#include <iostream>
#include <cstdlib>
#include "coffee.h"
using namespace std;

coffee::coffee(int init_mg)
	: mg {init_mg}
{
	if (mg < 0) {
		cerr << "Bad caffeine amount " << init_mg << "\n";
		exit(EXIT_FAILURE);
	}
}

coffee::coffee()
	: mg {100}   //default cup has 100 mg remaining
{
}

coffee& coffee::operator+=(int n)
{
	mg += n;
	if (mg < 0) {   //if someone added a negative number too large
		mg = 0;
	}
	return *this;
}

coffee& coffee::operator-=(int n)
{
	mg -= n;
	if (mg < 0) {
		mg = 0;
	}
	return *this;
}

coffee& coffee::operator++()      //prefix
{
	*this += 1;
	return *this;
}

const coffee coffee::operator++(int)  //postfix
{
	coffee old {*this};  //copy
	++(*this);           //call prefix
	return old;
}

coffee& coffee::operator--()      //prefix
{
	*this -= 1;
	return *this;
}

const coffee coffee::operator--(int)  //postfix
{
	coffee old {*this};
	--(*this);
	return old;
}

ostream& operator<<(ostream& os, const coffee& c)
{
	return os << c.mg << "mg";
}

int operator-(const coffee& a, const coffee& b)
{
	return a.mg - b.mg;
}

bool operator==(const coffee& a, const coffee& b)
{
	return a.mg == b.mg;
}

bool operator<(const coffee& a, const coffee& b)
{
	return a.mg < b.mg;
}