Fix ArgumentOutOfRangeException for extreme datetime

src/Microsoft.Health.Fhir.Core/Features/Search/Expressions/Parsers/SearchValueExpressionBuilderHelper.cs

@@ -100,10 +100,44 @@ void ISearchValueVisitor.Visit(DateTimeSearchValue dateTime)
                     var startTicks = dateTime.Start.UtcTicks;
                     var endTicks = dateTime.End.UtcTicks;
 
-                    var differenceTicks = (long)((Clock.UtcNow.Ticks - Math.Max(startTicks, endTicks)) * ApproximateMultiplier);
-
-                    var approximateStart = dateTime.Start.AddTicks(-differenceTicks);
-                    var approximateEnd = dateTime.End.AddTicks(differenceTicks);
+                    // Calculate the difference safely to avoid overflow
+                    long nowTicks = Clock.UtcNow.Ticks;
+                    long maxTicks = Math.Max(startTicks, endTicks);
+
+                    // Use checked arithmetic to detect overflow, but handle it gracefully
+                    long differenceTicks;
+                    try
+                    {
+                        checked
+                        {
+                            long rawDifference = nowTicks - maxTicks;
+                            differenceTicks = (long)(rawDifference * ApproximateMultiplier);
+                        }
+                    }
+                    catch (OverflowException)
+                    {
+                        // If overflow occurs in calculation, use a safe maximum difference
+                        // This represents approximately 10% of the maximum safe tick range
+                        differenceTicks = long.MaxValue / 20;
+                    }
+
+                    // Ensure we don't overflow when adding/subtracting ticks
+                    long ticksToSubtract = differenceTicks;
+                    long ticksToAdd = differenceTicks;
+
+                    // Clamp to prevent overflow before calling AddTicks
+                    if (startTicks - ticksToSubtract < DateTimeOffset.MinValue.Ticks)
+                    {
+                        ticksToSubtract = startTicks - DateTimeOffset.MinValue.Ticks;
+                    }
+
+                    if (endTicks + ticksToAdd > DateTimeOffset.MaxValue.Ticks)
+                    {
+                        ticksToAdd = DateTimeOffset.MaxValue.Ticks - endTicks;
+                    }
+
+                    DateTimeOffset approximateStart = dateTime.Start.AddTicks(-ticksToSubtract);
+                    DateTimeOffset approximateEnd = dateTime.End.AddTicks(ticksToAdd);
 
                     _outputExpression = Expression.And(
                         Expression.GreaterThanOrEqual(FieldName.DateTimeStart, _componentIndex, approximateStart),

test/Microsoft.Health.Fhir.Shared.Tests.E2E/Rest/Search/DateSearchTests.cs

@@ -236,5 +236,35 @@
                 Assert.Fail($"A non-expected '{e.GetType()}' was raised. Url: {Client.HttpClient.BaseAddress}. No Activity Id present. Error: {e.Message}");
             }
         }
+
+        [Theory]
+        [InlineData("ap9500-01-01")] // Approximate search with future date that causes overflow
+        [InlineData("ap0001-01-01")] // Approximate search with very old date
+        [InlineData("ap9999-12-31")] // Approximate search near max date
+        public async Task GivenAnApproximateDateSearchParamWithExtremeDate_WhenSearched_ThenServerShouldNotCrash(string queryValue)
+        {
+            try
+            {
+                // The server should handle extreme dates gracefully and return a successful response
+                // even if no results are found (empty bundle is OK)
+                Bundle bundle = await Client.SearchAsync(ResourceType.Patient, $"birthdate={queryValue}");
+
+                // If we get here, the server handled it correctly - either with results or an empty bundle
+                Assert.NotNull(bundle);
+                Assert.Equal(Bundle.BundleType.Searchset, bundle.Type);
+            }
+            catch (FhirClientException fce)
+            {
+                // The server should NOT return 500 Internal Server Error for valid approximate date searches
+                // It's acceptable to return BadRequest if the server decides the date is out of reasonable bounds
+                Assert.True(
+                    fce.StatusCode != HttpStatusCode.InternalServerError,
+                    $"Server returned '{HttpStatusCode.InternalServerError}' for a valid approximate date search. This indicates an unhandled exception (overflow) in the date calculation logic. Url: {Client.HttpClient.BaseAddress}. Activity Id: {fce.Response.GetRequestId()}. Error: {fce.Message}");
+            }
+            catch (Exception e)
+            {
+                Assert.Fail($"An unexpected '{e.GetType()}' was raised. The server should handle extreme approximate dates gracefully. Url: {Client.HttpClient.BaseAddress}. Error: {e.Message}");
+            }
+        }
     }
 }