movies-diary/crates/application/src/worker.rs

use std::sync::Arc;

use domain::{
    events::EventEnvelope,
    ports::{EventConsumer, EventHandler},
};
use futures::StreamExt;

pub struct WorkerService {
    consumer: Arc<dyn EventConsumer>,
    handlers: Vec<Arc<dyn EventHandler>>,
}

impl WorkerService {
    pub fn new(consumer: Arc<dyn EventConsumer>, handlers: Vec<Arc<dyn EventHandler>>) -> Self {
        Self { consumer, handlers }
    }

    pub async fn run(self) {
        let mut stream = self.consumer.consume();
        while let Some(result) = stream.next().await {
            match result {
                Ok(envelope) => {
                    tracing::info!(event = ?envelope.event, "received event");
                    self.dispatch(envelope).await;
                }
                Err(e) => tracing::error!("event consumer error: {e}"),
            }
        }
        tracing::info!("event stream ended, worker shutting down");
    }

    async fn dispatch(&self, envelope: EventEnvelope) {
        let mut all_ok = true;
        for handler in &self.handlers {
            if let Err(e) = handler.handle(&envelope.event).await {
                tracing::error!("event handler error: {e}");
                all_ok = false;
            }
        }
        let result = if all_ok {
            envelope.ack().await
        } else {
            envelope.nack().await
        };
        if let Err(e) = result {
            tracing::error!("ack/nack failed: {e}");
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use async_trait::async_trait;
    use domain::{errors::DomainError, events::{AckHandle, DomainEvent}};
    use domain::value_objects::{ExternalMetadataId, MovieId};
    use futures::{stream, stream::BoxStream};
    use std::sync::{Arc, Mutex};

    struct NoopAck;

    #[async_trait]
    impl AckHandle for NoopAck {
        async fn ack(&self) -> Result<(), DomainError> { Ok(()) }
        async fn nack(&self) -> Result<(), DomainError> { Ok(()) }
    }

    struct VecConsumer {
        events: Vec<DomainEvent>,
    }

    impl EventConsumer for VecConsumer {
        fn consume(&self) -> BoxStream<'_, Result<EventEnvelope, DomainError>> {
            let envelopes: Vec<Result<EventEnvelope, DomainError>> = self
                .events
                .iter()
                .cloned()
                .map(|e| Ok(EventEnvelope::new(e, Box::new(NoopAck))))
                .collect();
            Box::pin(stream::iter(envelopes))
        }
    }

    struct RecordingHandler {
        calls: Arc<Mutex<Vec<&'static str>>>,
    }

    #[async_trait]
    impl EventHandler for RecordingHandler {
        async fn handle(&self, event: &DomainEvent) -> Result<(), DomainError> {
            let label = match event {
                DomainEvent::MovieDiscovered { .. } => "movie_discovered",
                DomainEvent::ReviewLogged { .. } => "review_logged",
                DomainEvent::ReviewUpdated { .. } => "review_updated",
            };
            self.calls.lock().unwrap().push(label);
            Ok(())
        }
    }

    fn movie_discovered() -> DomainEvent {
        DomainEvent::MovieDiscovered {
            movie_id: MovieId::generate(),
            external_metadata_id: ExternalMetadataId::new("tt1234567".into()).unwrap(),
        }
    }

    #[tokio::test]
    async fn dispatches_to_all_handlers() {
        let calls = Arc::new(Mutex::new(vec![]));
        let consumer = VecConsumer { events: vec![movie_discovered()] };
        let handler = RecordingHandler { calls: Arc::clone(&calls) };

        WorkerService::new(Arc::new(consumer), vec![Arc::new(handler)])
            .run()
            .await;

        assert_eq!(*calls.lock().unwrap(), vec!["movie_discovered"]);
    }

    #[tokio::test]
    async fn nacks_when_handler_fails() {
        let nack_called = Arc::new(Mutex::new(false));

        struct TrackingAck {
            nack_called: Arc<Mutex<bool>>,
        }

        #[async_trait]
        impl AckHandle for TrackingAck {
            async fn ack(&self) -> Result<(), DomainError> { Ok(()) }
            async fn nack(&self) -> Result<(), DomainError> {
                *self.nack_called.lock().unwrap() = true;
                Ok(())
            }
        }

        struct TrackingConsumer {
            event: DomainEvent,
            nack_called: Arc<Mutex<bool>>,
        }

        impl EventConsumer for TrackingConsumer {
            fn consume(&self) -> BoxStream<'_, Result<EventEnvelope, DomainError>> {
                let envelope = EventEnvelope::new(
                    self.event.clone(),
                    Box::new(TrackingAck { nack_called: Arc::clone(&self.nack_called) }),
                );
                Box::pin(stream::iter(vec![Ok(envelope)]))
            }
        }

        struct FailingHandler;

        #[async_trait]
        impl EventHandler for FailingHandler {
            async fn handle(&self, _: &DomainEvent) -> Result<(), DomainError> {
                Err(DomainError::InfrastructureError("boom".into()))
            }
        }

        let consumer = TrackingConsumer {
            event: movie_discovered(),
            nack_called: Arc::clone(&nack_called),
        };

        WorkerService::new(Arc::new(consumer), vec![Arc::new(FailingHandler)])
            .run()
            .await;

        assert!(*nack_called.lock().unwrap());
    }

    #[tokio::test]
    async fn acks_when_all_handlers_succeed() {
        let ack_called = Arc::new(Mutex::new(false));

        struct TrackingAck {
            ack_called: Arc<Mutex<bool>>,
        }

        #[async_trait]
        impl AckHandle for TrackingAck {
            async fn ack(&self) -> Result<(), DomainError> {
                *self.ack_called.lock().unwrap() = true;
                Ok(())
            }
            async fn nack(&self) -> Result<(), DomainError> { Ok(()) }
        }

        struct TrackingConsumer {
            event: DomainEvent,
            ack_called: Arc<Mutex<bool>>,
        }

        impl EventConsumer for TrackingConsumer {
            fn consume(&self) -> BoxStream<'_, Result<EventEnvelope, DomainError>> {
                let envelope = EventEnvelope::new(
                    self.event.clone(),
                    Box::new(TrackingAck { ack_called: Arc::clone(&self.ack_called) }),
                );
                Box::pin(stream::iter(vec![Ok(envelope)]))
            }
        }

        let consumer = TrackingConsumer {
            event: movie_discovered(),
            ack_called: Arc::clone(&ack_called),
        };

        WorkerService::new(Arc::new(consumer), vec![])
            .run()
            .await;

        assert!(*ack_called.lock().unwrap());
    }
}