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#include "./period.h"
namespace CppUtilities {
/*!
* \class Period
* \brief Represents a period of time.
*
* In contrast to the TimeSpan class, a Period represents a duration between a concrete
* starting DateTime and end DateTime. Without that context, a Period instance is useless.
*
* Note the absence of the TimeSpan::totalYears() and TimeSpan::totalMonth() methods.
* The reason for this limitation of the TimeSpan class is that the TimeSpan is meant to express
* a duration independently of the concrete starting DateTime and end DateTime.
* However, the concrete calendar interval is neccassary for expressing a duration in terms of years
* and months because not all years and months have the same length.
*
* The Period class, on the other hand, expresses the duration between a *concrete* starting DateTime
* and end DateTime as the number of years, month and days which have been passed **in that particular
* order**. The accuracy is one day, so the DateTime::timeOfDay() is lost.
*
* \remarks The order really matters. For example, the Period between DateTime::fromDateAndTime(1994, 7, 18)
* and DateTime::fromDateAndTime(2017, 12, 2) is 23 years, 4 month and 14 days. That means
* 23 years have been passed, then 4 month and finally 14 days. Adding the 14 days first and then
* the 4 month would make a difference of one day because July has 31 days and November only 30.
*/
/*!
* \brief Constructs a new Period defined by a start DateTime and an end DateTime.
*
* The resulting Period will contain the number of years, month and days which have been passed
* between \a begin and \a end.
*/
Period::Period(DateTime begin, DateTime end)
{
m_years = end.year() - begin.year();
m_months = end.month() - begin.month();
if (m_months < 0) {
m_months += 12;
--m_years;
}
m_days = end.day() - begin.day();
if (m_days < 0) {
m_days += end.month() > 1 ? DateTime::daysInMonth(end.year(), end.month() - 1) : 31;
--m_months;
}
if (m_months < 0) {
m_months += 12;
--m_years;
}
}
/*!
* \brief Adds the specified \a period to the specified date.
* \throws Might throw ConversionException if resulting DateTime would be out-of-range.
* \remarks
* - The order in which the years(), month() and days() are added matters. See the overall class description.
* - Since the accuracy of Period is only one day, the DateTime::timeOfDay() of the result always equals begin.timeOfDay().
*/
DateTime operator+(DateTime begin, Period period)
{
auto year = begin.year() + period.years();
auto month = begin.month() + period.months();
if (month > 12) {
month -= 12;
++year;
}
auto day = begin.day() + period.days();
const auto maxDays = DateTime::daysInMonth(year, month);
if (day > maxDays) {
day -= maxDays;
++month;
}
if (month > 12) {
month -= 12;
++year;
}
return DateTime::fromDate(year, month, day) + begin.timeOfDay();
}
} // namespace CppUtilities
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