continuwuity/src/core/utils/algorithm.rs

use std::cmp::Ordering;

#[allow(clippy::impl_trait_in_params)]
pub fn common_elements(
	mut iterators: impl Iterator<Item = impl Iterator<Item = Vec<u8>>>, check_order: impl Fn(&[u8], &[u8]) -> Ordering,
) -> Option<impl Iterator<Item = Vec<u8>>> {
	let first_iterator = iterators.next()?;
	let mut other_iterators = iterators.map(Iterator::peekable).collect::<Vec<_>>();

	Some(first_iterator.filter(move |target| {
		other_iterators.iter_mut().all(|it| {
			while let Some(element) = it.peek() {
				match check_order(element, target) {
					Ordering::Greater => return false, // We went too far
					Ordering::Equal => return true,    // Element is in both iters
					Ordering::Less => {
						// Keep searching
						it.next();
					},
				}
			}
			false
		})
	}))
}