From 60bf56fa7bc97f175107018745219fcaef884855 Mon Sep 17 00:00:00 2001
From: konstantin <konstantin.klein@hochfrequenz.de>
Date: Wed, 4 Oct 2023 16:20:38 +0200
Subject: [PATCH] Throw meaningful `ArgumentException` for inconsistent source
 data (#56)

instead of hard to understand exception from base class
---
 .../TimeRangePatchChain.cs                    | 18 +++++++++-
 .../TimeRangePatchChainTests.cs               | 35 +++++++++++++++++++
 2 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/ChronoJsonDiffPatch/ChronoJsonDiffPatch/TimeRangePatchChain.cs b/ChronoJsonDiffPatch/ChronoJsonDiffPatch/TimeRangePatchChain.cs
index d737bcd..4ee4edb 100644
--- a/ChronoJsonDiffPatch/ChronoJsonDiffPatch/TimeRangePatchChain.cs
+++ b/ChronoJsonDiffPatch/ChronoJsonDiffPatch/TimeRangePatchChain.cs
@@ -75,7 +75,23 @@ private static IEnumerable<TimeRangePatch> PrepareForTimePeriodChainConstructor(
             return new List<TimeRangePatch>();
         }
 
-        return timeperiods.OrderBy(tp => tp.Start);
+        var result = timeperiods.OrderBy(tp => tp.Start);
+        var ambigousStarts = result.GroupBy(tp => tp.To).Where(g => g.Count() > 1).Select(g => g.Select(x => x.Start).Distinct());
+        var ambigousEnds = result.GroupBy(tp => tp.End).Where(g => g.Count() > 1).Select(g => g.Select(x => x.End).Distinct()); ;
+        bool baseConstructorIsLikelyToCrash = ambigousStarts.Any() || ambigousEnds.Any();
+        if (baseConstructorIsLikelyToCrash)
+        {
+            try
+            {
+                _ = new TimePeriodChain(result); // a test if the base constructor will actually crash?
+            }
+            catch (InvalidOperationException invalidOpException) when (invalidOpException.Message.EndsWith("out of range"))
+            {
+                // if it would crash and we do know the reasons, then we throw a more meaningful exception here instead of waiting for the base class to crash
+                throw new ArgumentException($"The given periods contain ambiguous starts ({ambigousStarts}) or ends ({ambigousEnds})", innerException: invalidOpException);
+            }
+        }
+        return result;
     }
 
     /// <summary>
diff --git a/ChronoJsonDiffPatch/ChronoJsonDiffPatchTests/TimeRangePatchChainTests.cs b/ChronoJsonDiffPatch/ChronoJsonDiffPatchTests/TimeRangePatchChainTests.cs
index 980662a..f2c52e0 100644
--- a/ChronoJsonDiffPatch/ChronoJsonDiffPatchTests/TimeRangePatchChainTests.cs
+++ b/ChronoJsonDiffPatch/ChronoJsonDiffPatchTests/TimeRangePatchChainTests.cs
@@ -719,4 +719,39 @@ public void Test_Patching_Backwards()
         AssertBasicSanity(myEntity, trpCollection);
         */
     }
+
+    [Fact]
+    public void Test_Patching_Backwards_Throws_Meaningful_Error_For_Inconsistent_Data()
+    {
+        var trpCollection = new TimeRangePatchChain<DummyClass>(patchingDirection: PatchingDirection.ParallelWithTime);
+        var myEntity = new DummyClass
+        {
+            MyProperty = "Foo"
+        };
+        {
+            var keyDate1 = new DateTimeOffset(2034, 1, 1, 0, 0, 0, TimeSpan.Zero);
+            var myChangedEntity = new DummyClass
+            {
+                MyProperty = "Bar"
+            };
+            trpCollection.Add(myEntity, myChangedEntity, keyDate1);
+        }
+        {
+            var keyDate2 = new DateTimeOffset(2035, 1, 1, 0, 0, 0, TimeSpan.Zero);
+            var myChangedEntity = new DummyClass
+            {
+                MyProperty = "Baz"
+            };
+            trpCollection.Add(myEntity, myChangedEntity, keyDate2);
+        }
+        var allPatches = trpCollection.GetAll().ToList();
+        allPatches.Should().HaveCount(3);
+
+        allPatches[1].End = DateTime.MaxValue; // let's a create chain, that is no longer self-consistent and has 2 elements with +infinity as end date
+        allPatches.Where(p => p.End == DateTime.MaxValue).Should().HaveCount(2);
+        Action creatingAChainFromInconsistentPatches = () => new TimeRangePatchChain<DummyClass>(allPatches, PatchingDirection.ParallelWithTime);
+        creatingAChainFromInconsistentPatches.Should().Throw<ArgumentException>()
+            .Where(ae => ae.Message.Contains("The given periods contain ambiguous starts"))
+            .And.InnerException.Should().BeOfType<InvalidOperationException>();
+    }
 }