Fix TryGet returning false for empty subranges with exclusive parent boundaries (#3)

* Initial plan

* Add test case demonstrating bug with empty subranges in exclusive-start parents

Co-authored-by: blaze6950 <32897401+blaze6950@users.noreply.github.com>

* Fix bug where empty subranges with negative indices returned false instead of empty RangeData

Co-authored-by: blaze6950 <32897401+blaze6950@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: blaze6950 <32897401+blaze6950@users.noreply.github.com>

Author: Copilot

src/Intervals.NET.Data/RangeData.cs

@@ -219,13 +219,6 @@ public bool TryGet(Range<TRangeType> subRange, out RangeData<TRangeType, TDataTy
             endIndex--;
         }
 
-        // Guard against index overflow (long → int cast)
-        if (startIndex < 0 || startIndex > int.MaxValue || endIndex < 0 || endIndex > int.MaxValue)
-        {
-            data = null;
-            return false;
-        }
-
         // Calculate the count of elements to take
         // If adjusted indices result in startIndex > endIndex, the range is empty
         var count = endIndex - startIndex + 1;
@@ -236,6 +229,15 @@ public bool TryGet(Range<TRangeType> subRange, out RangeData<TRangeType, TDataTy
             return true;
         }
 
+        // Guard against index overflow (long → int cast)
+        // Note: We check this after the empty-range handling because a negative endIndex
+        // combined with count <= 0 indicates a logically empty range, not an error
+        if (startIndex < 0 || startIndex > int.MaxValue || endIndex < 0 || endIndex > int.MaxValue)
+        {
+            data = null;
+            return false;
+        }
+
         // Guard against count overflow
         if (count > int.MaxValue)
         {

tests/Intervals.NET.Data.Tests/RangeDataTests.cs

@@ -325,6 +325,62 @@ public void TryGet_SubRange_WithEmptyRange_ReturnsTrueWithEmptyData()
         Assert.Empty(result.Data);
     }
 
+    [Fact]
+    public void TryGet_SubRange_EmptyButContained_WithExclusiveStartParent_ReturnsTrueWithEmptyData()
+    {
+        // Arrange - Parent range: (10,20] means it contains 11, 12, ..., 20
+        var parentRange = Range.OpenClosed<int>(10, 20);
+        var data = new[] { 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 };
+        var rangeData = new RangeData<int, int, IntegerFixedStepDomain>(parentRange, data, _domain);
+
+        // Act - Sub-range (10,10] is logically empty but contained in parent
+        // This tests the fix for the bug where endIndex becomes -1, and the negative-index guard
+        // would return false before the empty-range handling was reached
+        var subRange = Range.OpenClosed<int>(10, 10);
+        var success = rangeData.TryGet(subRange, out var result);
+
+        // Assert - Should return true with empty data, not false
+        Assert.True(success);
+        Assert.NotNull(result);
+        Assert.Empty(result.Data);
+    }
+
+    [Fact]
+    public void TryGet_SubRange_EmptyAtStartBoundary_WithClosedOpenParent_ReturnsTrueWithEmptyData()
+    {
+        // Arrange - Parent range: [10,20) means it contains 10, 11, ..., 19
+        var parentRange = Range.ClosedOpen(10, 20);
+        var data = new[] { 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 };
+        var rangeData = new RangeData<int, int, IntegerFixedStepDomain>(parentRange, data, _domain);
+
+        // Act - Sub-range [10,10) is logically empty
+        var subRange = Range.ClosedOpen(10, 10);
+        var success = rangeData.TryGet(subRange, out var result);
+
+        // Assert - Should return true with empty data
+        Assert.True(success);
+        Assert.NotNull(result);
+        Assert.Empty(result.Data);
+    }
+
+    [Fact]
+    public void TryGet_SubRange_EmptyAtEndBoundary_WithOpenClosedParent_ReturnsTrueWithEmptyData()
+    {
+        // Arrange - Parent range: (10,20] means it contains 11, 12, ..., 20
+        var parentRange = Range.OpenClosed<int>(10, 20);
+        var data = new[] { 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 };
+        var rangeData = new RangeData<int, int, IntegerFixedStepDomain>(parentRange, data, _domain);
+
+        // Act - Sub-range [20,20) is logically empty but at the end boundary
+        var subRange = Range.ClosedOpen(20, 20);
+        var success = rangeData.TryGet(subRange, out var result);
+
+        // Assert - Should return true with empty data
+        Assert.True(success);
+        Assert.NotNull(result);
+        Assert.Empty(result.Data);
+    }
+
     #endregion
 
     #region TryGet Tests - Point