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use std::collections::VecDeque;
use std::ops::{Index, IndexMut};
/// A view onto a finite range of an infinitely long sequence of T.
///
/// The Ts are indexed 0..infinity. A RingBuffer begins as a view of elements
/// 0..0 (i.e. nothing). The user of the RingBuffer advances its left and right
/// position independently, although only in the positive direction, and only
/// with left <= right at all times.
///
/// Holding a RingBuffer whose view is elements left..right gives the ability to
/// use Index and IndexMut to access elements i in the infinitely long queue for
/// which left <= i < right.
pub struct RingBuffer<T> {
data: VecDeque<T>,
// Abstract index of data[0] in the infinitely sized queue.
offset: usize,
}
impl<T> RingBuffer<T> {
pub fn new() -> Self {
RingBuffer { data: VecDeque::new(), offset: 0 }
}
pub fn push(&mut self, value: T) {
self.data.push_back(value);
}
pub fn advance_left(&mut self) {
self.data.pop_front().unwrap();
self.offset += 1;
}
pub fn clear(&mut self) {
self.data.clear();
}
pub fn last(&self) -> Option<&T> {
self.data.back()
}
pub fn last_mut(&mut self) -> Option<&mut T> {
self.data.back_mut()
}
}
impl<T> Index<usize> for RingBuffer<T> {
type Output = T;
fn index(&self, index: usize) -> &Self::Output {
&self.data[index.checked_sub(self.offset).unwrap()]
}
}
impl<T> IndexMut<usize> for RingBuffer<T> {
fn index_mut(&mut self, index: usize) -> &mut Self::Output {
&mut self.data[index.checked_sub(self.offset).unwrap()]
}
}
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