#include <iostream>  //for cout
#include "date.h"
using namespace std; //because invalid_argument and cout belong to namespace std

const int date::length[] {
	 0,   //dummy, so that January will have subscript 1
	31,   //January
	28,   //February.  Pretend there are no leap years.
	31,   //March
	30,   //April
	31,   //May
	30,   //June
	31,   //July
	31,   //August
	30,   //September
	31,   //October
	30,   //November
	31    //December
};

//The constructor installs 2 valid values into a newborn date object,
//or it throws an exception.

date::date(int m, int d, int y)
        : year {y}, day {d}
{
	if (m < 1 || m > 12) {
		throw invalid_argument("bad month");
	}
	if (d < 1 || d > length[m]) {
		throw invalid_argument("bad day of the month");
	}

	//Add to day the sum of all the days in all the months before month m.
	for (int month {1}; month < m; ++month) {
		day += length[month];
	}
}

void date::print() const
{
	int d {day};      //d is probably too big
	int m {1};

	for (; d > length[m]; ++m) {   //Cut d down to size.
		d -= length[m];
	}

	cout << m << "/" << d << "/" << year;
}

void date::next(int n)   //Can change the date struct.
{
	for (int i {0}; i < n; ++i) {
		next(); //Call the other next function, the one with no argument
	}
}

void date::next()          //Move this date one day into the future.
{
	if (day < 365) {
		++day;
	} else {
		day = 1;   //Advance into the next year.
		++year;
	}
}

void date::prev(int n)
{
	for (int i {0}; i < n; ++i) {
		prev();
	}
}

void date::prev()            //Move this date one day into the past.
{
	if (day > 1) {
		--day;
	} else {
		day = 365;   //Retreat into the previous year.
		--year;
	}
}