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use super::{coproduct::Either, Context, Continue, Effectful, Event, Poll, Waker};
use std::fmt;
use std::marker::PhantomData;
use std::pin::Pin;
struct Handler<HC: Effectful> {
computation: Pin<Box<HC>>,
waker: Option<Waker<Continue<HC::Output>>>,
}
impl<HC> fmt::Debug for Handler<HC>
where
HC: Effectful + fmt::Debug,
HC::Output: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("Handler")
.field("computation", &self.computation)
.field("waker", &self.waker)
.finish()
}
}
impl<HC: Effectful> Handler<HC> {
fn new(computation: HC) -> Self {
Self {
computation: Box::pin(computation),
waker: None,
}
}
}
pub struct Handled<C, H, HC, E, I>
where
HC: Effectful,
{
source: Option<C>,
handler: H,
handler_stack: Vec<Handler<HC>>,
state: ActiveComputation,
phantom: PhantomData<(E, I)>,
}
impl<C, H, HC, E, I> fmt::Debug for Handled<C, H, HC, E, I>
where
C: fmt::Debug,
H: fmt::Debug,
HC: Effectful + fmt::Debug,
HC::Output: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("Handled")
.field("source", &self.source)
.field("handler", &self.handler)
.field("handler stack", &self.handler_stack)
.field("state", &self.state)
.finish()
}
}
impl<C, H, HC: Effectful, E, I> Handled<C, H, HC, E, I> {
pub(crate) fn new(source: C, handler: H) -> Self {
Handled {
source: Some(source),
handler,
handler_stack: vec![],
state: ActiveComputation::Source,
phantom: PhantomData,
}
}
}
#[derive(Debug)]
enum ActiveComputation {
Source,
Handler,
}
impl<C, Output, Effect, H, HC, HandledEffect, NewOutput, NewEffect, I> Effectful
for Handled<C, H, HC, HandledEffect, I>
where
C: Effectful<Output = Output, Effect = Effect>,
H: FnMut(Event<Output, HandledEffect>) -> HC,
HC: Effectful<Output = NewOutput, Effect = Either<Continue<NewOutput>, NewEffect>>,
Effect: super::coproduct::Subset<HandledEffect, I, Remainder = NewEffect>,
{
type Output = NewOutput;
type Effect = NewEffect;
#[inline]
fn poll(mut self: Pin<&mut Self>, cx: &Context) -> Poll<Self::Output, Self::Effect> {
unsafe {
let this = self.as_mut().get_unchecked_mut();
loop {
match &mut this.state {
ActiveComputation::Source => {
match Pin::new_unchecked(
this.source.as_mut().expect("poll after completion"),
)
.poll(cx)
{
Poll::Event(Event::Complete(v)) => {
this.source = None;
this.state = ActiveComputation::Handler;
let comp = (this.handler)(Event::Complete(v));
this.handler_stack.push(Handler::new(comp));
}
Poll::Event(Event::Effect(e)) => match e.subset() {
Ok(e) => {
this.state = ActiveComputation::Handler;
let comp = (this.handler)(Event::Effect(e));
this.handler_stack.push(Handler::new(comp));
}
Err(rem) => return Poll::effect(rem),
},
Poll::Pending => return Poll::Pending,
}
}
ActiveComputation::Handler => {
let handler = &mut this.handler_stack.last_mut().unwrap().computation;
match handler.as_mut().poll(cx) {
Poll::Event(Event::Complete(v)) => {
this.handler_stack.pop();
if this.handler_stack.is_empty() {
return Poll::complete(v);
} else {
(this.handler_stack.last_mut().unwrap().waker)
.take()
.unwrap()
.wake(v);
}
}
Poll::Event(Event::Effect(Either::A(_, cx))) => {
this.state = ActiveComputation::Source;
this.handler_stack.last_mut().unwrap().waker = Some(cx.waker());
}
Poll::Event(Event::Effect(Either::B(e))) => return Poll::effect(e),
Poll::Pending => return Poll::Pending,
}
}
}
}
}
}
}