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