas on my case?