//JulianDate.java     102a
//calculate julian date of any year/month/day input.
//a program with lots of if statements.

import javax.swing.*;

public class JulianDate extends JApplet {

    public void init () {

	String input;
	int year, month, day;
	int previousMonthDays;
	String leap;
	int julian;
	
	input = JOptionPane.showInputDialog(null,"Enter year");
	year = Integer.parseInt(input);
	if (year < 1753) {
	    JOptionPane.showMessageDialog(null,"Sorry, calendar was wacky before 1753.  Bye!");
	    return;
	}
	
	input = JOptionPane.showInputDialog(null,"Enter month number");
	month = Integer.parseInt(input);
	if (month<1 || month>12) {
	    JOptionPane.showMessageDialog(null,"bogus month.  Bye!");
	    return;
	}
	
	input = JOptionPane.showInputDialog(null,"Enter day");
	day = Integer.parseInt(input);
	if (day<1 || day>31) {
	    JOptionPane.showMessageDialog(null,"bogus day.  Bye!");
	    return;
	}
	
	//test for leapyear.
	//a year is a leap year if evenly divisible by 4 but not also evenly
	//divisible by 100 unless also evenly divisible by 400.
	//I.e. century years are not normally leap years unless they are also 400
	//years.  1800, 1900, 2100 are not leap years, but 2000 is.
	if (year%4==0 && year%100!=0 || year%400==0)
	    leap = "yes";
	else
	    leap = "no";
	
	//test that month day combo is valid.  have already checked that day is <= 31
	//So know that 31 day months are valid.
	if (month==4 || month==6 || month==9 || month==11) {  //30 day months
	    if (day > 30) {
		if (month == 4)
		    JOptionPane.showMessageDialog(null,"April has only 30 days.  Bye!");
		else if (month == 6)
		    JOptionPane.showMessageDialog(null,"June has only 30 days.  Bye!");
		else if (month == 4)
		    JOptionPane.showMessageDialog(null,"September has only 30 days.  Bye!");
		else if (month == 11)
		    JOptionPane.showMessageDialog(null,"November has only 30 days.  Bye!");
		return;
	    }
	}
	else
	    if (month == 2)   //Feb.
		if (leap.equals("no")) {   //not a leap year
		    if (day > 28) {
			JOptionPane.showMessageDialog(null,"February has only 28 days this year.  Bye!");
			return;
		    }
		}
		else    //is leap year
		    if (day > 29) {
			JOptionPane.showMessageDialog(null,"February has only 29 days this year.  Bye!");
			return;
		    }
	
	//determine the number of days in all the previous months
	previousMonthDays = 0;
	if (month > 1)
	    previousMonthDays += 31;   //Jan
	if (month > 2) {
	    previousMonthDays += 28;   //Feb
	    if (leap.equals("yes"))
		previousMonthDays++;     //Feb 29
	}
	if (month > 3)
	    previousMonthDays += 31;   //Mar
	if (month > 4)
	    previousMonthDays += 30;   //Apr
	if (month > 5)
	    previousMonthDays += 31;   //May
	if (month > 6)
	    previousMonthDays += 30;   //Jun
	if (month > 7)
	    previousMonthDays += 31;   //Jul
	if (month > 8)
	    previousMonthDays += 31;   //Aug
	if (month > 9)
	    previousMonthDays += 30;   //Sep
	if (month > 10)
	    previousMonthDays += 31;   //Oct
	if (month > 11)
	    previousMonthDays += 30;   //Nov
	
	julian = previousMonthDays + day;

	JOptionPane.showMessageDialog(null,"Julian date: " + julian);
    }
}