From 7ab5d3bc1784d435891afb3dafa0b4aa28f1280e Mon Sep 17 00:00:00 2001
From: Alexander Zinchuk <alx.zinchuk@gmail.com>
Date: Sun, 18 Jun 2023 12:04:08 +0200
Subject: [PATCH] Chat List: Fix missing chats on page load

---
 src/hooks/useInfiniteScroll.ts | 43 ++++++++++++++++++----------------
 1 file changed, 23 insertions(+), 20 deletions(-)

diff --git a/src/hooks/useInfiniteScroll.ts b/src/hooks/useInfiniteScroll.ts
index b874350e9..746829688 100644
--- a/src/hooks/useInfiniteScroll.ts
+++ b/src/hooks/useInfiniteScroll.ts
@@ -23,15 +23,14 @@ const useInfiniteScroll = <ListId extends string | number>(
     offsetId?: ListId;
   }>();
 
-  const viewportIdsRef = useRef<ListId[] | undefined>((() => {
-    // Only run once to initialize
-    if (!listIds || requestParamsRef.current) {
-      return undefined;
-    }
-
-    const { newViewportIds } = getViewportSlice(listIds, LoadMoreDirection.Forwards, listSlice, listIds[0]);
-    return newViewportIds;
-  })());
+  const currentStateRef = useRef<{ viewportIds: ListId[]; isOnTop: boolean } | undefined>();
+  if (!currentStateRef.current && listIds && !isDisabled) {
+    const {
+      newViewportIds,
+      newIsOnTop,
+    } = getViewportSlice(listIds, LoadMoreDirection.Forwards, listSlice, listIds[0]);
+    currentStateRef.current = { viewportIds: newViewportIds, isOnTop: newIsOnTop };
+  }
 
   const forceUpdate = useForceUpdate();
 
@@ -42,27 +41,26 @@ const useInfiniteScroll = <ListId extends string | number>(
   const prevListIds = usePrevious(listIds);
   const prevIsDisabled = usePrevious(isDisabled);
   if (listIds && !isDisabled && (listIds !== prevListIds || isDisabled !== prevIsDisabled)) {
-    const viewportIds = viewportIdsRef.current;
-    const isOnTop = viewportIds && viewportIds[0] === listIds[0];
-    const currentMiddleId = !isOnTop && viewportIds ? viewportIds[Math.round(viewportIds.length / 2)] : undefined;
+    const { viewportIds, isOnTop } = currentStateRef.current || {};
+    const currentMiddleId = viewportIds && !isOnTop ? viewportIds[Math.round(viewportIds.length / 2)] : undefined;
     const defaultOffsetId = currentMiddleId && listIds.includes(currentMiddleId) ? currentMiddleId : listIds[0];
     const { offsetId = defaultOffsetId, direction = LoadMoreDirection.Forwards } = requestParamsRef.current || {};
-    const { newViewportIds } = getViewportSlice(listIds, direction, listSlice, offsetId);
+    const { newViewportIds, newIsOnTop } = getViewportSlice(listIds, direction, listSlice, offsetId);
 
     requestParamsRef.current = {};
 
     if (!viewportIds || !areSortedArraysEqual(viewportIds, newViewportIds)) {
-      viewportIdsRef.current = newViewportIds;
+      currentStateRef.current = { viewportIds: newViewportIds, isOnTop: newIsOnTop };
     }
   } else if (!listIds) {
-    viewportIdsRef.current = undefined;
+    currentStateRef.current = undefined;
   }
 
   const getMore: GetMore = useLastCallback(({
     direction,
     noScroll,
   }: { direction: LoadMoreDirection; noScroll?: boolean }) => {
-    const viewportIds = viewportIdsRef.current;
+    const { viewportIds } = currentStateRef.current || {};
 
     const offsetId = viewportIds
       ? direction === LoadMoreDirection.Backwards ? viewportIds[viewportIds.length - 1] : viewportIds[0]
@@ -77,11 +75,11 @@ const useInfiniteScroll = <ListId extends string | number>(
     }
 
     const {
-      newViewportIds, areSomeLocal, areAllLocal,
+      newViewportIds, areSomeLocal, areAllLocal, newIsOnTop,
     } = getViewportSlice(listIds, direction, listSlice, offsetId);
 
     if (areSomeLocal && !(viewportIds && areSortedArraysEqual(viewportIds, newViewportIds))) {
-      viewportIdsRef.current = newViewportIds;
+      currentStateRef.current = { viewportIds: newViewportIds, isOnTop: newIsOnTop };
       forceUpdate();
     }
 
@@ -94,7 +92,7 @@ const useInfiniteScroll = <ListId extends string | number>(
     }
   });
 
-  return isDisabled ? [listIds] : [viewportIdsRef.current, getMore];
+  return isDisabled ? [listIds] : [currentStateRef.current?.viewportIds, getMore];
 };
 
 function getViewportSlice<ListId extends string | number>(
@@ -124,7 +122,12 @@ function getViewportSlice<ListId extends string | number>(
       break;
   }
 
-  return { newViewportIds, areSomeLocal, areAllLocal };
+  return {
+    newViewportIds,
+    areSomeLocal,
+    areAllLocal,
+    newIsOnTop: newViewportIds[0] === sourceIds[0],
+  };
 }
 
 export default useInfiniteScroll;