use tokio::sync::{mpsc, oneshot};
fn create_tables(conn: &sqlite::Connection) -> sqlite::Result<()> {
    conn.execute("CREATE TABLE IF NOT EXISTS names (name TEXT)")?;
    conn.execute(
        "CREATE TABLE IF NOT EXISTS preferences (
            better INTEGER,
            worse INTEGER,
            FOREIGN KEY (better) REFERENCES names(rowid) ON DELETE CASCADE,
            FOREIGN KEY (worse) REFERENCES names(rowid) ON DELETE CASCADE,
            UNIQUE(better,worse))",
    )?;
    Ok(())
}
struct AsyncConnection(
    mpsc::Sender<Box<dyn for<'a> FnOnce(&'a sqlite::Connection) + Send>>,
);
impl AsyncConnection {
    pub async fn open<T: AsRef<std::path::Path> + Send + 'static>(
        path: T,
    ) -> Result<Self, Box<dyn std::error::Error>> {
        let (tx, mut rx): (
            _,
            mpsc::Receiver<Box<dyn for<'a> FnOnce(&sqlite::Connection) + Send>>,
        ) = mpsc::channel(1);
        std::thread::Builder::new()
            .name(format!("database thread: {}", path.as_ref().display()))
            .spawn(move || {
                let conn = sqlite::open(path).unwrap();
                while let Some(cb) = rx.blocking_recv() {
                    cb(&conn);
                }
            })?;
        let result = Self(tx);
        result.post(create_tables).await??;
        Ok(result)
    }
    async fn post<
        F: FnOnce(&sqlite::Connection) -> U + Send + 'static,
        U: Send + 'static,
    >(
        &self,
        cb: F,
    ) -> Result<U, Box<dyn std::error::Error>> {
        let (sc, rc): (_, oneshot::Receiver<U>) = oneshot::channel();
        self.0
            .send(Box::new(move |conn: &sqlite::Connection| {
                sc.send(cb(conn)).unwrap_or(());
            })
                as Box<dyn for<'a> FnOnce(&'a sqlite::Connection) + Send>)
            .await
            .map_err(|mpsc::error::SendError(_)| mpsc::error::SendError(()))?;
        Ok(rc.await?)
    }
}

fn main() {

mod names_database;
#[tokio::main]
async fn main() {

max_width = 80

tokio = { version = "1.15.0", features = ["macros","sync","rt"] }

tokio = { version = "1.15.0", features = ["macros","sync","rt-multi-thread"] }

[[package]]
name = "hermit-abi"
version = "0.1.19"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "62b467343b94ba476dcb2500d242dadbb39557df889310ac77c5d99100aaac33"
dependencies = [
 "libc",
]

]
[[package]]
name = "num_cpus"
version = "1.13.1"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "19e64526ebdee182341572e50e9ad03965aa510cd94427a4549448f285e957a1"
dependencies = [
 "hermit-abi",
 "libc",

 "num_cpus",