grammar - Is "What did you just say" grammatically correct?

Should I say:

What did you just say?

or

What have you just said?

I find the first one more common.

The English grammar textbooks I've read emphasized that "just" refers to the present therefore you should use present perfect tense in such situations. For example, in an affirmative sentence, you'll definitely say "I've just finished reading this book" rather than "I just finished reading this book", right? Then what about questions like the one above?