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use slab::Slab;
#[derive(Debug)]
pub struct Buffer<T> {
slab: Slab<Slot<T>>,
}
#[derive(Debug)]
pub struct Deque {
indices: Option<Indices>,
}
#[derive(Debug, Default, Copy, Clone)]
struct Indices {
head: usize,
tail: usize,
}
#[derive(Debug)]
struct Slot<T> {
value: T,
next: Option<usize>,
}
impl<T> Buffer<T> {
pub fn new() -> Self {
Buffer {
slab: Slab::new(),
}
}
}
impl Deque {
pub fn new() -> Self {
Deque {
indices: None,
}
}
pub fn is_empty(&self) -> bool {
self.indices.is_none()
}
pub fn push_back<T>(&mut self, buf: &mut Buffer<T>, value: T) {
let key = buf.slab.insert(Slot {
value,
next: None,
});
match self.indices {
Some(ref mut idxs) => {
buf.slab[idxs.tail].next = Some(key);
idxs.tail = key;
},
None => {
self.indices = Some(Indices {
head: key,
tail: key,
});
},
}
}
pub fn push_front<T>(&mut self, buf: &mut Buffer<T>, value: T) {
let key = buf.slab.insert(Slot {
value,
next: None,
});
match self.indices {
Some(ref mut idxs) => {
buf.slab[key].next = Some(idxs.head);
idxs.head = key;
},
None => {
self.indices = Some(Indices {
head: key,
tail: key,
});
},
}
}
pub fn pop_front<T>(&mut self, buf: &mut Buffer<T>) -> Option<T> {
match self.indices {
Some(mut idxs) => {
let mut slot = buf.slab.remove(idxs.head);
if idxs.head == idxs.tail {
assert!(slot.next.is_none());
self.indices = None;
} else {
idxs.head = slot.next.take().unwrap();
self.indices = Some(idxs);
}
return Some(slot.value);
},
None => None,
}
}
pub fn peek_front<'a, T>(&self, buf: &'a Buffer<T>) -> Option<&'a T> {
match self.indices {
Some(idxs) => Some(&buf.slab[idxs.head].value),
None => None,
}
}
}