Public holidays

Hello,
I would like to have special rates for public holidays in my tariffs.
I can think of one way to do this by manually creating tariffs valid on the holidays dates only, but it would be very fastidious.
Is there a smarter way to do that ? I am thinking of overriding the day of week and put sunday in case of a public holiday taken from an external source. Where could I start ?
Thanks
Max

I guess there is a function returning the day of week in the computation of the room price, before retrieving the cost from the complex tariff.
If I override this function and return a sunday in case the day is public holiday, it will use the correct tarriff (ie sunday tariff).

Thanks, I found what I needed in this file and in /administrator/components/com_solidres/models/reservationasset.php

now I would like to have a function isHoliday($date) defined somewhere else, that can be called from those 2 different files.

Where should I define this function?

Thanks
Max