https://mangadex.org/chapter/1014758/12
the "Hai-desu" is essentially saying "I got it!" or "I've got it!"
the literal translation is more of a Japanese colloquial vernacular than it is a grammatically correct statement.
"Hai" is a generic positive/affirmative and can be used on it's own for this context, but "desu" as a suffix is literally an addon to emphasize the moe of a cute girl.
@cullinaire has the idea of the translation, but the term is extremely flexible.