The application uses local time to calculate the number of days between 2 dates. If a Daylight Saving Time takes place during this period of time (only Clocks Forward 2am->3am), the application will miss 1 day and fail to calculate the number of days/weeks/months between the 2 dates.
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Description of the changes:
DateCalculationEngine uses local time to modify dates, however, AddDays, AddWeeks,... won't add 24 hours or 7 days if DST happens between the 2 dates, but instead add ~23.9/24.1 hours or ~6.9/7.1 days (depends if it's the DST clock backward or clock forward). When the DST is clock forward, DateCalculationEngine will miss one day.
Solution
use UTC dates to calculate date difference.
Extra Fix:
use calendar->FirstPeriodInThisDay and calendar->FirstHourInThisPeriod in ClipTime (else it will set the time to 12PM (noon) in some regions.
replace OBSERVABLE_PROPERTY_RW by OBSERVABLE_PROPERTY_R when possible.
remove the definition of CheckClipTimeSameDay (implementation missing)
How changes were validated:
Tested manually with different regions (FR, US, ES, JP).
Fixes#178
Optimize how we build the result of GetDateDiffString and GetDateDiffStringInDays, using std::wstring (mutuable) instead of Platform::String (immutable)
