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;
    }
}