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use std::iter::Fuse;
use alloc::collections::VecDeque;
use crate::size_hint;
use crate::PeekingNext;
#[cfg(doc)]
use crate::Itertools;
/// See [`multipeek()`] for more information.
#[derive(Clone, Debug)]
pub struct MultiPeek<I>
where I: Iterator
{
iter: Fuse<I>,
buf: VecDeque<I::Item>,
index: usize,
}
/// An iterator adaptor that allows the user to peek at multiple `.next()`
/// values without advancing the base iterator.
///
/// [`IntoIterator`] enabled version of [`Itertools::multipeek`].
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
{
/// Reset the peeking “cursor”
pub fn reset_peek(&mut self) {
self.index = 0;
}
}
impl<I: Iterator> MultiPeek<I> {
/// Works exactly like `.next()` with the only difference that it doesn't
/// advance itself. `.peek()` can be called multiple times, to peek
/// further ahead.
/// When `.next()` is called, reset the peeking “cursor”.
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.get(0) {
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())
}
}
// Same size
impl<I> ExactSizeIterator for MultiPeek<I>
where I: ExactSizeIterator
{}