Date difference: display the difference in days (only) when we aren't able to calculate the difference in days/weeks/months.. (#555)

* Display date difference in days if can't display in days/weeks/months/...

* add comments

* remove not used variable totalDaysDiff

* improve UpdateDisplayResult

* Display error message when the calculator can't calculate the difference between 2 dates

src/CalcViewModel/Common/DateCalculator.cpp

@@ -119,7 +119,7 @@ bool DateCalculationEngine::SubtractDuration(_In_ DateTime startDate, _In_ const
 }
 
 // Calculate the difference between two dates
-void DateCalculationEngine::GetDateDifference(_In_ DateTime date1, _In_ DateTime date2, _In_ DateUnit outputFormat, _Out_ DateDifference* difference)
+bool DateCalculationEngine::TryGetDateDifference(_In_ DateTime date1, _In_ DateTime date2, _In_ DateUnit outputFormat, _Out_ DateDifference* difference)
 {
     DateTime startDate;
     DateTime endDate;
@@ -176,8 +176,9 @@ void DateCalculationEngine::GetDateDifference(_In_ DateTime date1, _In_ DateTime
                         catch (Platform::InvalidArgumentException ^)
                         {
                             // Operation failed due to out of bound result
-                            // Do nothing
+                            // For example: 31st Dec, 9999 - last valid date
-                            differenceInDates[unitIndex] = 0;
+                            *difference = DateDifferenceUnknown;
+                            return false;
                         }
                     }
 
@@ -190,6 +191,12 @@ void DateCalculationEngine::GetDateDifference(_In_ DateTime date1, _In_ DateTime
                         if (tempDaysDiff < 0)
                         {
                             // pivotDate has gone over the end date; start from the beginning of this unit
+                            if (differenceInDates[unitIndex] == 0)
+                            {
+                                // differenceInDates[unitIndex] is unsigned, the value can't be negative
+                                *difference = DateDifferenceUnknown;
+                                return false;
+                            }
                             differenceInDates[unitIndex] -= 1;
                             pivotDate = tempPivotDate;
                             pivotDate = AdjustCalendarDate(pivotDate, dateUnit, static_cast<int>(differenceInDates[unitIndex]));
@@ -211,16 +218,25 @@ void DateCalculationEngine::GetDateDifference(_In_ DateTime date1, _In_ DateTime
                             }
                             catch (Platform::InvalidArgumentException ^)
                             {
-                                // handling for 31st Dec, 9999 last valid date
+                                // Operation failed due to out of bound result
-                                // Do nothing - break out
+                                // For example: 31st Dec, 9999 - last valid date
-                                break;
+                                *difference = DateDifferenceUnknown;
+                                return false;
                             }
                         }
                     } while (tempDaysDiff != 0); // dates are the same - exit the loop
 
                     tempPivotDate = AdjustCalendarDate(tempPivotDate, dateUnit, static_cast<int>(differenceInDates[unitIndex]));
                     pivotDate = tempPivotDate;
-                    daysDiff = GetDifferenceInDays(pivotDate, endDate);
+                    int signedDaysDiff = GetDifferenceInDays(pivotDate, endDate);
+                    if (signedDaysDiff < 0)
+                    {
+                        // daysDiff is unsigned, the value can't be negative
+                        *difference = DateDifferenceUnknown;
+                        return false;
+                    }
+
+                    daysDiff = signedDaysDiff;
                 }
             }
         }
@@ -232,6 +248,7 @@ void DateCalculationEngine::GetDateDifference(_In_ DateTime date1, _In_ DateTime
     difference->month = differenceInDates[1];
     difference->week = differenceInDates[2];
     difference->day = differenceInDates[3];
+    return true;
 }
 
 // Private Methods

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
@@ -35,8 +35,15 @@ namespace CalculatorApp
                 int month = 0;
                 int week = 0;
                 int day = 0;
+
+                bool operator==(const DateDifference& dd) const
+                {
+                    return year == dd.year && month == dd.month && week == dd.week && day == day;
+                }
             };
 
+            const DateDifference DateDifferenceUnknown{ INT_MIN, INT_MIN, INT_MIN, INT_MIN };
+
             class DateCalculationEngine
             {
             public:
@@ -50,7 +57,7 @@ namespace CalculatorApp
                     _In_ Windows::Foundation::DateTime startDate,
                     _In_ const DateDifference& duration,
                     _Out_ Windows::Foundation::DateTime* endDate);
-                void __nothrow GetDateDifference(
+                bool __nothrow TryGetDateDifference(
                     _In_ Windows::Foundation::DateTime date1,
                     _In_ Windows::Foundation::DateTime date2,
                     _In_ DateUnit outputFormat,

src/CalcViewModel/DateCalculatorViewModel.cpp

@@ -122,11 +122,24 @@ void DateCalculatorViewModel::OnInputsChanged()
         DateTime clippedToDate = ClipTime(ToDate, true);
 
         // Calculate difference between two dates
-        m_dateCalcEngine->GetDateDifference(clippedFromDate, clippedToDate, m_allDateUnitsOutputFormat, &dateDiff);
+        if (m_dateCalcEngine->TryGetDateDifference(clippedFromDate, clippedToDate, m_daysOutputFormat, &dateDiff))
-        DateDiffResult = dateDiff;
+        {
-
+            DateDiffResultInDays = dateDiff;
-        m_dateCalcEngine->GetDateDifference(clippedFromDate, clippedToDate, m_daysOutputFormat, &dateDiff);
+            if (m_dateCalcEngine->TryGetDateDifference(clippedFromDate, clippedToDate, m_allDateUnitsOutputFormat, &dateDiff))
-        DateDiffResultInDays = dateDiff;
+            {
+                DateDiffResult = dateDiff;
+            }
+            else
+            {
+                // TryGetDateDifference wasn't able to calculate the difference in days/weeks/months/years, we will instead display the difference in days.
+                DateDiffResult = DateDiffResultInDays;
+            }
+        }
+        else
+        {
+            DateDiffResult = DateDifferenceUnknown;
+            DateDiffResultInDays = DateDifferenceUnknown;
+        }
     }
     else
     {
@@ -158,14 +171,21 @@ void DateCalculatorViewModel::UpdateDisplayResult()
 {
     if (m_IsDateDiffMode)
     {
-        // Are to and from dates the same
+        if (m_dateDiffResultInDays == DateDifferenceUnknown)
-        if (m_dateDiffResultInDays.day == 0)
         {
+            IsDiffInDays = false;
+            StrDateDiffResultInDays = L"";
+            StrDateDiffResult = AppResourceProvider::GetInstance().GetResourceString(L"CalculationFailed");
+        }
+        else if (m_dateDiffResultInDays.day == 0)
+        {
+            // to and from dates the same
             IsDiffInDays = true;
             StrDateDiffResultInDays = L"";
             StrDateDiffResult = AppResourceProvider::GetInstance().GetResourceString(L"Date_SameDates");
         }
-        else if ((m_dateDiffResult.year == 0) && (m_dateDiffResult.month == 0) && (m_dateDiffResult.week == 0))
+        else if (m_dateDiffResult == DateDifferenceUnknown ||
+            (m_dateDiffResult.year == 0 && m_dateDiffResult.month == 0 && m_dateDiffResult.week == 0))
         {
             IsDiffInDays = true;
             StrDateDiffResultInDays = L"";

src/Calculator/Resources/en-US/Resources.resw

@@ -3399,4 +3399,8 @@
     <value>Scroll Calculation Result Right</value>
     <comment>Automation label for the "Scroll Right" button that appears when a calculation result is too large to fit in calculation result text box.</comment>
   </data>
-</root>
+  <data name="CalculationFailed" xml:space="preserve">
+    <value>Calculation failed</value>
+    <comment>Text displayed when the application is not able to do a calculation</comment>
+  </data>
+</root>

src/CalculatorUnitTests/DateCalculatorUnitTests.cpp

@@ -300,7 +300,7 @@ TEST_METHOD(TestDateDiff)
     //    }
 
     //    // Calculate the difference
-    //    m_DateCalcEngine.GetDateDifference(DateUtils::SystemTimeToDateTime(datetimeDifftest[testIndex].startDate),
+    //    m_DateCalcEngine.TryGetDateDifference(DateUtils::SystemTimeToDateTime(datetimeDifftest[testIndex].startDate),
     //    DateUtils::SystemTimeToDateTime(datetimeDifftest[testIndex].endDate), dateOutputFormat, &diff);
 
     //    // Assert for the result
@@ -1050,8 +1050,7 @@ TEST_METHOD(JaEraTransitionDifference)
     auto endTime = cal->GetDateTime();
 
     DateDifference diff;
-    viewModel->GetDateDifference(startTime, endTime, DateUnit::Day, &diff);
+    VERIFY_IS_TRUE(viewModel->TryGetDateDifference(startTime, endTime, DateUnit::Day, &diff));
-
     VERIFY_ARE_EQUAL(diff.day, 19);
 }
 }