use parking_lot::Mutex;
use std::{ops::AddAssign, sync::Arc};
#[derive(Clone, Debug)]
pub(crate) struct IdSequence<T> {
inner: Arc<Mutex<Inner<T>>>,
}
impl<T: Default + Copy + AddAssign<T> + PartialEq<T> + PartialOrd<T> + From<u8>> IdSequence<T> {
pub(crate) fn new(allow_zero: bool) -> Self {
Self {
inner: Arc::new(Mutex::new(Inner::new(allow_zero))),
}
}
pub(crate) fn next(&self) -> T {
self.inner.lock().next()
}
pub(crate) fn set_max(&self, max: T) {
self.inner.lock().set_max(max)
}
}
#[derive(Debug)]
struct Inner<T> {
allow_zero: bool,
zero: T,
one: T,
max: Option<T>,
id: T,
}
impl<T: Default + Copy + AddAssign<T> + PartialEq<T> + PartialOrd<T> + From<u8>> Inner<T> {
fn new(allow_zero: bool) -> Self {
Self {
allow_zero,
zero: 0.into(),
one: 1.into(),
max: None,
id: T::default(),
}
}
fn set_max(&mut self, max: T) {
self.max = if max == self.zero { None } else { Some(max) };
}
fn next(&mut self) -> T {
if !self.allow_zero && self.id == self.zero {
self.id += self.one;
}
if self.check_max() {
let id = self.id;
self.id += self.one;
id
} else {
self.id = self.zero;
self.next()
}
}
fn check_max(&self) -> bool {
if let Some(max) = self.max {
self.id < max
} else {
true
}
}
}