RocketChatViewController is a Swift library that Rocket.Chat created to facilitate other teams to have a chat screen inside their applications. The library implements most functionality needed, such as displaying and updating the list of messages with a powerful diffing algorithm; a customizable message composer, with already-implemented features such as message autocompletion, editing, quoting, send and upload buttons.
We've been using RocketChatViewController in our iOS application for a while now so it's very stable and you can already use it in your iOS app.
The architecture of the list is purely inspired in IGListKit and depends on DifferenceKit library to run the differences on the list elements. The whole list is completely UIKit based and works on top of a UICollectionView.