Handle presence events in Elm

Pass state and diff events to elm, where the state can be managed
accordingly. Because vote events are used to update player state, we
don't want to blindly overwrite it by passing a separately synced
presence list through, as it will lack vote data.

Fixes #1

assets/js/app.js

@@ -38,17 +38,8 @@ app.ports.joinRoom.subscribe(options => {
     let channel = socket.channel("room:" + options.room, {})
 
     // Presence events
-    let presences = {}
-    channel.on("presence_state", state => {
-        console.log("presence state", state)
-        presences = Presence.syncState(presences, state)
-        app.ports.gotPresence.send(presences)
-    })
-    channel.on("presence_diff", diff => {
-        console.log("presence diff", diff)
-        presences = Presence.syncDiff(presences, diff)
-        app.ports.gotPresence.send(presences)
-    })
+    channel.on("presence_state", app.ports.gotPresenceState.send)
+    channel.on("presence_diff", app.ports.gotPresenceDiff.send)
 
     // Incoming room events
     channel.on("vote", app.ports.gotVote.send)

assets/src/PlanningPokerAPI.elm

@@ -1,5 +1,6 @@
 port module PlanningPokerAPI exposing
-    ( gotPresence
+    ( gotPresenceDiff
+    , gotPresenceState
     , gotReset
     , gotReveal
     , gotVote
@@ -73,7 +74,10 @@ encodeAction action =
             wrap "reveal" (Encode.object [])
 
 
-port gotPresence : (Decode.Value -> msg) -> Sub msg
+port gotPresenceState : (Decode.Value -> msg) -> Sub msg
+
+
+port gotPresenceDiff : (Decode.Value -> msg) -> Sub msg
 
 
 port gotVote : (Decode.Value -> msg) -> Sub msg

assets/src/PlanningPokerRoom.elm

@@ -41,12 +41,25 @@ type Msg
     | Reveal
     | PlayerNameChanged String
     | JoinRoom
-    | GotPresence Decode.Value
+    | GotPresence Presence
+    | GotPresenceDiff Decode.Value
     | GotVote Decode.Value
     | GotReveal
     | GotReset
 
 
+type Presence
+    = PresenceState (Dict String Player)
+    | PresenceDiff (Diff (Dict String Player))
+    | PresenceError Decode.Error
+
+
+type alias Diff a =
+    { joins : a
+    , leaves : a
+    }
+
+
 type alias Room =
     { id : String
     , name : String
@@ -138,17 +151,30 @@ update key msg model =
             , API.newProfile { playerName = model.playerName }
             )
 
-        GotPresence value ->
-            case Decode.decodeValue playersDecoder value of
-                Ok players ->
-                    let
-                        newRoom =
-                            { room | players = players }
-                    in
-                    ( { model | room = newRoom }, Cmd.none )
+        GotPresence (PresenceState players) ->
+            let
+                newRoom =
+                    { room | players = players }
+            in
+            ( { model | room = newRoom }, Cmd.none )
 
-                Err _ ->
-                    ( model, Cmd.none )
+        GotPresence (PresenceDiff { joins, leaves }) ->
+            let
+                newPlayers =
+                    room.players
+                        |> Dict.filter (\id _ -> not (Dict.member id leaves))
+                        |> Dict.union joins
+
+                newRoom =
+                    { room | players = newPlayers }
+            in
+            ( { model | room = newRoom }, Cmd.none )
+
+        GotPresence _ ->
+            ( model, Cmd.none )
+
+        GotPresenceDiff _ ->
+            ( model, Cmd.none )
 
         GotVote value ->
             case Decode.decodeValue voteDecoder value of
@@ -194,7 +220,6 @@ view dimensions model =
     let
         device =
             classifyDevice dimensions
-                |> Debug.log "device"
 
         playerName =
             Dict.get model.player model.room.players
@@ -439,13 +464,41 @@ joinForm room playerName =
 subscriptions : Sub Msg
 subscriptions =
     Sub.batch
-        [ API.gotPresence GotPresence
+        [ API.gotPresenceState (decodePresenceState >> GotPresence)
+        , API.gotPresenceDiff (decodePresenceDiff >> GotPresence)
         , API.gotReset (\_ -> GotReset)
         , API.gotReveal (\_ -> GotReveal)
         , API.gotVote GotVote
         ]
 
 
+decodePresenceState : Decode.Value -> Presence
+decodePresenceState value =
+    case Decode.decodeValue playersDecoder value of
+        Ok players ->
+            PresenceState players
+
+        Err error ->
+            PresenceError error
+
+
+decodePresenceDiff : Decode.Value -> Presence
+decodePresenceDiff value =
+    let
+        diffDecoder =
+            Decode.map PresenceDiff <|
+                Decode.map2 Diff
+                    (Decode.field "joins" playersDecoder)
+                    (Decode.field "leaves" playersDecoder)
+    in
+    case Decode.decodeValue diffDecoder value of
+        Ok diff ->
+            diff
+
+        Err error ->
+            PresenceError error
+
+
 playersDecoder : Decode.Decoder (Dict String Player)
 playersDecoder =
     let