use super::size_hint;
use std::cmp::Ordering::{Equal, Greater, Less};
use std::iter::{Fuse, FusedIterator};
use crate::either_or_both::EitherOrBoth;
#[derive(Clone, Debug)]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct ZipLongest<T, U> {
a: Fuse<T>,
b: Fuse<U>,
}
pub fn zip_longest<T, U>(a: T, b: U) -> ZipLongest<T, U>
where
T: Iterator,
U: Iterator,
{
ZipLongest {
a: a.fuse(),
b: b.fuse(),
}
}
impl<T, U> Iterator for ZipLongest<T, U>
where
T: Iterator,
U: Iterator,
{
type Item = EitherOrBoth<T::Item, U::Item>;
#[inline]
fn next(&mut self) -> Option<Self::Item> {
match (self.a.next(), self.b.next()) {
(None, None) => None,
(Some(a), None) => Some(EitherOrBoth::Left(a)),
(None, Some(b)) => Some(EitherOrBoth::Right(b)),
(Some(a), Some(b)) => Some(EitherOrBoth::Both(a, b)),
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
size_hint::max(self.a.size_hint(), self.b.size_hint())
}
#[inline]
fn fold<B, F>(self, init: B, mut f: F) -> B
where
Self: Sized,
F: FnMut(B, Self::Item) -> B,
{
let Self { mut a, mut b } = self;
let res = a.try_fold(init, |init, a| match b.next() {
Some(b) => Ok(f(init, EitherOrBoth::Both(a, b))),
None => Err(f(init, EitherOrBoth::Left(a))),
});
match res {
Ok(acc) => b.map(EitherOrBoth::Right).fold(acc, f),
Err(acc) => a.map(EitherOrBoth::Left).fold(acc, f),
}
}
}
impl<T, U> DoubleEndedIterator for ZipLongest<T, U>
where
T: DoubleEndedIterator + ExactSizeIterator,
U: DoubleEndedIterator + ExactSizeIterator,
{
#[inline]
fn next_back(&mut self) -> Option<Self::Item> {
match self.a.len().cmp(&self.b.len()) {
Equal => match (self.a.next_back(), self.b.next_back()) {
(None, None) => None,
(Some(a), Some(b)) => Some(EitherOrBoth::Both(a, b)),
(Some(a), None) => Some(EitherOrBoth::Left(a)),
(None, Some(b)) => Some(EitherOrBoth::Right(b)),
},
Greater => self.a.next_back().map(EitherOrBoth::Left),
Less => self.b.next_back().map(EitherOrBoth::Right),
}
}
fn rfold<B, F>(self, mut init: B, mut f: F) -> B
where
F: FnMut(B, Self::Item) -> B,
{
let Self { mut a, mut b } = self;
let a_len = a.len();
let b_len = b.len();
match a_len.cmp(&b_len) {
Equal => {}
Greater => {
init = a
.by_ref()
.rev()
.take(a_len - b_len)
.map(EitherOrBoth::Left)
.fold(init, &mut f)
}
Less => {
init = b
.by_ref()
.rev()
.take(b_len - a_len)
.map(EitherOrBoth::Right)
.fold(init, &mut f)
}
}
a.rfold(init, |acc, item_a| {
f(acc, EitherOrBoth::Both(item_a, b.next_back().unwrap()))
})
}
}
impl<T, U> ExactSizeIterator for ZipLongest<T, U>
where
T: ExactSizeIterator,
U: ExactSizeIterator,
{
}
impl<T, U> FusedIterator for ZipLongest<T, U>
where
T: Iterator,
U: Iterator,
{
}