#ifndef EXERCISE7_11_H_
#define EXERCISE7_11_H_

#include <iostream>
#include <string>

using std::istream;
using std::ostream;
using std::endl;
using std::string;

struct Sales_data {
	string bookNo;
	unsigned units_sold;
	double revenue;

	//constructors
	Sales_data() { units_sold = 0, revenue = 0.0; }
	Sales_data(istream &is);
	Sales_data(string isbn) : bookNo(isbn) {};
	Sales_data(string isbn, unsigned n, double price) : bookNo(isbn), units_sold(n), revenue(n * price) {};

	string isbn() const { return bookNo; }
	double avg_price() const { return revenue / units_sold; }
	Sales_data& combine(Sales_data const &data);		//behave same as the `+=` operator, thus return a left-value
};

//constructors
Sales_data::Sales_data(istream &is){
	double price;
	is >> bookNo >> units_sold >> price;
	revenue = price * units_sold;
}

Sales_data& Sales_data::combine(Sales_data const &data) {
	units_sold += data.units_sold;
	revenue += data.revenue;
	return *this;
}

Sales_data add(Sales_data const &one, Sales_data const &two) {
	Sales_data res = one;
	return res.combine(two);
}

istream& read(istream &is, Sales_data &data) {
	is >> data.bookNo;
	is >> data.units_sold;
	is >> data.revenue;
	return is;
}

ostream& print(ostream &os, Sales_data const data) {
	os << "book number: " << data.bookNo << endl;
	os << "units sold: " << data.units_sold << endl;
	os << "total revenue: " << data.revenue << endl;
	os << "averge price: " << data.avg_price();    // no endl at the end
	return os;
}

#endif