feat: implement database connection and event bus handling

crates/worker/src/event_bus.rs

@@ -0,0 +1,58 @@
+use std::sync::Arc;
+
+use anyhow::Context;
+use domain::ports::{EventConsumer, EventPublisher};
+
+use crate::db::DbPool;
+
+#[derive(Clone, Copy)]
+pub enum EventBusBackend {
+    Db,
+    #[cfg(feature = "nats")]
+    Nats,
+}
+
+impl EventBusBackend {
+    pub fn from_env() -> anyhow::Result<Self> {
+        match std::env::var("EVENT_BUS_BACKEND")
+            .unwrap_or_else(|_| "db".to_string())
+            .as_str()
+        {
+            "db" => Ok(Self::Db),
+            #[cfg(feature = "nats")]
+            "nats" => Ok(Self::Nats),
+            #[cfg(not(feature = "nats"))]
+            "nats" => anyhow::bail!(
+                "EVENT_BUS_BACKEND=nats requires the nats feature to be compiled in"
+            ),
+            other => anyhow::bail!("unknown EVENT_BUS_BACKEND={other}, expected 'db' or 'nats'"),
+        }
+    }
+}
+
+pub async fn create(
+    db_pool: &DbPool,
+) -> anyhow::Result<(Arc<dyn EventPublisher>, Arc<dyn EventConsumer>)> {
+    match EventBusBackend::from_env()? {
+        EventBusBackend::Db => {
+            tracing::info!("event bus: DB queue");
+            match db_pool {
+                #[cfg(feature = "postgres")]
+                DbPool::Postgres(pool) => {
+                    Ok(postgres_event_queue::PostgresEventQueue::create_channel(pool.clone()).await?)
+                }
+                #[cfg(feature = "sqlite")]
+                DbPool::Sqlite(pool) => {
+                    Ok(sqlite_event_queue::SqliteEventQueue::create_channel(pool.clone()).await?)
+                }
+            }
+        }
+        #[cfg(feature = "nats")]
+        EventBusBackend::Nats => {
+            let cfg = nats::NatsConfig::from_env()
+                .context("EVENT_BUS_BACKEND=nats requires NATS_URL to be set")?;
+            tracing::info!("event bus: NATS ({})", cfg.url);
+            Ok(nats::create_channel(cfg).await?)
+        }
+    }
+}