Arthurian Legend

Good afternoon and happy new year (I'm late) to all of you.
I come, again, with some questions and doubts, two actually.
a) What is the first text with Galahad? Does he appear also in welsh text or only after the Lancelot-Grail?
b) Do you rememeber an old arthurian movie inspired by Mark Twain's work? it had a boy (with a female friend, I think) that attended high school and Morgan was the director of the school and she was evil... sorry, i can't remember much more.
Sorry for troubling again this community with my questions :* and thank you for your attention.