From 4025bb0b4c846e70c7dbd425981796b49e00c5ee Mon Sep 17 00:00:00 2001
From: Ruben Bartelink <ruben@bartelink.com>
Date: Tue, 18 Feb 2020 08:44:25 +0000
Subject: [PATCH] Complete Process Manager Apply

---
 equinox-fc/Domain/InventoryTransaction.fs | 78 ++++++++++-------------
 1 file changed, 35 insertions(+), 43 deletions(-)

diff --git a/equinox-fc/Domain/InventoryTransaction.fs b/equinox-fc/Domain/InventoryTransaction.fs
index 7d5c4d988..a0088fcab 100644
--- a/equinox-fc/Domain/InventoryTransaction.fs
+++ b/equinox-fc/Domain/InventoryTransaction.fs
@@ -33,7 +33,8 @@ module Events =
         | Added of Added
 
         (* Successful completion *)
-        | Completed // terminal
+        | Logged
+        | Completed
         interface TypeShape.UnionContract.IUnionContract
     let codec = FsCodec.NewtonsoftJson.Codec.Create<Event>()
 
@@ -42,6 +43,7 @@ module Fold =
     type State =
         | Initial
         | Running of RunningState
+        | Logging of TerminalState
         | Completed of TerminalState
     and RunningState =
         | Adjust of Events.AdjustmentRequested
@@ -61,10 +63,10 @@ module Fold =
     let evolve state event =
         match state, event with
         (* Adjustment Process *)
-        | Initial, Events.AdjustmentRequested e ->
-            Running (Adjust e)
-        | Running (Adjust s), Events.Adjusted ->
-            Completed (Adjusted s)
+        | Initial, Events.AdjustmentRequested r ->
+            Running (Adjust r)
+        | Running (Adjust r), Events.Adjusted ->
+            Logging (Adjusted r)
 
         (* Transfer Process *)
         | Initial, Events.TransferRequested e ->
@@ -73,57 +75,47 @@ module Fold =
         | Running (Transfer (Requested s)), Events.Failed ->
             Completed (TransferFailed s)
 
-        | Running (Transfer (Requested s)), Events.Removed e as ee ->
+        | Running (Transfer (Requested s)), Events.Removed e ->
             Running (Transfer (Adding { request = s; removed = e }))
-        | Running (Transfer (Adding s)), Events.Added e as ee ->
+        | Running (Transfer (Adding s)), Events.Added e ->
             Running (Transfer (Added { request = s.request; removed = s.removed; added = e  }))
-        | Running (Transfer (Added s)), Events.Completed as ee ->
-            Completed (Transferred s)
+        | Running (Transfer (Added s)), Events.Completed ->
+            Logging (Transferred s)
+
+        (* Log result *)
+        | Logging s, Events.Logged ->
+            Completed s
 
         (* Any disallowed state changes represent gaps in the model, so we fail fast *)
         | state, event -> failwithf "Unexpected %A when %A" event state
     let fold : State -> Events.Event seq -> State = Seq.fold evolve
 
-type Command =
-    | Adjust of Events.AdjustmentRequested
-    | Transfer of Events.TransferRequested
-
-type Result = { complete : bool;  }
-
-/// Holds events accumulated from a series of decisions while also evolving the presented `state` to reflect the pended events
-type private Accumulator() =
-    let acc = ResizeArray()
-    member __.Ingest(state) : 'res * Events.Event list -> 'res * Fold.State = function
-        | res, [] ->                   res, state
-        | res, [e] -> acc.Add e;       res, Fold.evolve state e
-        | res, xs ->  acc.AddRange xs; res, Fold.fold state (Seq.ofList xs)
-    member __.Accumulated = List.ofSeq acc
-
-type Update =
-    | AdjustmentCompleted
-
-let decide command updates (state : Fold.State) : Result * Events.Event list =
-
-    let acc = Accumulator()
-    let started, state =
-        acc.Ingest state <|
-            match state, command with
-            | Fold.Initial, Adjust e -> true, [ Events.AdjustmentRequested e ]
-            | Fold.Initial, Transfer e -> true, [ Events.TransferRequested e ]
-
-            // TOCONSIDER validate conflicts
-
-            | _ -> false, []
-
-    { complete = false }, acc.Accumulated
+    /// Validates an event actually represents an acceptable, non-redundant state transition
+    let filter event state =
+        match state, event with
+        | Initial,                          Events.AdjustmentRequested _
+        | Initial,                          Events.TransferRequested _
+        | Running (Adjust _),               Events.Adjusted
+        | Running (Transfer (Requested _)), Events.Failed
+        | Running (Transfer (Requested _)), Events.Removed _
+        | Running (Transfer (Adding _)),    Events.Added _
+        | Logging _,                        Events.Logged ->
+            [event]
+        | _ -> []
+
+/// Given an event from the Process's timeline, yields the State, in order that it can be completed
+let decide update (state : Fold.State) : Fold.State * Events.Event list =
+    let events = Fold.filter update state
+    let state' = Fold.fold state events
+    state', events
 
 type Service internal (log, resolve, maxAttempts) =
 
     let resolve (Events.For streamId) = Equinox.Stream<Events.Event, Fold.State>(log, resolve streamId, maxAttempts)
 
-    member __.IngestShipped(inventoryId, transactionId, command, updates) : Async<Result> =
+    member __.Apply(transactionId, update) : Async<Fold.State> =
         let stream = resolve transactionId
-        stream.Transact(decide command updates)
+        stream.Transact(decide update)
 
 let createService resolve = Service(Serilog.Log.ForContext<Service>(), resolve, maxAttempts = 2)