This is the source for the flutter editor under 1000 lines of code - as written for the article at medium:
This project is for article purposes onl - for tutorial or for proof of concept. A more complete editor is flutter_editor:
https://github.com/icedman/flutter_editor
And some concepts here are used in the more advanced android app Ashlar Code (http://www.munchyapps.com/)