books for folk guitar with advanced fingerpicking exercises (blues, country, folk)?

I picked up a country music book recently and realized that it's definitely more stimulating to read on a piece of paper.

I like folk (Linda Perhacs, Jackson C Frank, Nick Drake…) ,baroque folk (like Bert Jansch) and american primitivism (John Fahey), however I would like to delve deeper into blues (I love Skip James) and country (I love Leo Kottle, and in the last book I discovered Sam McGee that is really cool too) , but all advice is welcome regarding these genres!

I feel at a good level so I would like something even difficult that I can spend days learning.

I would prefer to avoid genres such as flamenco, jazz or bossa nova for the moment