SwiftUI timeline refactor + TimelineViewState decoupling (#1392)

* swiftUI conversion + scroll to bottom

* remove unused

* back pagination implemented, however when a lot of elements are in the scroll the perfomance diminishes not sure what may be causing it

* scroll adapter solution

* way better

* works but height animation in cells are broken

* code improvement

* everything implemented

* rebase fix

* fix

* doc

* fix test compilation

* code improvement and animation improvement

* code improvement

* code improvements

* tests updated.

* pr comments

* better identifiers

* fix

* some PR comments

* pr comments

ElementX/Sources/Screens/RoomScreen/RoomScreenModels.swift

@@ -51,7 +51,6 @@ enum RoomScreenComposerMode: Equatable {
 
 enum RoomScreenViewAction {
     case displayRoomDetails
-    case paginateBackwards
     case itemAppeared(itemID: TimelineItemIdentifier)
     case itemDisappeared(itemID: TimelineItemIdentifier)
     case itemTapped(itemID: TimelineItemIdentifier)
@@ -86,18 +85,14 @@ struct RoomScreenViewState: BindableState {
     var roomId: String
     var roomTitle = ""
     var roomAvatarURL: URL?
-    var itemsDictionary = OrderedDictionary<String, RoomTimelineItemViewModel>()
     var members: [String: RoomMemberState] = [:]
-    var canBackPaginate = true
-    var isBackPaginating = false
     var showLoading = false
     var timelineStyle: TimelineStyle
     var readReceiptsEnabled: Bool
     var isEncryptedOneToOneRoom = false
-    
+    var timelineViewState = TimelineViewState() // check the doc before changing this
     var composerMode: RoomScreenComposerMode = .default
-    let scrollToBottomPublisher = PassthroughSubject<Void, Never>()
-    
+
     var bindings: RoomScreenViewStateBindings
     
     /// A closure providing the actions to show when long pressing on an item in the timeline.
@@ -106,14 +101,6 @@ struct RoomScreenViewState: BindableState {
     var sendButtonDisabled: Bool {
         bindings.composerText.count == 0
     }
-
-    var timelineIDs: [String] {
-        itemsDictionary.keys.elements
-    }
-
-    var itemViewModels: [RoomTimelineItemViewModel] {
-        itemsDictionary.values.elements
-    }
 }
 
 struct RoomScreenViewStateBindings {
@@ -184,3 +171,21 @@ struct RoomMemberState {
     let displayName: String?
     let avatarURL: URL?
 }
+
+/// Used as the state for the TimelineView, to avoid having the context continuously refresh the list of items on each small change.
+/// Is also nice to have this as a wrapper for any state that is directly connected to the timeline.
+struct TimelineViewState {
+    var canBackPaginate = true
+    var isBackPaginating = false
+    var itemsDictionary = OrderedDictionary<String, RoomTimelineItemViewState>()
+
+    var timelineIDs: [String] {
+        itemsDictionary.keys.elements
+    }
+
+    var itemViewStates: [RoomTimelineItemViewState] {
+        itemsDictionary.values.elements
+    }
+
+    var paginateAction: (() -> Void)?
+}