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//! Module for [`Reactor`].

use tokio::sync::mpsc::error::SendError;
use tokio::sync::mpsc::UnboundedSender;

use super::SubgraphId;

/// A handle into a specific [super::graph::Dfir] instance for triggering
/// subgraphs to run, possibly from another thread.
///
/// Reactor events are considered to be external events.
#[derive(Clone)]
pub struct Reactor {
    event_queue_send: UnboundedSender<(SubgraphId, bool)>,
}
impl Reactor {
    pub(crate) fn new(event_queue_send: UnboundedSender<(SubgraphId, bool)>) -> Self {
        Self { event_queue_send }
    }

    /// Trigger a subgraph as an external event.
    pub fn trigger(&self, sg_id: SubgraphId) -> Result<(), SendError<(SubgraphId, bool)>> {
        self.event_queue_send.send((sg_id, true))
    }

    /// Convert this `Reactor` into a [`std::task::Waker`] for use with async runtimes.
    pub fn into_waker(self, sg_id: SubgraphId) -> std::task::Waker {
        use std::sync::Arc;

        use futures::task::ArcWake;

        struct ReactorWaker {
            reactor: Reactor,
            sg_id: SubgraphId,
        }
        impl ArcWake for ReactorWaker {
            fn wake_by_ref(arc_self: &Arc<Self>) {
                arc_self.reactor.trigger(arc_self.sg_id).unwrap(/* TODO(mingwei) */);
            }
        }

        let reactor_waker = ReactorWaker {
            reactor: self,
            sg_id,
        };
        futures::task::waker(Arc::new(reactor_waker))
    }
}