use crate::size_hint;
#[cfg(doc)]
use crate::Itertools;
use crate::PeekingNext;
use alloc::collections::VecDeque;
use std::iter::Fuse;
#[derive(Clone, Debug)]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct MultiPeek<I>
where
I: Iterator,
{
iter: Fuse<I>,
buf: VecDeque<I::Item>,
index: usize,
}
pub fn multipeek<I>(iterable: I) -> MultiPeek<I::IntoIter>
where
I: IntoIterator,
{
MultiPeek {
iter: iterable.into_iter().fuse(),
buf: VecDeque::new(),
index: 0,
}
}
impl<I> MultiPeek<I>
where
I: Iterator,
{
pub fn reset_peek(&mut self) {
self.index = 0;
}
}
impl<I: Iterator> MultiPeek<I> {
pub fn peek(&mut self) -> Option<&I::Item> {
let ret = if self.index < self.buf.len() {
Some(&self.buf[self.index])
} else {
match self.iter.next() {
Some(x) => {
self.buf.push_back(x);
Some(&self.buf[self.index])
}
None => return None,
}
};
self.index += 1;
ret
}
}
impl<I> PeekingNext for MultiPeek<I>
where
I: Iterator,
{
fn peeking_next<F>(&mut self, accept: F) -> Option<Self::Item>
where
F: FnOnce(&Self::Item) -> bool,
{
if self.buf.is_empty() {
if let Some(r) = self.peek() {
if !accept(r) {
return None;
}
}
} else if let Some(r) = self.buf.front() {
if !accept(r) {
return None;
}
}
self.next()
}
}
impl<I> Iterator for MultiPeek<I>
where
I: Iterator,
{
type Item = I::Item;
fn next(&mut self) -> Option<Self::Item> {
self.index = 0;
self.buf.pop_front().or_else(|| self.iter.next())
}
fn size_hint(&self) -> (usize, Option<usize>) {
size_hint::add_scalar(self.iter.size_hint(), self.buf.len())
}
fn fold<B, F>(self, mut init: B, mut f: F) -> B
where
F: FnMut(B, Self::Item) -> B,
{
init = self.buf.into_iter().fold(init, &mut f);
self.iter.fold(init, f)
}
}
impl<I> ExactSizeIterator for MultiPeek<I> where I: ExactSizeIterator {}