From 2f0540011307e3ea5ae569798c7f7c9b6ff226cb Mon Sep 17 00:00:00 2001
From: Stefan Ceriu <stefanc@matrix.org>
Date: Wed, 23 Aug 2023 19:59:21 +0300
Subject: [PATCH] Dispatch updates to the UI later only after processing all of
 them instead of after each one

---
 .../RoomSummary/RoomSummaryProvider.swift     | 28 +++++++++++--------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/ElementX/Sources/Services/Room/RoomSummary/RoomSummaryProvider.swift b/ElementX/Sources/Services/Room/RoomSummary/RoomSummaryProvider.swift
index de49a5c92..e61b5b7b6 100644
--- a/ElementX/Sources/Services/Room/RoomSummary/RoomSummaryProvider.swift
+++ b/ElementX/Sources/Services/Room/RoomSummary/RoomSummaryProvider.swift
@@ -133,35 +133,41 @@ class RoomSummaryProvider: RoomSummaryProviderProtocol {
         
         MXLog.verbose("\(name): Received \(diffs.count) diffs, current room list \(rooms.compactMap { $0.id ?? "Empty" })")
         
+        var updatedItems = rooms
         for diff in diffs {
-            // Special case resets in order to prevent large updates from blocking the UI
-            // Render the first resetDiffChunkingThreshhold as a reset and then append the rest to give the UI time to update
             let resetDiffChunkingThreshhold = 50
             if case .reset(let values) = diff, values.count > resetDiffChunkingThreshhold {
-                processDiff(RoomListEntriesUpdate.reset(values: Array(values[..<resetDiffChunkingThreshhold])))
-                processDiff(RoomListEntriesUpdate.append(values: Array(values.dropFirst(resetDiffChunkingThreshhold))))
+                // Special case resets in order to prevent large updates from blocking the UI
+                // Render the first resetDiffChunkingThreshhold as a reset and then append the rest to give the UI time to update
+                updatedItems = processDiff(.reset(values: Array(values[..<resetDiffChunkingThreshhold])), on: updatedItems)
+
+                // Once a reset is chunked dispatch the first part to the UI for rendering
+                rooms = updatedItems
+
+                updatedItems = processDiff(.append(values: Array(values.dropFirst(resetDiffChunkingThreshhold))), on: updatedItems)
             } else {
-                processDiff(diff)
+                updatedItems = processDiff(diff, on: updatedItems)
             }
         }
+        rooms = updatedItems
         
         detectDuplicatesInRoomList(rooms)
         
         MXLog.verbose("\(name): Finished applying \(diffs.count) diffs, new room list \(rooms.compactMap { $0.id ?? "Empty" })")
     }
     
-    private func processDiff(_ diff: RoomListEntriesUpdate) {
-        guard let collectionDiff = buildDiff(from: diff, on: rooms) else {
+    private func processDiff(_ diff: RoomListEntriesUpdate, on currentItems: [RoomSummary]) -> [RoomSummary] {
+        guard let collectionDiff = buildDiff(from: diff, on: currentItems) else {
             MXLog.error("\(name): Failed building CollectionDifference from \(diff)")
-            return
+            return currentItems
         }
         
-        guard let updatedItems = rooms.applying(collectionDiff) else {
+        guard let updatedItems = currentItems.applying(collectionDiff) else {
             MXLog.error("\(name): Failed applying diff: \(collectionDiff)")
-            return
+            return currentItems
         }
         
-        rooms = updatedItems
+        return updatedItems
     }
 
     private func fetchRoomInfo(roomListItem: RoomListItemProtocol) -> RoomInfo? {