From 1fc06f2fd58747af182c7538f1cdd3748ace1af0 Mon Sep 17 00:00:00 2001
From: WofWca <wofwca@protonmail.com>
Date: Mon, 7 Oct 2024 22:05:06 +0400
Subject: [PATCH] fix: not scrolling to bottom on sending message

Closes https://github.com/deltachat/deltachat-desktop/issues/4186.
The bug was introduced in fecdbbe3676521dea0f7aee58b9beaef0c7fff4f,
https://github.com/deltachat/deltachat-desktop/pull/4145.
---
 CHANGELOG.md                                |  2 +-
 packages/frontend/src/stores/messagelist.ts | 35 ++++++++++++++++++---
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1cd412db70..0764324646 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,7 +15,7 @@
 - windows 64bit and 32bit protable and setup now have different filenames #4131
 - scroll the selected account into view in the accounts sidebar #4137
 - dev: clarify scrolling-related code #4121
-- improved performance a bit #4145
+- improved performance a bit #4145, #4188
 - show contact / group name when pasting invite link in the search field #4151
 - Update local help (2024-10-02) #4165
 - trim whitepaces when reading from clipboard in qr code reader #4169
diff --git a/packages/frontend/src/stores/messagelist.ts b/packages/frontend/src/stores/messagelist.ts
index 08b0b9a8a5..3321b58c66 100644
--- a/packages/frontend/src/stores/messagelist.ts
+++ b/packages/frontend/src/stores/messagelist.ts
@@ -572,10 +572,37 @@ class MessageListStore extends Store<MessageListState> {
 
           if (messagesAlreadyLoaded) {
             newMessageCache = this.state.messageCache
-            oldestFetchedMessageListItemIndex =
-              this.state.oldestFetchedMessageListItemIndex
-            newestFetchedMessageListItemIndex =
-              this.state.newestFetchedMessageListItemIndex
+
+            // Why do we need `Math.min` / `Math.max` here, instead of simply
+            // keeping `this.state.oldestFetchedMessageListItemIndex`
+            // and `this.state.newestFetchedMessageListItemIndex` as they are?
+            // Because some other code might update the state in such a way
+            // that `messageCache` and these
+            // `(oldest|newest)FetchedMessageListItemIndex` are out of sync:
+            // `messageCache` actually has a message, but
+            // these integers say that the message is not yet fetched.
+            // Namely, this can happen inside of `messageChanged` when
+            // it gets invoked for a not yet fetched message, and it gets
+            // added `messageCache` instead of getting updated.
+            // This, in turn, can happen when you send a message.
+            //
+            // The result would be that we'd fail to jump to message inside of
+            // `MessageList.tsx`, because the message wouldn't be rendered,
+            // because we only render messages that are between
+            // `oldestFetchedMessageListItemIndex` and
+            // `newestFetchedMessageListItemIndex` (see `activeView`).
+            //
+            // TODO it would be ideal to get ensure that we don't corrupt
+            // the state in the first place, but let's make
+            // this workaround for now.
+            oldestFetchedMessageListItemIndex = Math.min(
+              this.state.oldestFetchedMessageListItemIndex,
+              oldestFetchedMessageListItemIndex
+            )
+            newestFetchedMessageListItemIndex = Math.max(
+              this.state.newestFetchedMessageListItemIndex,
+              newestFetchedMessageListItemIndex
+            )
           } else {
             newMessageCache =
               (await loadMessages(