From 14cfaaeed5b2feda1abd04a95418f148c86684de Mon Sep 17 00:00:00 2001
From: Sven van Heugten <sven@memcmp.org>
Date: Mon, 5 Jan 2026 21:32:14 +0100
Subject: [PATCH] Generalize the genInteractionListThatEndsAtTime concept

---
 .../ArbitraryInteractionLists.fs              |  8 ++---
 .../InteractionListGenerators.fs              | 32 +++++++++++--------
 NightLight.Core.Tests/NightLightTests.fs      |  4 +--
 3 files changed, 24 insertions(+), 20 deletions(-)

diff --git a/NightLight.Core.Tests/ArbitraryInteractionLists.fs b/NightLight.Core.Tests/ArbitraryInteractionLists.fs
index 9098db1..1a80df4 100644
--- a/NightLight.Core.Tests/ArbitraryInteractionLists.fs
+++ b/NightLight.Core.Tests/ArbitraryInteractionLists.fs
@@ -8,18 +8,18 @@ let private isDay (time: DateTime) =
     time.TimeOfDay >= TimeSpan.FromHours 5.5
     && time.TimeOfDay < TimeSpan.FromHours 20.5
 
-type ArbitraryInteractionsListThatEndsDuringTheDay =
+type ArbitraryInteractionListThatEndsDuringTheDay =
     static member InteractionsList() =
         ArbMap.defaults
         |> ArbMap.generate<DateTime>
         |> Gen.filter isDay
-        |> Gen.bind genInteractionsListThatEndsAtTime
+        |> Gen.bind genInteractionListThatEndsAtTime
         |> Arb.fromGen
 
-type ArbitraryInteractionsListThatEndsDuringTheNight =
+type ArbitraryInteractionListThatEndsDuringTheNight =
     static member InteractionsList() =
         ArbMap.defaults
         |> ArbMap.generate<DateTime>
         |> Gen.filter (not << isDay)
-        |> Gen.bind genInteractionsListThatEndsAtTime
+        |> Gen.bind genInteractionListThatEndsAtTime
         |> Arb.fromGen
diff --git a/NightLight.Core.Tests/InteractionListGenerators.fs b/NightLight.Core.Tests/InteractionListGenerators.fs
index d1e1925..5d620f3 100644
--- a/NightLight.Core.Tests/InteractionListGenerators.fs
+++ b/NightLight.Core.Tests/InteractionListGenerators.fs
@@ -17,25 +17,29 @@ let private genHumanInteraction =
 let private genInteraction =
     Gen.oneof [ genTimeChangedInteraction; genHumanInteraction ]
 
-let private genInteractionsListThatStartsWithTimeChange =
+let private genInteractionsListThatStartsWithTimeChanged =
     gen {
         let! firstInteraction = genTimeChangedInteraction
         let! remainingInteractions = Gen.listOf genInteraction
         return firstInteraction :: remainingInteractions
     }
 
-let private genInteractionsListWhere condition =
-    Gen.listOf (genInteraction |> Gen.filter condition)
+let private genInteractionListContaining containingInteraction afterFilter =
+    gen {
+        let genNonTrivialList =
+            gen {
+                let! before = genInteractionsListThatStartsWithTimeChanged
+                let! after = Gen.listOf (genInteraction |> Gen.filter afterFilter)
+                return before @ containingInteraction :: after
+            }
 
-let genInteractionsListThatEndsAtTime time =
-    let genTrivialList = Gen.constant <| List.singleton (Interaction.TimeChanged time)
+        return!
+            match containingInteraction with
+            | Interaction.TimeChanged _ ->
+                let genTrivialList = Gen.constant <| List.singleton containingInteraction
+                Gen.frequency [ 1, genTrivialList; 9, genNonTrivialList ]
+            | _ -> genNonTrivialList
+    }
 
-    let genNonTrivialList =
-        gen {
-            let! before = genInteractionsListThatStartsWithTimeChange
-            let interactionThatSetsEndTime = Interaction.TimeChanged time
-            let! after = genInteractionsListWhere (not << _.IsTimeChanged)
-            return before @ interactionThatSetsEndTime :: after
-        }
-
-    Gen.frequency [ 1, genTrivialList; 9, genNonTrivialList ]
+let genInteractionListThatEndsAtTime time =
+    genInteractionListContaining (Interaction.TimeChanged time) (not << _.IsTimeChanged)
diff --git a/NightLight.Core.Tests/NightLightTests.fs b/NightLight.Core.Tests/NightLightTests.fs
index 6423a68..a10c86d 100644
--- a/NightLight.Core.Tests/NightLightTests.fs
+++ b/NightLight.Core.Tests/NightLightTests.fs
@@ -21,12 +21,12 @@ type NightLightTests() =
 
         fakeHome
 
-    [<Property(Arbitrary = [| typeof<ArbitraryInteractionsListThatEndsDuringTheDay> |])>]
+    [<Property(Arbitrary = [| typeof<ArbitraryInteractionListThatEndsDuringTheDay> |])>]
     let ``Lights should be white or yellow during the day`` (interactions: Interaction list) =
         let fakeHome = createFakeHomeWithNightLightAndInteract interactions
         fakeHome.ForAllLightsThatAreOn(fun (_, _, color) -> color = White || color = Yellow)
 
-    [<Property(Arbitrary = [| typeof<ArbitraryInteractionsListThatEndsDuringTheNight> |])>]
+    [<Property(Arbitrary = [| typeof<ArbitraryInteractionListThatEndsDuringTheNight> |])>]
     let ``Lights should be red during the night`` (interactions: Interaction list) =
         let fakeHome = createFakeHomeWithNightLightAndInteract interactions
         fakeHome.ForAllLightsThatAreOn(fun (_, _, color) -> color = Red)