Stop requiring the initial time in NightLightStateMachine

We're only fooling ourselves if we think that it's ready *right* after
construction anyway. After all, the initial state of the lights won't be
updated when the state machine is constructed.

NightLight.Core.Tests/FakeHome.fs

@@ -43,8 +43,8 @@ type FakeLight(light: Light) =
         if hasPower then
             color <- newColor
 
-type FakeHome(now: DateTime) =
-    let mutable nightLightStateMachine = NightLightStateMachine now
+type FakeHome() =
+    let mutable nightLightStateMachine = NightLightStateMachine()
 
     let assertIsOkAndGet result =
         match result with

NightLight.Core.Tests/NightLightTests.fs

@@ -27,22 +27,22 @@ module InteractionsHelpers =
 [<Properties(Arbitrary = [| typeof<Arbitraries> |])>]
 type NightLightTests() =
     [<Property>]
-    let ``Brightness should always be under 255`` (now: DateTime) (interactions: Interaction list) =
-        let fakeHome = FakeHome now
+    let ``Brightness should always be under 255`` (interactions: Interaction list) =
+        let fakeHome = FakeHome()
         fakeHome.Interact interactions
         fakeHome.ForAllLightsThatAreOn(fun (_, brightness, _) -> brightness < 255uy)
 
     [<Property>]
-    let ``Lights should be red during the night`` (now: DateTime) (interactions: Interaction list) =
-        let fakeHome = FakeHome now
+    let ``Lights should be red during the night`` (interactions: Interaction list) =
+        let fakeHome = FakeHome()
         fakeHome.Interact interactions
 
         InteractionsHelpers.isNightAfter interactions
         ==> fakeHome.ForAllLightsThatAreOn(fun (_, _, color) -> color = Red)
 
     [<Property>]
-    let ``Lights should be white or yellow during the day`` (now: DateTime) (interactions: Interaction list) =
-        let fakeHome = FakeHome now
+    let ``Lights should be white or yellow during the day`` (interactions: Interaction list) =
+        let fakeHome = FakeHome()
         fakeHome.Interact interactions
 
         InteractionsHelpers.isDayAfter interactions

NightLight.Core/Models.fs

@@ -17,7 +17,9 @@ type ParseZigbeeEventError =
     | InvalidFriendlyNameField
     | UnknownType
 
-type ParseEventError = ParseZigbeeEventError of ParseZigbeeEventError
+type OnEventReceivedError =
+    | ParseZigbeeEventError of ParseZigbeeEventError
+    | TimeIsUnknown
 
 type Room =
     | Bathroom

NightLight.Core/NightLightStateMachine.fs

@@ -17,13 +17,15 @@ let internal generateZigbeeCommandToFixLight partOfDay light =
 
     generateZigbeeCommand light.FriendlyName color brightness
 
-type NightLightStateMachine(time: DateTime) =
-    member this.OnEventReceived(event: Event) : Result<NightLightStateMachine * Message seq, ParseEventError> =
-        result {
-            let partOfDay = getPartOfDay time
+type NightLightStateMachine private (maybeTime: DateTime option) =
+    new() = NightLightStateMachine None
 
-            match event with
-            | ReceivedZigbeeEvent payload ->
+    member this.OnEventReceived(event: Event) : Result<NightLightStateMachine * Message seq, OnEventReceivedError> =
+        result {
+            let maybePartOfDay = maybeTime |> Option.map getPartOfDay
+
+            match event, maybePartOfDay with
+            | ReceivedZigbeeEvent payload, Some partOfDay ->
                 let! zigbeeEvent = parseZigbeeEvent payload |> Result.mapError ParseZigbeeEventError
 
                 return
@@ -35,14 +37,15 @@ type NightLightStateMachine(time: DateTime) =
                         match maybeLight with
                         | Some light -> generateZigbeeCommandToFixLight partOfDay light |> Seq.singleton
                         | None -> Seq.empty
-            | TimeChanged newTime ->
-                let newState = NightLightStateMachine newTime
+            | TimeChanged newTime, maybePartOfDay ->
+                let newState = NightLightStateMachine(Some newTime)
                 let newPartOfDay = getPartOfDay newTime
 
                 return
                     newState,
-                    if partOfDay <> newPartOfDay then
+                    if maybePartOfDay <> Some newPartOfDay then
                         lights |> Seq.map (generateZigbeeCommandToFixLight newPartOfDay)
                     else
                         Seq.empty
+            | _, None -> return! Error TimeIsUnknown
         }

NightLight/Program.fs

@@ -77,7 +77,14 @@ let mainAsync _ =
         let mqttClientOptions = MqttClientOptionsBuilder().WithTcpServer(server).Build()
 
         let stateLock = new SemaphoreSlim(1, 1)
-        let mutable state = NightLightStateMachine DateTime.Now
+
+        let! initialState =
+            let emptyNightLightStateMachine = NightLightStateMachine()
+
+            TimeChanged DateTime.Now
+            |> handleEvent mqttClient logger emptyNightLightStateMachine
+
+        let mutable state = initialState
 
         mqttClient.add_ApplicationMessageReceivedAsync (fun e ->
             async {