You have products database:

1. CEO wants that if you buy at least one tea, next should be free.
2. CTO wants low prices, so that, if you buy 3 or more strawberries price should drop to 4ドル.50.

Your code should be flexible, because CTO and CEO often changes the rules.

The service should look like this:

$ch = new Checkout($pricing_rules);
$co->scan($item1);
$co->scan($item2);
$price = $ch->total();

Implement a checkout system that fulfils these requirements.

Basket: FR1,SR1,FR1,FR1,CF1
Total price expected: 22ドル.45

Basket: FR1,FR1
Total price expected: 3ドル.11

Basket: SR1,SR1,FR1,SR1
Total price expected: 16ドル.61