// difference *this - OtherDate
unsigned long Date::Difference(Date &OtherDate, TimeUnit Unit, bool RoundUp) const {
unsigned long Result = 0;
switch (Unit) {
case YEAR:
Result = Data[YEAR] - OtherDate.Data[YEAR];
break;
case MONTH:
Result = (Data[YEAR] - OtherDate.Data[YEAR])*12 + Data[MONTH] - OtherDate.Data[MONTH];
break;
case DAY:
if (OtherDate.Data[YEAR] == Data[YEAR]) {
if (OtherDate.Data[MONTH] == Data[MONTH]) {
Result = Data[DAY] - OtherDate.Data[DAY];
} else {
Result = (OtherDate.DaysInMonth() - OtherDate.Data[DAY]) + Data[DAY];
for (char i=OtherDate.Data[MONTH]+1; i<Data[MONTH]; ++i)
Result += OtherDate.DaysInMonth(i);
}
} else {
// number of days in the starting year
Result = OtherDate.DaysInMonth() - OtherDate.Data[DAY];
for (char i=OtherDate.Data[MONTH]+1; i<=12; ++i)
Result += OtherDate.DaysInMonth(i);
// number of days in years between the starting and ending years
for (short i=OtherDate.Data[YEAR]+1; i<Data[YEAR]; ++i)
Result += IsLeapYear(i) ? 366 : 365;
// number of days in the ending year
for (char i=1; i<Data[MONTH]; ++i)
Result += DaysInMonth(i);
Result += Data[DAY];
}
break;
case HOUR:
if (Data[DAY] == OtherDate.Data[DAY]) {
Result = Data[HOUR] - OtherDate.Data[HOUR];
} else {
Result = 24 - OtherDate.Data[HOUR];
Result += (Difference(OtherDate, DAY, false) - 1) * 24;
Result += Data[HOUR];
}
break;
case MINUTE:
if (Data[HOUR] == OtherDate.Data[HOUR]) {
Result = Data[MINUTE] - OtherDate.Data[MINUTE];
} else {
Result = 60 - OtherDate.Data[MINUTE];
Result += (Difference(OtherDate, HOUR, false) - 1) * 60;
Result += Data[MINUTE];
}
break;
case SECOND:
if (Data[MINUTE] == OtherDate.Data[MINUTE]) {
Result = Data[SECOND] - OtherDate.Data[SECOND];
} else {
Result = 60 - OtherDate.Data[SECOND];
Result += (Difference(OtherDate, MINUTE, false) - 1) * 60;
Result += Data[SECOND];
}
break;
case WEEK:
Result = Difference(OtherDate, DAY, false)/7 + 1;
break;
}
if (RoundUp == true && Unit < SECOND && Compare(OtherDate, (TimeUnit)(Unit+1)) > 0)
++Result;
return Result;
}
