How do I design a Strategy Pattern Class in C++ based on an UML Diagram? - c++

Question

I'm designing a strategy pattern based on the following diagram:
I have to base the entire program on two things: the contents of the main function, and the Sale function getTotal() - which I was provided with;
Here's what I managed to write so far:
class Product {
private:
int code;
string type;
string description;
int price;
public:
Product(int code, string type, string description, int price): code{code}, type{type}, description{description}, price{price}{}
int getPrice() {
return price;
}
};
class SaleItem {
private:
Product product;
public:
int quantity;
Product getProduct() {
return product;
}
int getQuantity() {
return quantity;
}
};
class Sale {
public:
SaleItem s;
Sale(SaleItem s) : s{ s }{}
vector<SaleItem> items;
void additem(int n, Product p) {
items.push_back(s(n,p));
}
double getTotal();
};
class DiscountPolicy {
public:
virtual double getDiscount(const Sale* s, SaleItem si) = 0;
};
class CreditCardDiscount : public DiscountPolicy {
public:
virtual double getDiscount(const Sale* s, SaleItem si) {
return si.getQuantity() * si.getProduct().getPrice() * 0.02;
}
};
class NoDiscount : public DiscountPolicy {
public:
virtual double getDiscount(const Sale* s, SaleItem si) {
return si.getQuantity() * si.getProduct().getPrice() * 0.00;
}
};
double Sale::getTotal() {
double total = 0;
for (int i = 0; i < items.size(); i++) {
SaleItem sIt = items[i];
double price = sIt.getQuantity() * sIt.getProduct().getPrice();
//apply discount
price -= discountPolicy->getDiscount(this, sIt);
total += price;
}
return total;
}
int main() {
Sale s(new NoDiscount());
Product p1(1, "Apple", "food", 2.0);
Product p2(1, "TV", "electronics", 2000.0);
s.addItem(3, p1);
s.addItem(1, p2);
assert(s.getTotal() == 2006);
Sale s2(new CreditCardDiscount());
s2.addItem(3, p1);
s2.addItem(1, p2);
//total with discount for card
assert(s2.getTotal() == 1965.88);
}
I'm currently encountering two issues:
I can't wrap my head around designing the Sale class so that "Sale s(new NoDiscount());" and " Sale s2(new CreditCardDiscount());", from the main class, make sense.
I'm fairly certain there should be some code where the //apply discount comment is found in the getTotal() function, but I'm not sure how to implement it so that "price -= discountPolicy->getDiscount(this, sIt);" works.
The rest of the program should be implemented correctly, since I've seen similar designs, it's mainly the Sale function that I don't understand.
Appreciate the help!