sales_taxes.cpp

#include <iostream>
#include <math.h>
#include <iomanip>
#include <vector>
#include <string>

using namespace std;

class Helper {
private:

public:
	static vector <string> exemptKeywords; 

	static bool isExempt (string name) {
		for (string keyword: exemptKeywords) {
			if (name.find(keyword) != -1)
				return true;
		}
		return false;
	}

	static bool isImported (string name) {
		return name.find("imported") != -1;
	}

	static double rounding (double value) {
		return ceil(value * 20) / 20; // 20 = 1 / 0.05
	}
};

class Good {
private:	
	string name;
	double price;

public:
	int taxRate;

	Good () {}

	Good (string _name, double _price) {
		name = _name;
		price = _price;
		taxRate = 0;

    /* 
      Even though I have made a different design during the interview,
      I realized that splitting goods into 4 different category depending
      whether or not they are exempted or imported is costly and counter-intuitive
      because the tax rate for each case don't have other relation. Hence I only made
      the only class Good instead and sequentially sum up the tax rate depeding on the condition.
    */
		if (!Helper::isExempt(_name)) {
			taxRate += 10;	
		}

		if (Helper::isImported(_name)) {
			taxRate += 5;
		}
	}
	
  // Values are readable, not writable
	string getName () {
		return name;
	}

	double getPrice () {
		return price;
	}
};

class CartGood {
private:
	Good good;
	int amount;

	string getName() {
		return good.getName();
	}
  
  // total = totalPrice + totalTax
	double getTotalPrice () {
		return good.getPrice() * amount;
	}

	double getTotalTax () {
		return Helper::rounding(getTotalPrice() * good.taxRate / 100);
	}

	double getTotal () {
		return getTotalPrice() + getTotalTax();
	}

public:
	CartGood (int _amount, string _name, double _price) {
		amount = _amount;
		good = Good(_name, _price);
	}

  // Only let Cart access the details of each good in cart
	friend class Cart;
};

class Cart {
private:
	vector <CartGood> goods;

	double getTotal () {
		double res = 0;
		for (CartGood g: goods)
			res += g.getTotal();
		return res;
	}

	double getTotalTax () {
		double res = 0;
		for (CartGood g: goods)
			res += g.getTotalTax();
		return Helper::rounding(res);
	}

public:
	void input () {
		int amount;
		string name;
		double price;
		while (true) {
			cout << "Input amount of product (0 to stop): ";
			cin >> amount;
			if (amount == 0)
				break;
			cout << "Input name of product: ";
			cin.ignore();
			getline(cin, name);
			cout << "Input price of product: ";
			cin >> price;
			cout << "Adding product to cart...\n";
			goods.push_back(CartGood(amount, name, price));
		}
	}

	void output () {
		cout << "===RECEIPT===\n";
		for (CartGood g: goods) {
			cout << g.amount << ", " << g.getName() << ", " << fixed << setprecision(2) << g.getTotal() << "\n";
		}
		cout << "Sales Taxes: " << fixed << setprecision(2) << getTotalTax() << "\n";
		cout << "Total: " << fixed << setprecision(2) << getTotal() << "\n";
	}
};


vector <string> Helper::exemptKeywords = {
	"book",
	"chocolate",
	"pill"
	// add more here
};

int main () {
	Cart cart;
	cart.input();
	cart.output();
}