thoughts/crates/adapters/nats/src/lib.rs

use async_trait::async_trait;
use domain::errors::DomainError;
use event_transport::{MessageSource, RawMessage, Transport};
use futures::stream::BoxStream;

// ── NatsTransport — raw NATS publish backend ────────────────────────────────

pub struct NatsTransport {
    client: async_nats::Client,
}

impl NatsTransport {
    pub fn new(client: async_nats::Client) -> Self {
        Self { client }
    }
}

#[async_trait]
impl Transport for NatsTransport {
    async fn publish_bytes(&self, subject: &str, bytes: &[u8]) -> Result<(), DomainError> {
        self.client
            .publish(subject.to_string(), bytes.to_vec().into())
            .await
            .map_err(|e| DomainError::Internal(e.to_string()))
    }
}

// ── NatsMessageSource — raw NATS subscribe backend ──────────────────────────

pub struct NatsMessageSource {
    client: async_nats::Client,
}

impl NatsMessageSource {
    pub fn new(client: async_nats::Client) -> Self {
        Self { client }
    }
}

impl MessageSource for NatsMessageSource {
    fn messages(&self) -> BoxStream<'_, Result<RawMessage, DomainError>> {
        let client = self.client.clone();
        Box::pin(async_stream::try_stream! {
            let mut sub = client
                .subscribe(">")
                .await
                .map_err(|e| DomainError::Internal(e.to_string()))?;

            use futures::StreamExt;
            while let Some(msg) = sub.next().await {
                let subject = msg.subject.to_string();
                let payload = msg.payload.to_vec();
                // Basic NATS: at-most-once — ack/nack are no-ops.
                yield RawMessage {
                    subject,
                    payload,
                    ack:  Box::new(|| {}),
                    nack: Box::new(|| {}),
                };
            }
        })
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use domain::{
        events::DomainEvent,
        value_objects::{LikeId, ThoughtId, UserId},
    };
    use event_payload::EventPayload;

    #[test]
    fn payload_from_domain_event_has_correct_subject() {
        let event = DomainEvent::ThoughtCreated {
            thought_id: ThoughtId::new(),
            user_id: UserId::new(),
            in_reply_to_id: None,
        };
        let payload = EventPayload::from(&event);
        assert_eq!(payload.subject(), "thoughts.created");
    }

    #[test]
    fn domain_event_roundtrip_via_payload() {
        let uid = UserId::new();
        let tid = ThoughtId::new();
        let event = DomainEvent::LikeAdded {
            like_id: LikeId::new(),
            user_id: uid.clone(),
            thought_id: tid.clone(),
        };
        let payload = EventPayload::from(&event);
        let back = DomainEvent::try_from(payload).unwrap();
        if let DomainEvent::LikeAdded {
            user_id,
            thought_id,
            ..
        } = back
        {
            assert_eq!(user_id, uid);
            assert_eq!(thought_id, tid);
        } else {
            panic!("wrong variant");
        }
    }
}