#ifndef __DateClass
#define __DateClass

#include <iostream.h>
#include <iomanip.h>

//	The DATE class is designed to represent any date between 1/1/1800
//	and 31/12/2099.  A date is stored numerically as a day of the month,
//	a month of the year, a year number, and the number of days since
//	1/1/1800.

//	The class has two private member functions - for internal use only.

//	setdaynum	Computes the number of days since 1/1/1800.  This
//			function is used only in the constructor to set daynum
//
//	valid		Returns a 1 to indicate a date being constructed is
//			valid (and 0 to indicate an invalid date).  This function
//			is used only in the constructor.  When an error is
//			detected, valid displays an error message.  The arguments
//			are a day number, a month number, and a year number.

//	The class has two constructors.  The default copy constructor and
//	the default destructor are used.
//
//	One constructor takes a day number, a month number, and a year number
//	as arguments and uses them to intialize the date.  The other constructor
//	takes no arguments and initializes the date to the starting date
//	1/1/1800.

//	The class has two named functions, five operator functions, and one
//	friend function.
//
//	weekday		Returns the day number within a week (a number from 0 to 6)
//			where 0 indicates Sunday, 1 Monday, ... and 6 Saturday.
//
//	monthday	Returns the day number within a month.
//
//	operator=	Assigns the rhs date to the lhs date.
//
//	operator-	Returns a day count as the difference between two dates.
//			The argument (the rhs) is a date.
//
//	operator+	Returns a date that is some number of days after the lhs
//			date.  The argument (the rhs) is an int.
//
//	operator==	Returns a 1 if two dates are the same (a 0 otherwise).
//
//	operator<	Returns a 1 if the lhs date is less than (before) the
//			rhs date (a 0 otherwise).
//
//	operator<<	This friend function outputs a date in the form dd mmm yyyy
//			where mmm is a month name abbreviation.
//

class date
{
	private:
		long int 	daynum;          // Number of days since 1/1/1800
		int	 	day;             // Day of month
		int	 	month;           // Month number (1 to 12)
		int	 	year;            // Year (1800 to 2099)

		void 		setdaynum (void);
		int 		valid (int, int, int);

	public:
		date (int, int, int);
		date (void):
			daynum (0), day (1), month (1), year (1800)
			{  }
		int weekday (void)
        		{   return (daynum + 3) % 7; }
		int monthday (void)
        		{   return day; }
		long operator-(const date &rhs)
        		{   return daynum - rhs.daynum; }
		int  operator== (const date &rhs)
        		{   return daynum == rhs.daynum; }
		int  operator< (const date &rhs)
        		{   return daynum < rhs.daynum; }
		date & operator= (const date &);
		date operator+ (int);
		friend ostream & operator<< (ostream &, date &);
};

void date::setdaynum (void)
{
				// setdaynum  computes the daynum for a date

	const int   	monthstart[12] = {0, 31, 59, 90, 120, 151,
				181, 212, 243, 273, 304, 334};
	long 		ycount;
	long		leapdays;

	ycount = year - 1800;
	leapdays = ycount / 4;
	if (((year % 4) == 0) && (month < 3) && (leapdays > 0))
		leapdays--;
	if (leapdays > 24) leapdays--;
	daynum = ycount * 365 + monthstart[month - 1] + leapdays + day - 1;
}

int date::valid (int dd, int mm, int yy)
{
				// valid determines if a date is valid

	const int 	monthsize[12] = {31, 29, 31, 30, 31, 30, 
				31, 31, 30, 31, 30, 31};

	if ((yy < 1800) || (yy > 2099))
	{
		cout << "Invalid year:  " << yy << endl;
		return 0;
    	}
	if ((mm < 1) || (mm > 12))
	{
		cout << "Invalid month:  " << mm << endl;
		return 0;
    	}
	if ((dd < 1) || (dd > monthsize[mm - 1]))
	{
		cout << "Invalid day:  " << dd << endl;
		return 0;
    	}
	if ((dd == 29) && (mm == 2) && (((yy % 4) != 0) ||
		(((yy % 4) == 0) && ((yy % 400) != 0))))
	{
		cout << "Invalid day for non-leap year." << endl;
		return 0;
	}
		return 1;
}

date::date (int dd, int mm, int yy)
{
		// Constructor requiring arguments to build a date
                // Argument order:  day, month, year (4-digits)

    if (!valid (dd, mm, yy))
    {
    	day = 1;
	month = 1;
	year = 1800;
	daynum = 0;
    }
    else
    {
    	day = dd;
	month = mm;
	year = yy;
	setdaynum ();
    }
}

date & date::operator= (const date &rhs)
{
			// Assign one date to another

	if (this != &rhs)     // Prevent useless copy
	{
		day = rhs.day;
		month = rhs.month;
		year = rhs.year;
		daynum = rhs.daynum;
    	}
	return *this;
}

date date::operator+ (int incr)
{
    		// Add some number of days to a date to get another date

	date	temp (*this);
	int	ms[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

	if (incr >= 0)
    	{
		if ((temp.year % 4) == 0) ms[1]++;     // Adjust Feb for leapyear
		if (((temp.year % 100) == 0) && ((temp.year % 400) != 0))
			ms[1]--;
		temp.day += incr;                        // Start by adding to day
    		while (temp.day > ms[temp.month - 1])
		{
			temp.day -= ms[temp.month - 1];
			temp.month++;                    // Advance a month
			if (temp.month > 12)
			{                                // Move to next year
				ms[1] = 28;
				if ((temp.year % 4) == 0) ms[1]++;    // Readjust Feb
				if (((temp.year % 100) == 0) && ((temp.year % 400) != 0))
					ms[1]--;
				temp.year++;             // Advance a year
				temp.month = 1;
			}
		}
		temp.daynum += incr;                     // Update daynum
	}
	else cout << "\n\nInvalid increment in + operation\n";
	return temp;
}

ostream & operator<< (ostream &out, date &dt)
{
    			// Friend to output a date as  dd mmm yyyy

	char	*monthname[12] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun",
					"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};

	out << setw(2) << dt.day;
	out << setw(4) << monthname[dt.month - 1];
	out << setw(5) << dt.year;
	return out;
}
 
#endif