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Implement the code for a supermarket checkout that calculates the total price of a number of items. In a normal supermarket, things are identified using Stock Keeping Units, or SKUs. In our store, we’ll use individual letters of the alphabet (A, B, C, and so on as the SKUs).
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Our goods are priced individually.
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In addition, some items are multi-priced: buy n of them, and they’ll cost you y.
For example, item ‘A’ might cost 50 pence individually, but this week we have a special offer: buy three ‘A’s and they’ll cost you £1.30.
In fact this week’s prices are:
| Item | Unit Price | Special Price |
|---|---|---|
| A | 50 | 3 for 130 |
| B | 30 | 2 for 45 |
| C | 20 | |
| D | 15 |
- Our checkout accepts items in any order, so that if we scan a B, an A, and another B, we’ll recognise the two B’s and price them at 45 (for a total price so far of 95).
- Because the pricing changes frequently, we need to be able to pass in a set of pricing rules each time we start handling a checkout transaction.