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use arc_swap::ArcSwapOption;
use std::sync::Arc;
use crate::{Message, Source};
/// Callbag operator that flattens a higher-order callbag source.
///
/// Like [ReactiveX `switch`][reactivex-switch] or [xstream `flatten`][xstream-flatten]. Use it
/// with [`map`] to get behavior equivalent to [RxJS `switchMap`][rxjs-switch-map].
///
/// Works on either pullable or listenable sources.
///
/// See <https://github.com/staltz/callbag-flatten/blob/9d08c8807802243517697dd7401a9d5d2ba69c24/index.js#L1-L43>
///
/// # Examples
///
/// ## Listenables
///
/// ## Pullables
///
/// Loop over two iterables (such as arrays) and combine their values together:
///
/// ```
/// use crossbeam_queue::SegQueue;
/// use std::sync::Arc;
///
/// use callbag::{flatten, for_each, from_iter, map, pipe};
///
/// let actual = Arc::new(SegQueue::new());
///
/// let source = pipe!(
/// from_iter("hi".chars()),
/// map(|r#char| pipe!(
/// from_iter([10, 20, 30]),
/// map(move |num| format!("{}{}", r#char, num)),
/// )),
/// flatten,
/// for_each({
/// let actual = Arc::clone(&actual);
/// move |x: String| {
/// println!("{}", x);
/// actual.push(x.clone());
/// }
/// }),
/// );
///
/// assert_eq!(
/// &{
/// let mut v = vec![];
/// for _i in 0..actual.len() {
/// v.push(actual.pop().unwrap());
/// }
/// v
/// }[..],
/// ["h10", "h20", "h30", "i10", "i20", "i30"]
/// );
/// ```
///
/// [`map`]: crate::map()
/// [reactivex-switch]: https://reactivex.io/documentation/operators/switch.html
/// [rxjs-switch-map]: https://rxjs.dev/api/operators/switchMap
/// [xstream-flatten]: https://github.com/staltz/xstream#flatten
pub fn flatten<T: 'static, S, R: 'static>(source: S) -> Source<T>
where
S: Into<Arc<Source<R>>>,
R: Into<Arc<Source<T>>>,
{
let source: Arc<Source<R>> = source.into();
(move |message| {
if let Message::Handshake(sink) = message {
let outer_talkback: Arc<ArcSwapOption<Source<R>>> = Arc::new(ArcSwapOption::from(None));
let inner_talkback: Arc<ArcSwapOption<Source<T>>> = Arc::new(ArcSwapOption::from(None));
let talkback: Arc<Source<T>> = Arc::new(
{
let outer_talkback = Arc::clone(&outer_talkback);
let inner_talkback = Arc::clone(&inner_talkback);
move |message| match message {
Message::Handshake(_) => {
panic!("sink handshake has already occurred");
},
Message::Data(_) => {
panic!("sink must not send data");
},
Message::Pull => {
if let Some(inner_talkback) = &*inner_talkback.load() {
inner_talkback(Message::Pull);
} else if let Some(outer_talkback) = &*outer_talkback.load() {
outer_talkback(Message::Pull);
}
},
Message::Error(_) | Message::Terminate => {
if let Some(inner_talkback) = &*inner_talkback.load() {
inner_talkback(Message::Terminate);
}
if let Some(outer_talkback) = &*outer_talkback.load() {
outer_talkback(Message::Terminate);
}
},
}
}
.into(),
);
source(Message::Handshake(Arc::new(
(move |message| {
let sink = Arc::clone(&sink);
let outer_talkback = Arc::clone(&outer_talkback);
let inner_talkback = Arc::clone(&inner_talkback);
match message {
Message::Handshake(source) => {
outer_talkback.store(Some(source));
sink(Message::Handshake(Arc::clone(&talkback)));
},
Message::Data(inner_source) => {
let inner_source: Arc<Source<T>> = inner_source.into();
if let Some(inner_talkback) = &*inner_talkback.load() {
inner_talkback(Message::Terminate);
}
inner_source(Message::Handshake(Arc::new(
(move |message| match message {
Message::Handshake(source) => {
inner_talkback.store(Some(source));
let inner_talkback = inner_talkback.load();
let inner_talkback = inner_talkback
.as_ref()
.expect("inner source talkback not set");
inner_talkback(Message::Pull);
},
Message::Data(data) => {
sink(Message::Data(data));
},
Message::Pull => {
panic!("source must not pull");
},
Message::Error(error) => {
if let Some(outer_talkback) = &*outer_talkback.load() {
outer_talkback(Message::Terminate);
}
sink(Message::Error(error));
},
Message::Terminate => {
if outer_talkback.load().is_none() {
sink(Message::Terminate);
} else {
inner_talkback.store(None);
let outer_talkback = outer_talkback.load();
let outer_talkback = outer_talkback
.as_ref()
.expect("outer source talkback not set");
outer_talkback(Message::Pull);
}
},
})
.into(),
)));
},
Message::Pull => {
panic!("source must not pull");
},
Message::Error(error) => {
if let Some(inner_talkback) = &*inner_talkback.load() {
inner_talkback(Message::Terminate);
}
sink(Message::Error(error));
},
Message::Terminate => {
if inner_talkback.load().is_none() {
sink(Message::Terminate);
} else {
outer_talkback.store(None);
}
},
}
})
.into(),
)));
}
})
.into()
}