Prior to this commit we were loading a large number of thread messages without any pagination. This commit attempts to fix this and also improves the following points:
- code sharing between channels and threads:
Attempts to reuse/share the code use in channels for threads. To make it possible part of this code has been extracted in dedicated helpers or has been improved to reduce the duplication needed.
Examples of extracted helpers:
- `stackingContextFix`: the ios hack for rendering bug when momentum scrolling is interrupted
- `scrollListToMessage`, `scrollListToTop`, `scrollListToBottom`: a series of helper to correctly scroll to a specific position in the list of messages
- better general performance of listing messages:
One of the main changes which has been made is to remove the computation of visible message during scroll, it will only happen when needed (update last read for example). This constant recomputation of `message.visible` on intersection observer event while scrolling was consuming a lot of CPU time.
This issue was for example possibly causing the last visit indicator to be reset by `sent` messages events.
The following was happening:
- a user (bob) had a last message bus ID of 1 on a channel (id:1) subscription
- bob then go to another channel (id:2), unsubscribing from updates of channel (id:1)
- another user (laura) then send messages to channel (id:1)
- bob goes back to channel (id:1)
At this point we we doing in the same sequence:
- loading channel with messages, getting a new last message bus id
- subscribing to updates using the last known message bus id
Most of the times we were lucky enough for this to work (no events while away, or just got the new id in time...) but it was also very likely to do a double fetch of messages as MessageBus would think we were late.
