#include <iostream>
#include <cstdlib>
#include <ctime>    //for the functions time and localtime
using namespace std;

class date {
	// Declarations for data members:
	int year;
	int month;  // in the range 1 to 12 inclusive
	int day;    // in the range 1 to 31 inclusive

	static const int length[13]; // Static data member (needs 13 elements)

public:
	// Declarations for member functions:
	date(int m, int d, int y);  // Constructor with 3 arguments
	date();                     // No-argument constructor
	void print() const;         // Const member function
	void next(int n);           // Non-const member function
	void next();
	int dayOfYear() const;      // Returns day number of the year

	// Friend function to calculate distance between two dates
	friend int distance(const date& d1, const date& d2);
};

int main()
{
	try {
		const date independenceDay {7, 4, 1776};   // Month, day, year
		independenceDay.print();
		cout << " is Independence Day.\n";

		// Test the new no-arg constructor
		const date t; // Calls the new constructor
		cout << "Today is ";
		t.print();
		cout << ".\n";

		// Test the dayOfYear function
		const date xmas {12, 25, 2025}; // Call constructor with 3 explicit args.
		cout << "Christmas is day number " << xmas.dayOfYear()
		     << " of the year.\n";    // Make sure it's 359.

		// Test the distance function
		const date summer {6, 20, 2025};  // First day of summer
		const int dist {distance(summer, t)};
		cout << "Only " << dist << " days till summer.\n";
	}
	catch (invalid_argument e) {
		cerr << e.what() << "\n";
		return EXIT_FAILURE;
	}

	return EXIT_SUCCESS;
}

// Initialize static array
const int date::length[] {
	 0,   // Dummy, so that January will have subscript 1
	31,   // January
	28,   // February (ignoring leap years)
	31,   // March
	30,   // April
	31,   // May
	30,   // June
	31,   // July
	31,   // August
	30,   // September
	31,   // October
	30,   // November
	31    // December
};

// Constructor with 3 arguments
date::date(int m, int d, int y) {
	year = y;
	if (m < 1 || m > 12) {
		throw invalid_argument("bad month");
	}
	month = m;

	if (d < 1 || d > length[month]) {
		throw invalid_argument("bad day of the month");
	}
	day = d;
}

// No-argument constructor: Initializes to today's date
date::date() {
	time_t t = time(nullptr);
	tm *p = localtime(&t);
	year = p->tm_year + 1900;
	month = p->tm_mon + 1;
	day = p->tm_mday;
}

// Prints the date in MM/DD/YYYY format
void date::print() const {
	cout << month << "/" << day << "/" << year;
}

// Advances the date by n days
void date::next(int n) {
	for (int i {0}; i < n; ++i) {
		next();
	}
}

// Advances the date by one day
void date::next() {
	if (day < length[month]) {
		++day;
	} else {
		day = 1;  // Advance to the next month
		if (month < 12) {
			++month;
		} else {
			month = 1;  // Advance to the next year
			++year;
		}
	}
}

// Returns the day number of the year (1 to 365)
int date::dayOfYear() const {
	int dayNum = day;
	for (int i = 1; i < month; ++i) {
		dayNum += length[i];
	}
	return dayNum;
}

// Computes the difference in days between two dates
int distance(const date& d1, const date& d2) {
	int yearDiff = d1.year - d2.year;
	int dayDiff = d1.dayOfYear() - d2.dayOfYear();
	return yearDiff * 365 + dayDiff;
}