//-------------------------------------------------------------
// Program #5: Calculating Calendars
// 
// Written by: Caitlin Hansen
// November 2008
//
// Purpose: to calculate calendars produced by the user's input
// that includes leap year option, starting days of the week,
// and an entire month of an user designated year.
//-------------------------------------------------------------

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

// ------------------------------------------------------------
// LeapYear determines whether a year is or is not a leap year
// ------------------------------------------------------------
// Accepts:   number representing a year
// Returns:   a true or false calculation
// ------------------------------------------------------------

bool LeapYear ( int year )
{
	int rem;
	rem = year % 4;

	if ( rem == 0 )
		return true;
	else return false;
}

//-------------------------------------------------------------
// DaysInMonth determines the number of days of the month
//-------------------------------------------------------------
// Accepts:  number ( 1 - 12 ) representing month
// Returns:  number of days in that month
//-------------------------------------------------------------

int DaysInMonth ( int monthnum, int year )
{
    int numdays;  // variable for the days in the month

    switch ( monthnum )
    {
        case 1:
        case 3:
        case 5:
        case 7:
        case 8:
        case 10:
        case 12:   numdays = 31;  break;
        case 2:    if ( LeapYear(year) == true )
                      numdays = 29;
                   else
                      numdays = 28;
                   break;
        case 4:
        case 6:
        case 9:
        case 11:   numdays = 30;  break;
    }

return numdays;
}

int CalculateDayofWeek ( int month, int day, int year )
{
	int dayofweek,
	    step1,	// calculates the last two digits of the year
	    step2,	// calculates a quarter of the digits
	    step3,	// calculates the total of the last 2 digits and the quarter
	    code,	// the code for the months
	    last;	// the total of the code, its corresponding int, and the sum of step3

	switch( month )
	{
		case 5:		code = 0; break;
		case 8:		code = 1; break;
		case 2:	
		case 3:	
		case 11:	code = 2; break;
		case 6:		code = 3; break;
		case 9:
		case 12:	code = 4; break;
		case 4:	
		case 7:		code = 5; break;
		case 1:	
		case 10:	code = 6; break;
	}

   step1 = year % 100;
   step2 = step1 / 4;
   step3 = step1 + step2;


	if ( year >= 1700 )
		last = code + step3 + 5;
	else if ( year >= 1800 )
		last = code + step3 + 3;
	else if ( year >= 1900 )
		last = code + step3 + 1;
	else if ( year >= 2100 )
		last = code + step3 + 5;
	else if ( year >= 2200 )
		last = code + step3 + 3;

   dayofweek = ( last + 3 ) % 7;

	if ( LeapYear(year) == true && month == 1 )
		last -= 1;
	else if ( LeapYear(year) == true && month == 2 )
		last -= 1;

return dayofweek;
}


//-------------------------------------------------------------
// DisplayMonthName displays the month name to standard output
//-------------------------------------------------------------
// Accepts:  number ( 1 - 12 ) representing month
// Returns:  nothing
//-------------------------------------------------------------

void DisplayMonthName ( int monthnum )
{
    switch ( monthnum )
    {
        case 1:  cout << "January";  break;
        case 2:  cout << "February";  break;
        case 3:  cout << "March";  break;
        case 4:  cout << "April";  break;
        case 5:  cout << "May";  break;
        case 6:  cout << "June";  break;
        case 7:  cout << "July";  break;
        case 8:  cout << "August";  break;
        case 9:  cout << "September";  break;
        case 10:  cout << "October";  break;
        case 11:  cout << "November";  break;
        case 12:  cout << "December";  break;
    }
}

//-------------------------------------------------------------
// DisplayFirstLine displays the first week in the output
//-------------------------------------------------------------
// Accepts:  number representing days in first week of output
// Returns:  nothing
//-------------------------------------------------------------

void DisplayFirstLine ( int startdayofweek )
{
   int i;
   
   cout << "\n";
   for( i = 0; i < startdayofweek; i ++ )
       cout << "     ";
   for( i = 1; i <= ( 7 - startdayofweek ); i ++ )
       cout << setw(5) << i;
}

//-------------------------------------------------------------
// DisplayFullWeek displays the full week of output
//-------------------------------------------------------------
// Accepts:  number ( resulting start date of week )
// Returns:  nothing
//-------------------------------------------------------------

void DisplayFullWeek ( int startdateofweek )
{
   int i;
   
   cout << "\n";
   for ( i = startdateofweek; i <= ( startdateofweek + 6 ); i ++ )
        cout << setw(5) << i;
}

//-------------------------------------------------------------
// DisplayLastWeek displays the last week of output
//-------------------------------------------------------------
// Accepts:  numbers ( start date of week and number of days in the month )
// Returns:  nothing
//-------------------------------------------------------------

void DisplayLastWeek ( int startdateofweek, int numdaysinmonth )
{
   int i;

   cout << "\n";
   for (i = startdateofweek; i <= numdaysinmonth; i ++)
        cout << setw(5) << i;
}

//-------------------------------------------------------------
// DisplayLastWeek displays the last week of output
//-------------------------------------------------------------
// Accepts:  numbers ( start date of week and number of days in the month )
// Returns:  nothing
//-------------------------------------------------------------

void leapYear( int year )
{
	int startYear, endYear, leapCount = 4;

	startYear = year;
	startYear /= 100;

	switch( startYear )
	{
		case 17:	leapCount = 5; break;
		case 18:	leapCount = 3; break;
		case 19:	leapCount = 1; break;
		case 21:	leapCount = 5; break;
		case 22:	leapCount = 3; break;
	}

}

void DisplayTitleAndHeadings ( int month )
{
	
    cout << endl;
    cout << "\t\t";
    DisplayMonthName ( month );
    cout << endl;
    cout << "   ---------------------------------";
    cout << endl;
    cout << "   Sun  Mon  Tue Wed  Thur Fri  Sat";
    cout << endl;
    cout << "   ---------------------------------";
	
}	
//-------------------------------------------------------------
//  Main Function
//-------------------------------------------------------------

int main ( )
{

// --- Variables

    int monthnum,          // month number ( 1 - 12 ) entered by user
        startdateofweek,   // start date of the week
        begdateofnextweek, // beginning date of the next week
        year,		   // year number ( 1700 - 2299 ) entered by user
        begdayofmonth,     // beginning day of the month
        numdays;           // number of days in month

// --- Validating year amd month numbers

       cout << "\nPlease, Enter the desired year ( 1700-2299 ): ";
       cin >> year;

    while ( year < 1700 || year > 2299 )
    {

       cout << "\n\n!!! Year number must be within the range of 1700 to 2299!!!";
       cout << "\n\nPlease, re-enter year number: ";
       cin >> year;
    }

       cout << "\nPlease, Enter the desired month ( 1 - 12 ): ";
       cin >> monthnum;

    while ( monthnum < 1 || monthnum > 12 )
    {
       cout << "\n\n!!! Month number must be in range 1 - 12 !!!";
       cout << "\n\nPlease re-enter month number: ";
       cin >> monthnum;
    }

// --- Get number of days in month
 
	numdays = DaysInMonth( monthnum, year );
	begdayofmonth = CalculateDayofWeek ( monthnum, 1, year );
	leapYear( year );

// --- Displaying output sentence 

    DisplayTitleAndHeadings ( monthnum );
    DisplayFirstLine( begdayofmonth );
      begdateofnextweek = 8 - begdayofmonth;
    DisplayFullWeek( begdateofnextweek );
      begdateofnextweek += 7;
    DisplayFullWeek( begdateofnextweek );
      begdateofnextweek += 7;
    DisplayFullWeek( begdateofnextweek );
      begdateofnextweek += 7;
  if( numdays - begdateofnextweek >= 7 )
  {
   DisplayFullWeek( begdateofnextweek );
      begdateofnextweek += 7;
  }
    DisplayLastWeek( begdateofnextweek, numdays );
      begdateofnextweek += 7;
    cout << endl;
    cout << endl;

return 0;
}