#include <stdio.h>

enum eDay { //days
    sunday = 1,
    monday,
    tuesday,
    wednesday,
    thursday,
    friday,
    saturday
};
enum eMonth { //months
    january = 1,
    february,
    march,
    april,
    may,
    juny,
    july,
    august,
    september,
    november,
    december
};
int main()
{
    enum eDay day = 0;
    enum eMonth month = 0;
    int firstDayMonth = 0;

    printf("Hello! Welcome to the day calculator!\n");

    while(1) //work till (break;)
    {
        printf("Enter month to check: (1-Jan, 2-Feb, etc) ");
        scanf("%d", &month);

        printf("Enter day to check: ");
        scanf("%d", &day);
        if (checkInput(day, month) == 1)
        {
            do
            {
                printf("Enter the weekday of the 1st of the month: (1-Sunday, 2-Monday, etc) ");
                scanf("%d", &firstDayMonth);

            } while (firstDayMonth < 1 || firstDayMonth > 7);

            switch(dayInWeek(day, month, firstDayMonth)) //for each month - each text
            {
                case sunday:
                    printf("The %02d.%02d will be a Sunday");
                    break;
                case monday:
                    printf("The %02d.%02d will be a Monday");
                    break;
                case tuesday:
                    printf("The %02d.%02d will be a Tuesday");
                    break;
                case wednesday:
                    printf("The %02d.%02d will be a Wednesday");
                    break;
                case thursday:
                    printf("The %02d.%02d will be a Thursday");
                    break;
                case friday:
                    printf("The %02d.%02d will be a Friday");
                    break;
                case saturday:
                    printf("The %02d.%02d will be a Saturday");
                    break;

            }
            break; //all is done, stop program (leave loop)
        }
        else //error in checkInput() method
        {
            printf("Invalid input, try again\n");
        }
    }
}
/*
Calculates the dayName according given DATE (day, month, first day in this month)
input: day, month, first day in the month
output: the dayName in the given month in the given day
*/
int dayInWeek(enum eDay day, enum eMonth month, int firstDayInMonth)
{
    int result = 0;
    result = (firstDayInMonth + --day) % 7;
    if (result == 0)
    {
        result = 7;
    }
    return result;
}
/*
Checks if the day correct according the month (example: in february the day limit is 28)
input: month, day in this month
output: 1 - if valid date, 0 - if invalid
*/
int checkInput(enum eDay d, enum eMonth m)
{
    //check month validity
    if(m >= 1 && m <= 12)
    {
        //check day validity
        if(d >= 1 && d <= 31)
        {
            if((d >= 1 && d <= 30) && (m == 4 || m == 6 || m == 9 || m == 11)) //check for april juny september and november if the date day between 1-30
            {
                return 1;   //valid date
            }
            else if((d >= 1 && d <= 31) && (m == 1 || m ==3 || m == 5 || m == 7 || m == 8 || m == 10 || m == 12)) //check for january, march, may, july, august, october, december if the date day between 1-31
            {
                return 1;   //valid date
            }
            else if((d >= 1 && d <= 28) && (m == 2)) //check for february if the date day between 1-28
            {
                return 1;   //valid date
            }
            else
            {
                return 0;   //invalid day
            }
        }
        else
        {
            return 0;   //day is invalid
        }
    }
    else
    {
        return 0; //month is invalid
    }
}