Bug fix

fix bug: The Recurrence.Weekly enumerator starts with wrong date
#8

Author: Cadabra

src/DateRecurrenceR/Core/WeekDays.cs

@@ -3,7 +3,7 @@ namespace DateRecurrenceR.Core;
 /// <summary>
 /// Represents weekdays for one week.
 /// </summary>
-public struct WeekDays
+public readonly struct WeekDays
 {
 #if NET8_0_OR_GREATER
     private readonly WeekDaysArray _ds;
@@ -98,17 +98,13 @@ public WeekDays(DayOfWeek day1,
         DayOfWeek day6,
         DayOfWeek day7)
     {
-        MinDay = (DayOfWeek) DaysInWeek;
-
         _ds[(int) day1] = true;
         _ds[(int) day2] = true;
         _ds[(int) day3] = true;
         _ds[(int) day4] = true;
         _ds[(int) day5] = true;
         _ds[(int) day6] = true;
         _ds[(int) day7] = true;
-
-        UpdateMinDay();
     }
 
 #if NET8_0_OR_GREATER
@@ -118,11 +114,7 @@ public WeekDays(DayOfWeek day1,
     /// <param name="daysArray"><see cref="WeekDaysArray" /></param>
     public WeekDays(WeekDaysArray daysArray)
     {
-        MinDay = (DayOfWeek) DaysInWeek;
-
         _ds = daysArray;
-
-        UpdateMinDay();
     }
 #endif
 
@@ -144,37 +136,45 @@ public WeekDays(bool isSunday,
         bool isFriday,
         bool isSaturday)
     {
-        MinDay = (DayOfWeek) DaysInWeek;
-
         _ds[0] = isSunday;
         _ds[1] = isMonday;
         _ds[2] = isTuesday;
         _ds[3] = isWednesday;
         _ds[4] = isThursday;
         _ds[5] = isFriday;
         _ds[6] = isSaturday;
-
-        UpdateMinDay();
     }
 
     /// <summary>
     /// Returns a minimal defined day of the week. 
     /// </summary>
-    public DayOfWeek MinDay { get; private set; }
+    public DayOfWeek GetMinByFirstDayOfWeek(DayOfWeek firstDayOfWeek)
+    {
+        var shift = (7 + (int) firstDayOfWeek) % 7;
+        if (_ds[shift]) return (DayOfWeek) shift;
+
+        shift = (7 + (int) firstDayOfWeek + 1) % 7;
+        if (_ds[shift]) return (DayOfWeek) shift;
+
+        shift = (7 + (int) firstDayOfWeek + 2) % 7;
+        if (_ds[shift]) return (DayOfWeek) shift;
+
+        shift = (7 + (int) firstDayOfWeek + 3) % 7;
+        if (_ds[shift]) return (DayOfWeek) shift;
+
+        shift = (7 + (int) firstDayOfWeek + 4) % 7;
+        if (_ds[shift]) return (DayOfWeek) shift;
+
+        shift = (7 + (int) firstDayOfWeek + 5) % 7;
+        if (_ds[shift]) return (DayOfWeek) shift;
+
+        shift = (7 + (int) firstDayOfWeek + 6) % 7;
+        return (DayOfWeek) shift;
+    }
 
     /// <summary>
     /// Returns whether the day of the week has been defined.
     /// </summary>
     /// <param name="dayOfWeek"></param>
     public bool this[DayOfWeek dayOfWeek] => _ds[(int) dayOfWeek];
-
-    private void UpdateMinDay()
-    {
-        for (var i = 0; i < DaysInWeek; i++)
-        {
-            if (!_ds[i]) continue;
-            MinDay = (DayOfWeek) i;
-            break;
-        }
-    }
 }

src/DateRecurrenceR/Helpers/WeeklyRecurrenceHelper.cs

@@ -11,7 +11,7 @@ public static WeeklyHash GetPatternHash(WeekDays weekDays, int interval)
 
         var increment = DaysInWeek * (interval - 1) + 1;
 
-        var weekDayIndex = ((int) weekDays.MinDay + 6) % DaysInWeek;
+        var weekDayIndex = ((int) weekDays.GetMinByFirstDayOfWeek(0) + 6) % DaysInWeek;
 
         for (var i = DaysInWeek; i > 0; i--)
         {
@@ -124,7 +124,8 @@ public static bool TryGetStartDate(DateOnly beginDate,
         int interval,
         out DateOnly startDate)
     {
-        if (!DateHelper.TryGetDateOfDayOfWeek(beginDate, weekDays.MinDay, firstDayOfWeek, out startDate))
+        // if (!DateHelper.TryGetDateOfDayOfWeek(beginDate, weekDays.MinDay, firstDayOfWeek, out startDate))
+        if (!DateHelper.TryGetDateOfDayOfWeek(beginDate, weekDays.GetMinByFirstDayOfWeek(firstDayOfWeek), firstDayOfWeek, out startDate))
         {
             startDate = default;
             return false;

test/DateRecurrenceR.Tests.Unit/Helpers/WeeklyRecurrenceHelperTests.cs

@@ -131,6 +131,31 @@ public void Method_TryGetStartDate_returns_Result_eq_FromDate()
         startDate.Should().Be(fromDate);
     }
 
+    [Fact]
+    public void Method_TryGetStartDate_returns_Result_eq_FromDate_2()
+    {
+        // Arrange
+        var beginDate = new DateOnly(1, 1, 8);
+        var fromDate = beginDate;
+        var firstDayOfWeek = DayOfWeek.Monday;
+        var weekDays = new WeekDays(DayOfWeek.Sunday, DayOfWeek.Monday);
+        var interval = 1;
+        var patternHash = WeeklyRecurrenceHelper.GetPatternHash(weekDays, interval);
+
+        // Act
+        WeeklyRecurrenceHelper.TryGetStartDate(
+            beginDate,
+            fromDate,
+            patternHash,
+            weekDays,
+            firstDayOfWeek,
+            interval,
+            out var startDate);
+
+        //Assert
+        startDate.Should().Be(fromDate);
+    }
+
     [Fact]
     public void Method_GetPatternHash_returns_correct_hash_for_one_day()
     {