Present sales by date and calculate totals.
Make Sale class.
Move reporting to Reports::SalesByDate class.
Report sales by country.
Report sales by shop.
Automatically load all report classes.
Make csv-parsing a method.
Autoload using require_relative instead.
Autoinvoke render method for all reports loaded.
Instantiate reports instead of using static methods.
Refactor code, use blocks instead of returning arrays.
Reports pick up their data from the row rather than the sale object.