#include <iostream>
#include <iomanip>
#include <string>
#include <fstream>

using namespace std;

//function prototypes
void printmonth(const int, const int);
void printyear(const int);
bool isleap(const int);
int dayofweek(const int, const int, const int);

//global variables
fstream outFile;    //allows user to input/output data to a seperate file
int year;
int startday;
const int DAY_WIDTH = 3;

// *********************************************************************
// * Function Name: main                                               *
// * Description:  This function opens the file for output and prompts *
// *   user to input a year. It then calls function printyear, which   *
// *   uses function printmonth to output the calendar.                *
// *                                                                   *
// * Parameter Description: none                                       *
// *                                                                   *
// * Author: Matthew Draper                                            *
// * Date:  February 3, 2012                                           *
// *********************************************************************
int main()
{
    outFile.open("cal.txt"); // open file
    outFile.seekg(0L, ios::beg); // move read pointer to beg

    cout << "Welcome to the Calendar printing program! \n\n";
    cout << "Please enter a 4 digit year after 1581: ";
    cin >> year;
    cout << endl;

    while (year < 1582 || year > 9999)
    {
        cout << "Invalid. Enter a 4 digit year after 1581: ";
        cin >> year;
        cout << endl;
    }
    //calls printyear function
    printyear(year);

    cout << endl << endl;

    cout << "The Calendar for " << year << " has been sent to and displayed in"
        << " the newly created file." << endl << endl;

    //closes the file
    outFile.close();

    return 0;
}

// *********************************************************************
// * Function Name: isleap                                             *
// * Description:  The function determines if its a leap year          *
// *                                                                   *
// * Parameter Description: int year -> Numeric year                   *
// *                                                                   *
// * Author: Matthew Draper                                            *
// * Date:  February 3, 2012                                           *
// *********************************************************************
bool isleap(const int year)
{
    if (year % 4 == 0)
    {
        if (year % 100 == 0 && year % 400 != 0)
            return false;
        else
            return true;
    }
    else
        return false;
}

// *********************************************************************
// * Function Name: dayofweek                                          *
// * Description:  The function uses the values passed in for the      *
// * starting date, the numeric month, and the user input year.        *
// * year. The day of the week that month started on is then           *
// * calculated and passed back to function 'printmonth'               *
// *                                                                   *
// * Parameter Description: int day -> numeric day of the month        *
// *                        int month -> numeric month of the year     *
// *                        int year ->     numeric year               *
// *                                                                   *
// * Author: Matthew Draper                                            *
// * Date:  February 3, 2012                                           *
// *********************************************************************
int dayofweek(const int day, const int month, const int year)
{
    int a,y,m,d;

    a = (14 - month) / 12;
    y = year - a;
    m = month + (12 * a) - 2;
    d = (day + y + (y / 4) - (y / 100) + (y / 400) + (31 * m / 12)) % 7;
    startday = d;

    return startday;
}

// *********************************************************************
// * Function Name: printmonth                                         *
// * Description:  The function uses the values passed in for the      *
// * the numeric month, and user input year                            *
// * it's a leap year. The month chosen is then printed out correctly. *
// *                                                                   *
// * Parameter Description: int month -> Numeric Month 1-12            *
// *                        int year -> Numeric year                   *
// *                                                                   *
// * Author: Matthew Draper                                            *
// * Date:  February 3, 2012                                           *
// *********************************************************************
void printmonth(const int month, const int year)
{

    int DaysInMonth[13] = {0,31,28,31,30,31,30,31,31,30,31,30,31};
    //calls function isleap and returns true/false
    isleap(year);
    if (isleap(year) == true)
        DaysInMonth[2] = 29;

    string MonthCalled[13]={" ","January", "February", "March", "April", "May",
     "June", "July", "August", "September", "October", "November", "December"};

    string DaysHeader = "Su Mo Tu We Th Fr Sa";
    string centered = MonthCalled[month];

    //this centers the month name over the days and dates
    int chars = centered.length();
    int ws = chars/2 + 10;

    outFile << setw(ws) << MonthCalled[month] << endl;
    outFile << DaysHeader << endl;
    outFile << " ";

    //calls function dayofweek and uses the returned 'startday' value
    dayofweek(1, month, year);

    //loop keeps adding 3 spaces until startday is reached
    for(int i=1; i <= startday; i++)
    {
        outFile << "   ";
    }
    //loop that prints out the date under the corresponding day of week.
    int DayMarker;

    for (int day = 1; day <= DaysInMonth[month]; day++)
    {
        DayMarker = startday + day;

        if (DayMarker % 7 == 0)
            outFile << day << endl << setw(DAY_WIDTH - 1);
        else
            outFile << day << setw(DAY_WIDTH); // correctly formats
    }

    outFile << endl << endl; //creates space between each printed month

    return;
}

// *********************************************************************
// * Function Name: printyear                                          *
// * Description:  This function prints the user requested year and    *
// *     then calls function printmonth 12 times to print the calendar *
// *     for every month of that year.
// * Parameter Description: year - numeric year sent in by user input  *
// *                                                                   *
// * Author: Matthew Draper                                            *
// * Date:  February 3, 2012                                           *
// *********************************************************************
void printyear(const int year)
{
    outFile << setw(12) << year << "\n\n";

    printmonth(1, year);
    printmonth(2, year);
    printmonth(3, year);
    printmonth(4, year);
    printmonth(5, year);
    printmonth(6, year);
    printmonth(7, year);
    printmonth(8, year);
    printmonth(9, year);
    printmonth(10, year);
    printmonth(11, year);
    printmonth(12, year);

    return;
}