Sales_data_ex22.h

#ifndef SALES_DATA_H_
#define SALES_DATA_H_

#include <string>

struct Sales_data;

std::istream &operator>>(std::istream &is, Sales_data &item);
std::ostream &operator<<(std::ostream &os, const Sales_data &item);
Sales_data operator+(const Sales_data &lhs, const Sales_data &rhs);

struct Sales_data
{
friend std::istream& operator>>(std::istream&, Sales_data&);
friend std::ostream& operator<<(std::ostream&, const Sales_data&);
friend Sales_data operator+(const Sales_data&, const Sales_data&);
public:
	Sales_data(const std::string &s, unsigned n, double p) : bookNo(s), units_sold(n), revenue(p*n){std::cout << "Sales_data(const std::string &s, unsigned n, double p)" << std::endl;}
	Sales_data() : Sales_data("", 0, 0){std::cout << "Sales_data() : Sales_data(\"\", 0, 0)" << std::endl;}
	Sales_data(const std::string &s) : Sales_data(s, 0, 0){std::cout << "Sales_data(const std::string &s) : Sales_data" << std::endl;}
	Sales_data(std::istream &is) : Sales_data(){/*read(is, *this);*/ is >> *this; std::cout << "Sales_data(std::istream &is) : Sales_data()" << std::endl;}
	std::string isbn() const {return bookNo;}
	Sales_data& operator=(const std::string&);
    Sales_data& operator+=(const Sales_data&);
    Sales_data& operator-=(const Sales_data&);
private:
	inline double avg_price() const;

    std::string bookNo;
    unsigned units_sold = 0;
    double revenue = 0.0;
};

inline double Sales_data::avg_price() const
{
	if(units_sold)
		return revenue / units_sold;
	else
		return 0;
}

Sales_data& Sales_data::operator=(const std::string &s)
{
	*this = Sales_data(s);
	return *this;
}

Sales_data& Sales_data::operator+=(const Sales_data &rhs)
{
	units_sold += rhs.units_sold;
	revenue += rhs.revenue;

	return *this;
}

Sales_data& Sales_data::operator-=(const Sales_data &rhs)
{
	units_sold -= rhs.units_sold;
	revenue -= rhs.revenue;

	return *this;
}

std::istream &operator>>(std::istream &is, Sales_data &item)
{
	double price = 0;

	is >> item.bookNo >> item.units_sold >> price;
	if(is)
		item.revenue = price * item.units_sold;
	else
		item = Sales_data();

	return is;
}

std::ostream &operator<<(std::ostream &os, const Sales_data &item)
{
	os << item.isbn() << " " << item.units_sold << " " << item.revenue << " " << item.avg_price();

	return os;
}

Sales_data operator+(const Sales_data &lhs, const Sales_data &rhs)
{
	Sales_data sum = lhs;
	sum += rhs;

	return sum;
}

#endif