package dk.itu.oop.lecture8;

class DateHelper {
	static final int[] daysInMonth={31,28,31,30,31,30,31,31,30,31,30,31,};

	public static class IllegalDateArguments extends IllegalArgumentsException{}
	public static class IllegalDaysAfterArguments extends IllegalDateArguments{
		public final int days;
		public final Date d;
		public IllegalDaysAfterArguments(int days,Date d){
			this.days = d;
			this.d = d;
		}
	}
	public static class IllegalDaysBetweenArguments extends IllegalDateArguments{
		public final Date d1;
		public final Date d2;
		public IllegalDaysBetweenArguments(Date d1,Date d2){
			this.d1 = d1;
			this.d2 = d2;
		}
	}

	public static Date daysAfter(int days, Date d){
		if (days <= 0) throw new IllegalDaysAfterArguments(days, d);
		int day = d.getDay()+days;
		int month = d.getMonth();
		int year = d.getYear();
		while (day > MyDate.daysInMonth[month]){
			days = days - daysInMonth[month];
			month ++;
			if (month>12) {
				year++;
				month = 1;
			}
		}
		return new MyDate(year, month, day);
	}

	public static int daysBetween(Date d1, Date d2){
		int diff = (d2.getYear() - d1.getYear())*365;
		if (diff <= 0 ) throw new IllegalDaysBetweenArguments(d1,d2);
		int dayInYear1 = 0;
		for (int i=1; i<d1.getMonth(); i++)
			// inv: dayInYear1 = sum of the length of all months before month i.
			dayInYear1 += daysInMonth[i-1];
		dayInYear1 += d1.getDay();
		int dayInYear2 = 0;
		for (int i=1; i<d2.getMonth(); i++)
			// inv: dayInYear2 = sum of the length of all months before month i.
			dayInYear2 += daysInMonth[i-1];
		dayInYear2 += d2.getDay();
		diff += (dayInYear2-dayInYear1);
		return diff;
	}
}