This library replicates the basic functions of a Cash Register.

Functionality Includes:

• Adding products to the cash register.
• Calculating a total for all the products.
• Applying a discount coupon to the total.
• Applying special offers when calculating the total (eg. Buy One Get One Free, etc)

Design notes:

• Only one Coupon can be used when calculating the total.
• Only one Offer will be applied to each product.
• Even though the product classses QuantityProduct and WeightProduct exist (to represent items that are purchased individually or items that are weighed before purchase), the cash register simple treats the number of items or weight of items as a quantity as the total price can still be calculated without the cash register being aware of the units of each item. However the two classes provide a starting point for future changes, if, for example, a UI is added and product units become relevant.