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Fix #471 (#473)

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[JaEra] Calc: subtracting 1-year from date during Reiwa 1 yields unexpected results.
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Eric Wong 2019-04-24 13:37:49 -07:00 • committed by GitHub
parent b03a026f6c
commit 1dee9dc984
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34
src/CalcViewModel/Common/DateCalculator.cpp
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@ -20,13 +20,27 @@ DateCalculationEngine::DateCalculationEngine(_In_ String^ calendarIdentifier)
// Returns: True if function succeeds to calculate the date else returns False
bool DateCalculationEngine::AddDuration(_In_ DateTime startDate, _In_ const DateDifference& duration, _Out_ DateTime *endDate)
{
auto currentCalendarSystem = m_calendar->GetCalendarSystem();
try
{
m_calendar->SetDateTime(startDate);
if (duration.year != 0)
{
// The Japanese Era system can have multiple year partitions within the same year.
// For example, April 30, 2019 is denoted April 30, Heisei 31; May 1, 2019 is denoted as May 1, Reiwa 1.
// The Calendar treats Heisei 31 and Reiwa 1 as separate years, which results in some unexpected behaviors where subtracting a year from Reiwa 1 results in a date in Heisei 31.
// To provide the expected result across era boundaries, we first convert the Japanese era system to a Gregorian system, do date math, and then convert back to the Japanese era system.
// This works because the Japanese era system maintains the same year/month boundaries and durations as the Gregorian system and is only different in display value.
if (currentCalendarSystem == CalendarIdentifiers::Japanese)
{
m_calendar->ChangeCalendarSystem(CalendarIdentifiers::Gregorian);
}
m_calendar->AddYears(duration.year);
m_calendar->ChangeCalendarSystem(currentCalendarSystem);
}
if (duration.month != 0)
{
@ -41,6 +55,9 @@ bool DateCalculationEngine::AddDuration(_In_ DateTime startDate, _In_ const Date
}
catch (Platform::InvalidArgumentException^ ex)
{
// ensure that we revert to the correct calendar system
m_calendar->ChangeCalendarSystem(currentCalendarSystem);
// Do nothing
return false;
}
@ -52,6 +69,8 @@ bool DateCalculationEngine::AddDuration(_In_ DateTime startDate, _In_ const Date
// Returns: True if function succeeds to calculate the date else returns False
bool DateCalculationEngine::SubtractDuration(_In_ DateTime startDate, _In_ const DateDifference& duration, _Out_ DateTime *endDate)
{
auto currentCalendarSystem = m_calendar->GetCalendarSystem();
// For Subtract the Algorithm is different than Add. Here the smaller units are subtracted first
// and then the larger units.
try
@ -68,13 +87,28 @@ bool DateCalculationEngine::SubtractDuration(_In_ DateTime startDate, _In_ const
}
if (duration.year != 0)
{
// The Japanese Era system can have multiple year partitions within the same year.
// For example, April 30, 2019 is denoted April 30, Heisei 31; May 1, 2019 is denoted as May 1, Reiwa 1.
// The Calendar treats Heisei 31 and Reiwa 1 as separate years, which results in some unexpected behaviors where subtracting a year from Reiwa 1 results in a date in Heisei 31.
// To provide the expected result across era boundaries, we first convert the Japanese era system to a Gregorian system, do date math, and then convert back to the Japanese era system.
// This works because the Japanese era system maintains the same year/month boundaries and durations as the Gregorian system and is only different in display value.
if (currentCalendarSystem == CalendarIdentifiers::Japanese)
{
m_calendar->ChangeCalendarSystem(CalendarIdentifiers::Gregorian);
}
m_calendar->AddYears(-duration.year);
m_calendar->ChangeCalendarSystem(currentCalendarSystem);
}
*endDate = m_calendar->GetDateTime();
}
catch (Platform::InvalidArgumentException^ ex)
{
// ensure that we revert to the correct calendar system
m_calendar->ChangeCalendarSystem(currentCalendarSystem);
// Do nothing
return false;
}