// calendar.cpp by mastercomputers
// includes
#include <curses.h>  // contains our console objects
#include <cstdlib>  // contains our string manipulation objects
// classes
class calendar
{
public:
calendar(int d = 1, int m = 1, int y = 2004); // defaults to 1/1/2004 (nz format dd/mm/yy)
virtual ~calendar() {} // does nothing, destructor virtual incase of inheritance
void printcalendar();
private:
bool isleapyear(); // returns true if leap year
int checkday(int); // checks validity of the day
int whatdayisfirstofmonth(); // returns 0 to 6 (Sunday - Saturday)
int howmanydays(); // returns number of days in the month
int day;
int month;
int year;
};
// constructors
calendar::calendar(int d, int m, int y) //checks validity of date and sets the variables
{
if(y < 1582) // Gregorian calendar was accepted 1582
{
 printw("\nThe year %d is before Gregorian Calendar was accepted.\nWill fix to Julian Calendar eventually.\nSetting Year to 1582\nPress ANY key to continue\n", y);
 refresh();
 getch(); // waits for key press
 year = 1582; // invalid year so set to 1582
}
else if(y >= 4904) // Every 3,322 years the calendar is out by a full day
{
 printw("\nEvery 3,322 years would be out by a full day for the Gregorian Calendar.\nI will never live to see if they ever fix it.\nSo I am not correcting this calendar, but do be warned.\nSetting Year to %d\nPress ANY key to continue\n", y, y);
 refresh();
 getch();
 year = y;
}
else
 year = y;  // y is valid so use it to set year
if((m >= 1) && (m <= 12)) // check month between 1 and 12
month = m;  // if it is, sets month
else
{
 printw("\nThe month %d is invalid.  Setting Month to January\nPress ANY key to continue\n", m);
 refresh();
 getch();
 month = 1;
}
day = checkday(d); // validate the day
}

bool calendar::isleapyear()  // checks whether  year is a leap year
{
if((year % 400 == 0) || ((year % 4 == 0) && (year % 100 != 0)))
 return true; // it's a leap year
else
 return false; // it's not a leap year
}

int calendar::checkday(int testday) // checks day is legal for month
{
if((testday > 0) && (testday <= howmanydays()))
 return testday; // day is legal
printw("\nInvalid day entered.  Setting to First of the Month.\nPress ANY key to continue\n");
refresh();
getch();
return 1;  // day is not legal so setting to first day
}

int calendar::howmanydays()
{
if((month == 2) && isleapyear())
 return 29;  // if leap year February has 29 days
static const int daysinmonth[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};  // sets our month days
return daysinmonth[month - 1];
}

int calendar::whatdayisfirstofmonth()  // calculates the day that is first for our month
{
int d = 1; // day is first
int m = month; // the month we selected
int y = year; // the year we selected
int f = (d += m < 3 ? y-- : y - 2, 23 * m / 9 + d + 4 + y / 4 - y / 100 + y / 400) % 7;  // the impressive algorithm to do it
return f; // returns 0-6 (Sunday - Saturday)
}

void calendar::printcalendar() // prints calendar for entered date
{
clear();  // clears the screen
printw("Date entered was >> %d/%d/%d.\n",day, month, year);
printw("\n   SUN    MON    TUE    WED    THU    FRI    SAT\n");
int startday = whatdayisfirstofmonth();
int endday = howmanydays();
for(int i = 0; i < startday; i++)
{
 if(i == 0)
  mvprintw(4, 4, "-");
 if(i == 1)
  mvprintw(4, 11, "-");
 if(i == 2)
  mvprintw(4, 18, "-");
 if(i == 3)
  mvprintw(4, 25, "-");
 if(i == 4)
  mvprintw(4, 32, "-");
 if(i == 5)
  mvprintw(4, 39, "-");
} // end of for loop
int rows = 4;
int count = 1;
for(int j = startday; j < (startday + endday); j++)
{
 if(j % 7 == 0)
 {
  rows += 2;
  move(rows, 4);
 }
 if(j % 7 == 1)
  move(rows, 11);
 if(j % 7 == 2)
  move(rows, 18);
 if(j % 7 == 3)
  move(rows, 25);
 if(j % 7 == 4)
  move(rows, 32);
 if(j % 7 == 5)
  move(rows, 39);
 if(j % 7 == 6)
  move(rows, 46);
 if(count == day)  // set text to red if count is the day entered
 {
  start_color();
  init_pair(COLOR_RED, COLOR_RED, COLOR_BLACK);
  attron(COLOR_PAIR(COLOR_RED));
 }
 printw("%d",count);
 if(count == day) // turns off red text after day has been performed
  attroff(COLOR_PAIR(COLOR_RED));
 count++;
} // end of for loop
printw(" \n\n\n");
refresh();
}

int main(void)
{
initscr(); // starts our console screen buffer
echo();  // allows user input to be seen on screen
raw(); // enables break keys to escape program
if(has_colors() == FALSE) // checks whether console supports color
{
 endwin();
 fprintf(stderr, "Your terminal does not support color\nPress ANY key to exit\n");
 getch();
 return 1;
}
while(true) // indefinite loop
{
 clear(); // clears screen
 printw("Gregorian Calendar.\n\nUse NZ date format: day/month/year.\nUse the ENTER key after each entry.\n\n");
 refresh();
 char input_day[3];
 char input_month[3];
 char input_year[5];
 printw("DAY: ");
 refresh();
 getnstr(input_day, 2); // gets the input as string
 printw("MONTH: ");
 refresh();
 getnstr(input_month, 2);
 printw("YEAR: ");
 refresh();
 getnstr(input_year, 4);
 int d = atoi(input_day);  // converts string to integers(numbers)
 int m = atoi(input_month);
 int y = atoi(input_year);
 calendar date(d, m, y); // instantiates the calendar objects
 date.printcalendar();
 printw("Another calendar (Y/N) ? ");
 refresh();
 char input[2];
 getnstr(input, 1);
 if((input[0] == 'N' || input[0] == 'n'))
  break; // escapes while loop
}
endwin(); // ends out console buffer
return 0;
}