1 files changed, 55 insertions, 0 deletions
diff --git a/server/src/state.rs b/server/src/state.rs
new file mode 100644
index 0000000..512bcb3
--- /dev/null
+++ b/server/src/state.rs
@@ -0,0 +1,55 @@
+use std::sync::Arc;
+use tokio::sync::{Mutex as AsyncMutex, Semaphore};
+
+use crate::config::Config;
+
+/// Shared application state. The single SQLite connection is serialized behind
+/// an async mutex; concurrent fetch/backtest work is bounded by semaphores.
+pub struct AppState {
+    pub cfg: Config,
+    pub db: AsyncMutex<rusqlite::Connection>,
+    pub run_sem: Arc<Semaphore>,
+    pub fetch_sem: Arc<Semaphore>,
+}
+
+/// Fixed shared contract alias for handler arguments: the axum State extractor
+/// over `Arc<AppState>`. Handlers take `cx: Cx`, helpers take `&Cx`.
+pub type Cx = axum::extract::State<std::sync::Arc<AppState>>;
+
+/// Legacy alias kept for modules (auth, projects, datasets) whose handlers take
+/// the bare `Arc<AppState>`; both styles are valid extractors for this state.
+pub type S = Arc<AppState>;
+
+impl AppState {
+    /// Lock the connection, run the closure, return its result exactly.
+    /// Never `.await` inside the closure; keep transactions in ONE closure.
+    pub async fn with_db<R>(&self, f: impl FnOnce(&mut rusqlite::Connection) -> R) -> R {
+        let mut db = self.db.lock().await;
+        f(&mut db)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::config::Config;
+
+    #[tokio::test]
+    async fn with_db_returns_closure_result_and_composes() {
+        let cfg = Config::from_env();
+        let conn = rusqlite::Connection::open_in_memory().unwrap();
+        let st = AppState {
+            cfg: cfg.clone(),
+            db: AsyncMutex::new(conn),
+            run_sem: Arc::new(Semaphore::new(1)),
+            fetch_sem: Arc::new(Semaphore::new(1)),
+        };
+        let n: i64 = st.with_db(|db| {
+            db.execute("CREATE TABLE t(x INTEGER)", []).unwrap();
+            db.execute("INSERT INTO t VALUES (42)", []).unwrap();
+            db.query_row("SELECT SUM(x) FROM t", [], |r| r.get(0)).unwrap()
+        }).await;
+        assert_eq!(n, 42);
+        st.with_db(|_db| ()).await;
+    }
+}