Improve performance by computing room names at sync, rather than on view.

src/Main.elm

@@ -52,6 +52,7 @@ init _ url key =
             , sending = Dict.empty
             , transactionId = 0
             , userData = Dict.empty
+            , roomNames = Dict.empty
             , connected = True
             , searchText = ""
             }
@@ -319,7 +320,7 @@ updateSyncResponse model r notify =
         notificationCmd sr = if notify
             then Maybe.withDefault Cmd.none
                     <| Maybe.map (\(s, e) -> sendNotificationPort
-                    { name = displayName model e.sender
+                    { name = displayName model.userData e.sender
                     , text = notificationText e
                     , room = s
                     }) <| notification sr
@@ -343,9 +344,16 @@ updateSyncResponse model r notify =
             _ -> Cmd.none
         receivedEvents sr = List.map Just <| allTimelineEventIds sr
         sending sr = Dict.filter (\_ (rid, { body, id }) -> not <| List.member id <| receivedEvents sr) model.sending
+        newSync sr = mergeSyncResponse model.sync sr
+        newModel sr =
+            { model | sync = newSync sr
+            , sending = sending (mergeSyncResponse model.sync sr)
+            , roomNames = computeRoomsDisplayNames model.userData (newSync sr)
+            }
     in
         case r of
-            Ok sr -> ({ model | sync = mergeSyncResponse model.sync sr, sending = sending (mergeSyncResponse model.sync sr) }, Cmd.batch
+            Ok sr -> (newModel sr
+                , Cmd.batch
                 [ syncCmd
                 , newUserCmd sr
                 , notificationCmd sr

src/Scylla/Model.elm

@@ -1,6 +1,6 @@
 module Scylla.Model exposing (..)
 import Scylla.Api exposing (..)
-import Scylla.Sync exposing (SyncResponse, HistoryResponse, JoinedRoom, senderName, roomName, roomJoinedUsers)
+import Scylla.Sync exposing (SyncResponse, HistoryResponse, JoinedRoom, senderName, roomName, roomJoinedUsers, findFirst, directMessagesDecoder, AccountData)
 import Scylla.Login exposing (LoginResponse, Username, Password)
 import Scylla.UserData exposing (UserData)
 import Scylla.Route exposing (Route(..), RoomId)
@@ -13,7 +13,7 @@ import Url.Builder
 import Dict exposing (Dict)
 import Time exposing (Posix)
 import File exposing (File)
-import Json.Decode
+import Json.Decode as Decode
 import Browser
 import Http
 import Url exposing (Url)
@@ -31,6 +31,7 @@ type alias Model =
     , sending : Dict Int (RoomId, SendingMessage)
     , transactionId : Int
     , userData : Dict Username UserData
+    , roomNames : Dict RoomId String
     , connected : Bool
     , searchText : String
     }
@@ -54,7 +55,7 @@ type Msg =
     | ReceiveUserData Username (Result Http.Error UserData) -- HTTP, receive user data
     | ReceiveCompletedReadMarker (Result Http.Error ()) -- HTTP, read marker request completed
     | ReceiveCompletedTypingIndicator (Result Http.Error ()) -- HTTP, typing indicator request completed
-    | ReceiveStoreData Json.Decode.Value -- We are send back a value on request from localStorage.
+    | ReceiveStoreData Decode.Value -- We are send back a value on request from localStorage.
     | TypingTick Posix -- Tick for updating the typing status
     | History RoomId -- Load history for a room
     | ReceiveHistoryResponse RoomId (Result Http.Error HistoryResponse) -- HTTP, receive history
@@ -71,27 +72,40 @@ type Msg =
     | AttemptReconnect
     | UpdateSearchText String
 
-displayName : Model -> Username -> String
-displayName m s = Maybe.withDefault (senderName s) <| Maybe.andThen .displayName <| Dict.get s m.userData
+displayName : Dict String UserData -> Username -> String
+displayName ud s = Maybe.withDefault (senderName s) <| Maybe.andThen .displayName <| Dict.get s ud
 
-roomDisplayName : Model -> JoinedRoom -> String
-roomDisplayName m jr =
+roomDisplayName : Model -> RoomId -> String
+roomDisplayName m rid =
+    Maybe.withDefault "<No Name>" <| Dict.get rid m.roomNames
+
+computeRoomDisplayName : Dict String UserData -> Maybe AccountData -> RoomId -> JoinedRoom -> Maybe String
+computeRoomDisplayName ud ad rid jr =
     let
         customName = roomName jr
-        roomUsers = List.filter ((/=) m.loginUsername) <| roomJoinedUsers jr
-        singleUserName = if List.length roomUsers == 1 then List.head roomUsers else Nothing
-        singleUserDisplayName = Maybe.andThen
-            (\u -> Maybe.andThen .displayName <| Dict.get u m.userData) singleUserName
-        firstOption d os = case os of
-            [] -> d
-            ((Just v)::_) -> v
-            (Nothing::xs) -> firstOption d xs
+        direct = ad
+            |> Maybe.andThen .events
+            |> Maybe.andThen (findFirst ((==) "m.direct" << .type_))
+            |> Maybe.map (Decode.decodeValue directMessagesDecoder << .content)
+            |> Maybe.andThen Result.toMaybe
+            |> Maybe.andThen (Dict.get rid)
     in
-        firstOption "<No Name>"
-            [ customName
-            , singleUserDisplayName
-            , singleUserName
-            ]
+        case (customName, direct) of
+            (Just s, _) -> customName
+            (_, Just u) -> direct
+            _ -> Nothing
+
+computeRoomsDisplayNames : Dict String UserData -> SyncResponse -> Dict String String
+computeRoomsDisplayNames ud sr =
+    sr.rooms
+    |> Maybe.andThen .join
+    |> Maybe.map Dict.toList
+    |> Maybe.map (List.foldl
+        (\(rid, jr) d ->
+            computeRoomDisplayName ud sr.accountData rid jr 
+            |> Maybe.map (\n -> Dict.insert rid n d) 
+            |> Maybe.withDefault d) Dict.empty)
+    |> Maybe.withDefault Dict.empty
 
 roomUrl : String -> String
 roomUrl s = Url.Builder.absolute [ "room", s ] []

src/Scylla/Sync.elm

@@ -258,6 +258,22 @@ historyResponseDecoder =
         |> required "end" string
         |> required "chunk" (list roomEventDecoder)
 
+-- Direct Messages
+type alias DirectMessages = Dict String String
+type alias DirectMessagesRaw = Dict String (List String)
+
+directMessagesDecoder : Decoder DirectMessages
+directMessagesDecoder =
+    Decode.dict (Decode.list Decode.string)
+        |> Decode.map (invertDirectMessages)
+
+invertDirectMessages : DirectMessagesRaw -> DirectMessages
+invertDirectMessages dmr =
+    Dict.foldl
+        (\k lv acc -> List.foldl (\v -> Dict.insert v k) acc lv)
+        Dict.empty
+        dmr
+
 -- Business Logic: Helper Functions
 groupBy : (a -> comparable) -> List a -> Dict comparable (List a)
 groupBy f xs =
@@ -268,15 +284,17 @@ groupBy f xs =
     in
         List.foldl (\v acc -> Dict.update (f v) (update v) acc) Dict.empty xs
 
-uniqueByRecursive : (a -> comparable) -> List a -> Set comparable -> List a
-uniqueByRecursive f l s = case l of
-    x::tail -> if Set.member (f x) s
-        then uniqueByRecursive f tail s
-        else x::uniqueByRecursive f tail (Set.insert (f x) s)
-    [] -> []
+uniqueByTailRecursive : (a -> comparable) -> List a -> Set comparable -> List a -> List a
+uniqueByTailRecursive f l s acc =
+    case l of
+        x::tail ->
+            if Set.member (f x) s
+            then uniqueByTailRecursive f tail s acc
+            else uniqueByTailRecursive f tail s (x::acc)
+        [] -> List.reverse acc
 
 uniqueBy : (a -> comparable) -> List a -> List a
-uniqueBy f l = uniqueByRecursive f l Set.empty
+uniqueBy f l = uniqueByTailRecursive f l Set.empty []
 
 findFirst : (a -> Bool) -> List a -> Maybe a
 findFirst cond l = case l of
@@ -302,18 +320,18 @@ findLastEvent = findLastBy .originServerTs
 mergeMaybe : (a -> a -> a) -> Maybe a -> Maybe a -> Maybe a
 mergeMaybe f l r = case (l, r) of
     (Just v1, Just v2) -> Just <| f v1 v2
-    (Just v, Nothing) -> Just v
-    (Nothing, Just v) -> Just v
+    (Just v, Nothing) -> l
+    (Nothing, Just v) -> r
     _ -> Nothing
 
 mergeEvents : List Event -> List Event -> List Event
 mergeEvents l1 l2 = l1 ++ l2
 
 mergeStateEvents : List StateEvent -> List StateEvent -> List StateEvent
-mergeStateEvents l1 l2 = uniqueBy .eventId <| l1 ++ l2
+mergeStateEvents l1 l2 = l1 ++ l2
 
 mergeRoomEvents : List RoomEvent -> List RoomEvent -> List RoomEvent
-mergeRoomEvents l1 l2 = uniqueBy .eventId <| l1 ++ l2
+mergeRoomEvents l1 l2 = l1 ++ l2
 
 mergeStrippedStates : List StrippedState -> List StrippedState -> List StrippedState
 mergeStrippedStates l1 l2 = l1 ++ l2

src/Scylla/Views.elm

@@ -109,18 +109,18 @@ homeserverView m hs rs =
     let
         roomList = div [ class "rooms-list" ]
             <| List.map (\(rid, r) -> roomListElementView m rid r)
-            <| List.sortBy (\(rid, r) -> roomDisplayName m r) rs
+            <| List.sortBy (\(rid, r) -> roomDisplayName m rid) rs
     in
         div [ class "homeserver-wrapper" ] [ h3 [] [ text hs ], roomList ]
 
-roomListElementView : Model -> String -> JoinedRoom -> Html Msg
-roomListElementView m s jr =
+roomListElementView : Model -> RoomId -> JoinedRoom -> Html Msg
+roomListElementView m rid jr =
     let
-        name = roomDisplayName m jr
+        name = roomDisplayName m rid
         isVisible = m.searchText == "" || (String.contains (String.toLower m.searchText) <| String.toLower name)
         isCurrentRoom = case currentRoomId m of
             Nothing -> False
-            Just cr -> cr == s
+            Just cr -> cr == rid
     in
         div [ classList
                 [ ("room-link-wrapper", True)
@@ -129,7 +129,7 @@ roomListElementView m s jr =
                 ]
             ]
             <| roomNotificationCountView jr.unreadNotifications ++
-                [ a [ href <| roomUrl s ] [ text name ] ]
+                [ a [ href <| roomUrl rid ] [ text name ] ]
 
 roomNotificationCountView : Maybe UnreadNotificationCounts -> List (Html Msg)
 roomNotificationCountView ns =
@@ -161,7 +161,7 @@ joinedRoomView m roomId rd =
     let
         renderedMessages = List.map (userMessagesView m) <| mergeMessages m.loginUsername <| extractMessages rd
         messagesWrapper = messagesWrapperView m roomId renderedMessages
-        typing = List.map (displayName m) <| roomTypingUsers rd.joinedRoom
+        typing = List.map (displayName m.userData) <| roomTypingUsers rd.joinedRoom
         typingText = String.join ", " typing
         typingSuffix = case List.length typing of
             0 -> ""
@@ -182,7 +182,7 @@ joinedRoomView m roomId rd =
             ]
     in
         div [ class "room-wrapper" ]
-            [ h2 [] [ text <| roomDisplayName m rd.joinedRoom ]
+            [ h2 [] [ text <| roomDisplayName m roomId ]
             , messagesWrapper
             , messageInput
             , typingWrapper
@@ -215,7 +215,7 @@ messagesWrapperView m rid es = div [ class "messages-wrapper", id "messages-wrap
 
 senderView : Model -> Username -> Html Msg
 senderView m s =
-    span [ style "color" <| stringColor s, class "sender-wrapper" ] [ text <| displayName m s ]
+    span [ style "color" <| stringColor s, class "sender-wrapper" ] [ text <| displayName m.userData s ]
 
 userMessagesView : Model -> (Username, List Message) -> Html Msg
 userMessagesView m (u, ms) =