Problem with implement the equiv of git pull

I am working my way through an implementation of git pull.

It seems that I need to do a Remote.fetch() call followed by a merge.

Problem (1): what is the robust way to generate the fetch_refspecs if the REmote.fetch_refspecs is empty? In other words do you have the APIs that I can duplciaste what push.default=simple causes git pull to do?

Problem (2): I have the objects fetched back I do not know the API to call to merge the remote changed into the local. I tried calling repo.merge() with the ID of the lastest commit from the remote.
But that only lead to modified files in the index. What is the correct API code to make this work?

Start by reading the Remote.fetch, Remote.fetch_refspecs, and Repository.merge APIs mentioned in the issue, along with how git pull uses push.default=simple. Determine the supported fetch and merge sequence, then confirm that fetched remote changes are merged into the local repository rather than only leaving index modifications.