From 55cbbc54978ae778bee3ec564df7153210ae4e14 Mon Sep 17 00:00:00 2001
From: Stefan Ceriu <stefanc@matrix.org>
Date: Tue, 22 Aug 2023 15:23:28 +0300
Subject: [PATCH] Split incoming large .resets into a reset + append in order
 to quicker update the UI

---
 .../RoomSummary/RoomSummaryProvider.swift     | 37 ++++++++++++-------
 1 file changed, 24 insertions(+), 13 deletions(-)

diff --git a/ElementX/Sources/Services/Room/RoomSummary/RoomSummaryProvider.swift b/ElementX/Sources/Services/Room/RoomSummary/RoomSummaryProvider.swift
index 749c3eb67..6e439a898 100644
--- a/ElementX/Sources/Services/Room/RoomSummary/RoomSummaryProvider.swift
+++ b/ElementX/Sources/Services/Room/RoomSummary/RoomSummaryProvider.swift
@@ -133,25 +133,36 @@ class RoomSummaryProvider: RoomSummaryProviderProtocol {
         
         MXLog.info("\(name): Received \(diffs.count) diffs, current room list \(rooms.compactMap { $0.id ?? "Empty" })")
         
-        rooms = diffs
-            .reduce(rooms) { currentItems, diff in
-                guard let collectionDiff = buildDiff(from: diff, on: currentItems) else {
-                    MXLog.error("\(name): Failed building CollectionDifference from \(diff)")
-                    return currentItems
-                }
-                
-                guard let updatedItems = currentItems.applying(collectionDiff) else {
-                    MXLog.error("\(name): Failed applying diff: \(collectionDiff)")
-                    return currentItems
-                }
-                
-                return updatedItems
+        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))))
+            } else {
+                processDiff(diff)
             }
+        }
         
         detectDuplicatesInRoomList(rooms)
         
         MXLog.info("\(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 {
+            MXLog.error("\(name): Failed building CollectionDifference from \(diff)")
+            return
+        }
+        
+        guard let updatedItems = rooms.applying(collectionDiff) else {
+            MXLog.error("\(name): Failed applying diff: \(collectionDiff)")
+            return
+        }
+        
+        rooms = updatedItems
+    }
 
     private func fetchRoomInfo(roomListItem: RoomListItemProtocol) -> RoomInfo? {
         class FetchResult {