Example FA

Assumptions

Due to the scope of this quick exercise, the following assumptions are fully aware of but will not be addressed immediately

This library solution only does the shipping cost, otherwise it should be a separate ExampleFA.Shipping assembly in this solution
Only small amount of test cases
- Should only cover some happy paths
- May only has one fail case, per service
The whole process relies on the nullable decimal? data type to respresent the shipping cost, so if this value is null then the shipping has not been calculated.

To get the required outputs, the consumers can
- Call IShippingCostCalculator.ApplyCost on top of the list of items, to calculate their associated cost component
- Then call IShippingCostPrinter.PrintShippingCost to get the total shipping cost, of the above items
For now its all simple/local cost calculations but I make everything async, so it can scale easier i.e. if costs would need to be fetched from remote etc.
I make generic cost calculators, to make it modular i.e. we can just add more cost calculations on top each other.
- Some calculators would depend on other calculators to run before
- For now the calculators run in the order they defined in the list
- Could be nicer to have a way to sort the running order

Probably introduce an Order class, to group the Parcel
Also then we can have a new ICostCalculator<Order, OrderType> implementation
- So that we can apply logic on the whole order as well