Fixes DateComponents.dayOfWeek fails with arithmetic overflow on …

…Saturdays #4
edjCase · Nov 20, 2023 · 8386b5d · 8386b5d
1 parent 8a51a5c
commit 8386b5d
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Showing 2 changed files with 21 additions and 1 deletion.
diff --git a/internal/Components.mo b/internal/Components.mo
@@ -1010,7 +1010,11 @@ module Module {
         let yearWithoutCentury = year % 100;
         let century = year / 100;
         let h = day + 13 * (month + 1) / 5 + yearWithoutCentury + yearWithoutCentury / 4 + century / 4 + 5 * century;
-        Int.abs(h) % 7 - 1;
+        let position = Int.abs(h) % 7;
+        switch (position) {
+            case (0) 6; // Wrap around -1 (Saturday)
+            case (i) i - 1;
+        };
     };
 
     public func daysInYear(year : Int) : Nat {

diff --git a/test/Components.test.mo b/test/Components.test.mo
@@ -638,6 +638,22 @@ test(
                     dayOfYear = 114;
                 };
             },
+            {
+                components = {
+                    year = 2_023;
+                    month = 11;
+                    day = 18;
+                    hour = 0;
+                    minute = 0;
+                    nanosecond = 0;
+                };
+                expected = {
+                    weekOfYear = 47;
+                    weekYear = 2023;
+                    dayOfWeek = #saturday;
+                    dayOfYear = 322;
+                };
+            },
         ];
         for (testCase in Iter.fromArray(testCases)) {
             let actual : Components.DayOfWeek = Components.dayOfWeek(testCase.components);