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// Copyright 2025 Umberto Gotti <umberto.gotti@umbertogotti.dev>
// Licensed under the Apache License, Version 2.0
// http://www.apache.org/licenses/LICENSE-2.0
macro_rules! define_emit_when_impl {
($($bounds:tt)*) => {
use $crate::ordered_merge::ordered_merge_with_index;
use $crate::types::CombinedState;
use $crate::warn;
use alloc::boxed::Box;
use alloc::sync::Arc;
use alloc::vec;
use alloc::vec::Vec;
use core::fmt::Debug;
use core::pin::Pin;
use fluxion_core::fluxion_mutex::Mutex;
use fluxion_core::into_stream::IntoStream;
use fluxion_core::{Fluxion, StreamItem};
use futures::{Stream, StreamExt};
type SharedState<V, TS> = Arc<Mutex<Option<(V, TS)>>>;
/// Extension trait providing the `emit_when` operator for timestamped streams.
///
/// This operator gates a source stream based on conditions from a filter stream,
/// emitting source values only when the combined state passes a predicate.
pub trait EmitWhenExt<T>: Stream<Item = StreamItem<T>> + Sized
where
T: Fluxion,
T::Inner: Clone + Debug + Ord + Unpin + $($bounds)* 'static,
T::Timestamp: Debug + Ord + Copy + $($bounds)* 'static,
{
/// Emits source stream values only when the filter condition is satisfied.
///
/// This operator maintains the latest values from both the source and filter streams,
/// creating a combined state. Source values are emitted only when this combined state
/// passes the provided filter predicate.
///
/// # Behavior
///
/// - Maintains latest value from both source and filter streams
/// - Evaluates predicate on `CombinedState` containing both values
/// - Emits source value when predicate returns `true`
/// - Both streams must emit at least once before any emission occurs
/// - Preserves temporal ordering of source stream
///
/// # Arguments
///
/// * `filter_stream` - Stream providing filter values for the gate condition
/// * `filter` - Predicate function that receives `CombinedState<T::Inner>` containing
/// `[source_value, filter_value]` and returns `true` to emit.
///
/// # Returns
///
/// A pinned stream of `T` containing source values that pass the filter condition.
fn emit_when<IS>(
self,
filter_stream: IS,
filter: impl Fn(&CombinedState<T::Inner, T::Timestamp>) -> bool + $($bounds)* 'static,
) -> impl Stream<Item = StreamItem<T>>
where
IS: IntoStream<Item = fluxion_core::StreamItem<T>>,
IS::Stream: $($bounds)* 'static;
}
impl<T, S> EmitWhenExt<T> for S
where
S: Stream<Item = StreamItem<T>> + Unpin + $($bounds)* 'static,
T: Fluxion,
T::Inner: Clone + Debug + Ord + Unpin + $($bounds)* 'static,
T::Timestamp: Debug + Ord + Copy + $($bounds)* 'static,
{
fn emit_when<IS>(
self,
filter_stream: IS,
filter: impl Fn(&CombinedState<T::Inner, T::Timestamp>) -> bool + $($bounds)* 'static,
) -> impl Stream<Item = StreamItem<T>>
where
IS: IntoStream<Item = fluxion_core::StreamItem<T>>,
IS::Stream: $($bounds)* 'static,
{
let streams: Vec<Pin<Box<dyn Stream<Item = StreamItem<T>> + $($bounds)*>>> =
vec![Box::pin(self), Box::pin(filter_stream.into_stream())];
let source_value: SharedState<T::Inner, T::Timestamp> = Arc::new(Mutex::new(None));
let filter_value: SharedState<T::Inner, T::Timestamp> = Arc::new(Mutex::new(None));
let filter = Arc::new(filter);
let combined_stream = ordered_merge_with_index(streams).filter_map(move |(item, index)| {
let source_value = Arc::clone(&source_value);
let filter_value = Arc::clone(&filter_value);
let filter = Arc::clone(&filter);
async move {
match item {
StreamItem::Value(ordered_value) => match index {
0 => {
let mut source = source_value.lock();
let filter_val = filter_value.lock();
let timestamp = ordered_value.timestamp();
*source = Some((ordered_value.clone().into_inner(), timestamp));
if let Some((src, src_ts)) = source.as_ref() {
if let Some((filt, filt_ts)) = filter_val.as_ref() {
let combined_state = CombinedState::new(
vec![(src.clone(), *src_ts), (filt.clone(), *filt_ts)],
timestamp,
);
if filter(&combined_state) {
Some(StreamItem::Value(T::with_timestamp(
src.clone(),
*src_ts,
)))
} else {
None
}
} else {
None
}
} else {
None
}
}
1 => {
let mut filter_val = filter_value.lock();
let source = source_value.lock();
let timestamp = ordered_value.timestamp();
*filter_val = Some((ordered_value.clone().into_inner(), timestamp));
if let Some((src, src_ts)) = source.as_ref() {
if let Some((filt, filt_ts)) = filter_val.as_ref() {
let combined_state = CombinedState::new(
vec![(src.clone(), *src_ts), (filt.clone(), *filt_ts)],
timestamp,
);
if filter(&combined_state) {
Some(StreamItem::Value(T::with_timestamp(
src.clone(),
*filt_ts,
)))
} else {
None
}
} else {
None
}
} else {
None
}
}
_ => {
warn!("emit_when: unexpected stream index {} — ignoring", index);
None
}
},
StreamItem::Error(e) => Some(StreamItem::Error(e)),
}
}
});
Box::pin(combined_stream)
}
}
};
}