https://news.ycombinator.com/item?id=20603567, discussing https://viewsourcecode.org/snaptoken/kilo/index.html probably will give you some hints.

Architecture-wise, you can start with an ordered list of lines, with each line stored as a string.

Features that complicate things are:

- supporting large documents and staying speedy (“replace all” is a good test case)

- supporting line wrapping or proportional fonts (makes it harder to translate between screen locations and (line, character) offsets)

- supporting Unicode (makes it harder to translate between screen locations and (line, byte position) offsets)

- syntax-colouring

- plug-ins

- regular expression based search (fairly simple for single-line search _if_ you store each line as a string; harder for custom data structures, as you can’t just use a regexp library)

- supporting larger-than-memory files (especially on systems without virtual memory, but I think that’s somewhat of a lost art)

- safely saving documents even if the disk doesn’t have space for two files (a lost art. Might not even have been fully solved, ever)

Edit: you also want to look at https://news.ycombinator.com/item?id=11244103, discussing https://ecc-comp.blogspot.com/2015/05/a-brief-glance-at-how-...