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use arc_swap::ArcSwapOption;
use std::sync::{
atomic::{AtomicUsize, Ordering as AtomicOrdering},
Arc,
};
use crate::{Message, Source};
/// Callbag operator that skips the first N data points of a source.
///
/// Works on either pullable and listenable sources.
///
/// See <https://github.com/staltz/callbag-skip/blob/698d6b7805c9bcddac038ceff25a0f0362adb25a/index.js#L1-L18>
///
/// # Examples
///
/// On a listenable source:
///
/// ```
/// use async_executors::TimerExt;
/// use async_nursery::Nursery;
/// use crossbeam_queue::SegQueue;
/// use std::{sync::Arc, time::Duration};
///
/// use callbag::{for_each, interval, skip};
///
/// let (nursery, nursery_out) = Nursery::new(async_executors::AsyncStd);
///
/// let actual = Arc::new(SegQueue::new());
///
/// let source = skip(3)(interval(Duration::from_millis(1_000), nursery.clone()));
///
/// for_each({
/// let actual = Arc::clone(&actual);
/// move |x| {
/// println!("{}", x);
/// actual.push(x);
/// }
/// })(source);
///
/// let nursery_out = nursery.timeout(Duration::from_millis(7_500), nursery_out);
/// drop(nursery);
/// async_std::task::block_on(nursery_out);
///
/// assert_eq!(
/// &{
/// let mut v = vec![];
/// for _i in 0..actual.len() {
/// v.push(actual.pop().unwrap());
/// }
/// v
/// }[..],
/// [3, 4, 5, 6]
/// );
/// ```
///
/// On a pullable source:
///
/// ```
/// use crossbeam_queue::SegQueue;
/// use std::sync::Arc;
///
/// use callbag::{for_each, from_iter, skip};
///
/// #[derive(Clone)]
/// struct Range {
/// i: usize,
/// to: usize,
/// }
///
/// impl Range {
/// fn new(from: usize, to: usize) -> Self {
/// Range { i: from, to }
/// }
/// }
///
/// impl Iterator for Range {
/// type Item = usize;
///
/// fn next(&mut self) -> Option<Self::Item> {
/// let i = self.i;
/// if i <= self.to {
/// self.i += 1;
/// Some(i)
/// } else {
/// None
/// }
/// }
/// }
///
/// let actual = Arc::new(SegQueue::new());
///
/// let source = skip(4)(from_iter(Range::new(10, 20)));
///
/// for_each({
/// let actual = Arc::clone(&actual);
/// move |x| {
/// println!("{}", x);
/// actual.push(x);
/// }
/// })(source);
///
/// assert_eq!(
/// &{
/// let mut v = vec![];
/// for _i in 0..actual.len() {
/// v.push(actual.pop().unwrap());
/// }
/// v
/// }[..],
/// [14, 15, 16, 17, 18, 19, 20]
/// );
/// ```
pub fn skip<T: 'static, S>(max: usize) -> Box<dyn Fn(S) -> Source<T>>
where
S: Into<Arc<Source<T>>>,
{
Box::new(move |source| {
let source: Arc<Source<T>> = source.into();
(move |message| {
if let Message::Handshake(sink) = message {
let skipped = Arc::new(AtomicUsize::new(0));
let talkback: Arc<ArcSwapOption<Source<T>>> = Arc::new(ArcSwapOption::from(None));
source(Message::Handshake(Arc::new(
(move |message| match message {
Message::Handshake(source) => {
talkback.store(Some(source));
sink(Message::Handshake(Arc::new(
{
let talkback = Arc::clone(&talkback);
move |message| match message {
Message::Handshake(_) => {
panic!("sink handshake has already occurred");
},
Message::Data(_) => {
panic!("sink must not send data");
},
Message::Pull => {
let talkback = talkback.load();
let source =
talkback.as_ref().expect("source talkback not set");
source(Message::Pull);
},
Message::Error(error) => {
let talkback = talkback.load();
let source =
talkback.as_ref().expect("source talkback not set");
source(Message::Error(error));
},
Message::Terminate => {
let talkback = talkback.load();
let source =
talkback.as_ref().expect("source talkback not set");
source(Message::Terminate);
},
}
}
.into(),
)));
},
Message::Data(data) => {
if skipped.load(AtomicOrdering::Acquire) < max {
skipped.fetch_add(1, AtomicOrdering::AcqRel);
{
let talkback = talkback.load();
let talkback =
talkback.as_ref().expect("source talkback not set");
talkback(Message::Pull);
}
} else {
sink(Message::Data(data));
}
},
Message::Pull => {
panic!("source must not pull");
},
Message::Error(error) => {
sink(Message::Error(error));
},
Message::Terminate => {
sink(Message::Terminate);
},
})
.into(),
)))
}
})
.into()
})
}