The Book of the Wars of the LORD

Numbers 21:13-15 - They set out from there and camped alongside the Arnon, which is in the desert extending into Amorite territory. The Arnon is the border of Moab, between Moab and the Amorites. That is why the Book of the Wars of the LORD says:

"Waheb in Suphah and the ravines,
the Arnon and the slopes of the ravines
that lead to the site of Ar
and lie along the border of Moab."

I wonder who the author (or authors) of the Book of the Wars of the LORD (BWL) was (or were). I wonder if Moses is quoting it from memory or if he had a copy at his side. Was there more than one copy? Was Moses the author?

I wonder when the BWL was written. How many "Wars of the LORD" did it contain? To this point in Numbers, there hadn't been all that many. Perhaps Moses was writing Numbers years later after there had been more wars that could fill the BWL.

I wonder why Moses quoted the BWL here in Numbers. He mentions the BWL rather matter-of-factly, as if all his readers would have heard of it. I wonder why he felt the need to explain a passage from the BWL here in Numbers. Wasn't it explained well enough in the BWL? I wonder if the BWL refers to or quotes Numbers or any of Moses other books.