Fix issue with Date diff when it includes a daylight time change

src/CalcViewModel/Common/DateCalculator.cpp

@@ -12,6 +12,7 @@ using namespace CalculatorApp::Common::DateCalculation;
 DateCalculationEngine::DateCalculationEngine(_In_ String^ calendarIdentifier)
 {
     m_calendar = ref new Calendar();
+    m_calendar->ChangeTimeZone("UTC");
     m_calendar->ChangeCalendarSystem(calendarIdentifier);
 }
 

src/CalcViewModel/Common/DateCalculator.h

@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
+// Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
 
 #pragma once
@@ -46,7 +46,6 @@ namespace CalculatorApp
                 bool __nothrow AddDuration(_In_ Windows::Foundation::DateTime startDate, _In_ const DateDifference& duration, _Out_ Windows::Foundation::DateTime *endDate);
                 bool __nothrow SubtractDuration(_In_ Windows::Foundation::DateTime startDate, _In_ const DateDifference& duration, _Out_ Windows::Foundation::DateTime *endDate);
                 void __nothrow GetDateDifference(_In_ Windows::Foundation::DateTime date1, _In_ Windows::Foundation::DateTime date2, _In_ DateUnit outputFormat, _Out_ DateDifference *difference);
-
             private:
                 // Private Variables
                 Windows::Globalization::Calendar^ m_calendar;

src/CalcViewModel/DateCalculatorViewModel.cpp

@@ -43,11 +43,7 @@ DateCalculatorViewModel::DateCalculatorViewModel() :
     m_StrDateDiffResultAutomationName(L""),
     m_StrDateDiffResultInDays(L""),
     m_StrDateResult(L""),
-    m_StrDateResultAutomationName(L""),
+    m_StrDateResultAutomationName(L"")
-    m_fromDate({ 0 }),
-    m_toDate({ 0 }),
-    m_startDate({ 0 }),
-    m_dateResult({ 0 })
 {
     const auto& localizationSettings = LocalizationSettings::GetInstance();
 
@@ -56,19 +52,17 @@ DateCalculatorViewModel::DateCalculatorViewModel() :
 
     // Initialize Date Calc engine
     m_dateCalcEngine = make_shared<DateCalculationEngine>(localizationSettings.GetCalendarIdentifier());
-
     // Initialize dates of DatePicker controls to today's date
     auto calendar = ref new Calendar();
+    calendar->ChangeTimeZone("UTC");
     auto today = calendar->GetDateTime();
 
     // FromDate and ToDate should be clipped (adjusted to a consistent hour in UTC)
-    m_fromDate = today;
+    m_fromDate = ClipTime(today);
-    m_toDate = today;
+    m_toDate = ClipTime(today);
-    FromDate = ClipTime(today);
-    ToDate = ClipTime(today);
 
     // StartDate should not be clipped
-    StartDate = today;
+    m_startDate = today;
     m_dateResult = today;
 
     // Initialize the list separator delimiter appended with a space at the end, e.g. ", "
@@ -87,14 +81,14 @@ DateCalculatorViewModel::DateCalculatorViewModel() :
     }
 
     /* In the ClipTime function, we used to change timezone to UTC before clipping the time.
-       The comment from the previous delopers said this was done to eliminate the effects of
+     The comment from the previous delopers said this was done to eliminate the effects of
-       Daylight Savings Time. We can't think of a good reason why this change in timezone is
+     Daylight Savings Time. We can't think of a good reason why this change in timezone is
-       necessary and did find bugs related to the change, therefore, we have removed the
+     necessary and did find bugs related to the change, therefore, we have removed the
-       change. Just in case, we will see if the clipped time is ever a different day from the
+     change. Just in case, we will see if the clipped time is ever a different day from the
-       original day, which would hopefully indicate the change in timezone was actually
+     original day, which would hopefully indicate the change in timezone was actually
-       necessary. We will collect telemetry if we find this case. If we don't see any
+     necessary. We will collect telemetry if we find this case. If we don't see any
-       telemetry events after the application has been used for some time, we will feel safe
+     telemetry events after the application has been used for some time, we will feel safe
-       and can remove this function. */
+     and can remove this function. */
     DayOfWeek trueDayOfWeek = calendar->DayOfWeek;
 
     DateTime clippedTime = ClipTime(today);
@@ -378,13 +372,14 @@ String^ DateCalculatorViewModel::GetLocalizedNumberString(int value) const
     return ref new String(numberStr.c_str());
 }
 
-// Adjusts the given DateTime to 12AM of the same day
+// Adjusts the given DateTime to 12AM (UTC) of the same day 
 DateTime DateCalculatorViewModel::ClipTime(DateTime dateTime)
 {
     auto calendar = ref new Calendar();
+    calendar->ChangeTimeZone("UTC");
     calendar->SetDateTime(dateTime);
-    calendar->Period = 1;
+    calendar->Period = calendar->FirstPeriodInThisDay;
-    calendar->Hour = 12;
+    calendar->Hour = calendar->FirstHourInThisPeriod;
     calendar->Minute = 0;
     calendar->Second = 0;
     calendar->Nanosecond = 0;

src/CalcViewModel/DateCalculatorViewModel.h

@@ -23,7 +23,7 @@ namespace CalculatorApp
             // Input Properties
             OBSERVABLE_PROPERTY_RW(bool, IsDateDiffMode);
             OBSERVABLE_PROPERTY_RW(bool, IsAddMode);
-            OBSERVABLE_PROPERTY_RW(bool, IsDiffInDays);     // If diff is only in days or the dates are the same,
+            OBSERVABLE_PROPERTY_R(bool, IsDiffInDays);     // If diff is only in days or the dates are the same,
                                                             // then show only one result and avoid redundancy
 
             OBSERVABLE_PROPERTY_RW(int, DaysOffset);
@@ -82,11 +82,11 @@ namespace CalculatorApp
             }
 
             // Output Properties
-            OBSERVABLE_PROPERTY_RW(Platform::String^, StrDateDiffResult);
+            OBSERVABLE_PROPERTY_R(Platform::String^, StrDateDiffResult);
-            OBSERVABLE_PROPERTY_RW(Platform::String^, StrDateDiffResultAutomationName);
+            OBSERVABLE_PROPERTY_R(Platform::String^, StrDateDiffResultAutomationName);
-            OBSERVABLE_PROPERTY_RW(Platform::String^, StrDateDiffResultInDays);
+            OBSERVABLE_PROPERTY_R(Platform::String^, StrDateDiffResultInDays);
-            OBSERVABLE_PROPERTY_RW(Platform::String^, StrDateResult);
+            OBSERVABLE_PROPERTY_R(Platform::String^, StrDateResult);
-            OBSERVABLE_PROPERTY_RW(Platform::String^, StrDateResultAutomationName);
+            OBSERVABLE_PROPERTY_R(Platform::String^, StrDateResultAutomationName);
 
             COMMAND_FOR_METHOD(CopyCommand, DateCalculatorViewModel::OnCopyCommand);
 
@@ -104,8 +104,6 @@ namespace CalculatorApp
             Platform::String^ GetLocalizedNumberString(int value) const;
             static Windows::Foundation::DateTime ClipTime(Windows::Foundation::DateTime dateTime);
 
-            static void CheckClipTimeSameDay(Windows::Globalization::Calendar^ reference);
-
             property bool IsOutOfBound
             {
                 bool get() { return m_isOutOfBound; }

src/Calculator/Views/DateCalculator.xaml.cpp

@@ -36,8 +36,6 @@ using namespace Windows::UI::Xaml::Input;
 using namespace Windows::UI::Xaml::Media;
 using namespace Windows::UI::Xaml::Navigation;
 
-// The User Control item template is documented at http://go.microsoft.com/fwlink/?LinkId=234236
-
 DateCalculator::DateCalculator()
 {
     InitializeComponent();