//! synchronous function as middleware.

use core::mem;

use std::sync::mpsc::Receiver;

use tokio::sync::mpsc::UnboundedSender;

use crate::{
    context::WebContext,
    http::{Request, RequestExt, Response},
    service::Service,
};

/// experimental type for sync function as middleware.
pub struct SyncMiddleware<F>(F);

impl<F> SyncMiddleware<F> {
    /// *. Sync middleware does not have access to request/response body.
    ///
    /// construct a new middleware with given sync function.
    /// the function must be actively calling [Next::call] and finish it to drive inner services to completion.
    /// panic in sync function middleware would result in a panic at task level and it's client connection would
    /// be terminated immediately.
    pub fn new<C, E>(func: F) -> Self
    where
        F: Fn(&mut Next<E>, WebContext<'_, C>) -> Result<Response<()>, E> + Send + Sync + 'static,
        C: Clone + Send + 'static,
        E: Send + 'static,
    {
        Self(func)
    }
}

/// next/inner services of a middleware function. [Next::call] must run to complete in order to drive
/// services.
pub struct Next<E> {
    tx: UnboundedSender<Request<RequestExt<()>>>,
    rx: Receiver<Result<Response<()>, E>>,
}

impl<E> Next<E> {
    /// call next/inner services to complete where they would produce either a http response or an error.
    pub fn call<C>(&mut self, mut ctx: WebContext<'_, C>) -> Result<Response<()>, E> {
        let req = mem::take(ctx.req_mut());
        self.tx.send(req).unwrap();
        self.rx.recv().unwrap()
    }
}

impl<F, S, E> Service<Result<S, E>> for SyncMiddleware<F>
where
    F: Clone,
{
    type Response = service::SyncService<F, S>;
    type Error = E;

    async fn call(&self, res: Result<S, E>) -> Result<Self::Response, Self::Error> {
        res.map(|service| service::SyncService {
            func: self.0.clone(),
            service,
        })
    }
}

mod service {
    use core::cell::RefCell;

    use std::sync::mpsc::sync_channel;

    use tokio::sync::mpsc::unbounded_channel;

    use crate::{body::RequestBody, http::WebResponse, service::ready::ReadyService};

    use super::*;

    pub struct SyncService<F, S> {
        pub(super) func: F,
        pub(super) service: S,
    }

    impl<'r, F, C, S, B, ResB, Err> Service<WebContext<'r, C, B>> for SyncService<F, S>
    where
        F: Fn(&mut Next<Err>, WebContext<'_, C>) -> Result<Response<()>, Err> + Send + Clone + 'static,
        C: Clone + Send + 'static,
        S: for<'r2> Service<WebContext<'r, C, B>, Response = WebResponse<ResB>, Error = Err>,
        Err: Send + 'static,
    {
        type Response = WebResponse<ResB>;
        type Error = Err;

        async fn call(&self, mut ctx: WebContext<'r, C, B>) -> Result<Self::Response, Self::Error> {
            let func = self.func.clone();
            let state = ctx.state().clone();
            let mut req = mem::take(ctx.req_mut());

            let (tx, mut rx) = unbounded_channel();
            let (tx2, rx2) = sync_channel(1);

            let mut next = Next { tx, rx: rx2 };
            let handle = tokio::task::spawn_blocking(move || {
                let mut body = RefCell::new(RequestBody::None);
                let ctx = WebContext::new(&mut req, &mut body, &state);
                func(&mut next, ctx)
            });

            *ctx.req_mut() = match rx.recv().await {
                Some(req) => req,
                None => {
                    // tx is dropped which means spawned thread exited already. join it and panic if necessary.
                    match handle.await.unwrap() {
                        Ok(_) => todo!("there is no support for body type yet"),
                        Err(e) => return Err(e),
                    }
                }
            };

            match self.service.call(ctx).await {
                Ok(res) => {
                    let (parts, body) = res.into_parts();
                    let _ = tx2.send(Ok(Response::from_parts(parts, ())));
                    let res = handle.await.unwrap()?;
                    Ok(res.map(|_| body))
                }
                Err(e) => {
                    let _ = tx2.send(Err(e));
                    let res = handle.await.unwrap()?;
                    Ok(res.map(|_| todo!("there is no support for body type yet")))
                }
            }
        }
    }

    impl<F, S> ReadyService for SyncService<F, S>
    where
        S: ReadyService,
    {
        type Ready = S::Ready;

        #[inline]
        async fn ready(&self) -> Self::Ready {
            self.service.ready().await
        }
    }
}

#[cfg(test)]
mod test {
    use core::convert::Infallible;

    use crate::{
        body::ResponseBody,
        http::{StatusCode, WebResponse},
        service::fn_service,
        App,
    };

    use super::*;

    async fn handler(req: WebContext<'_, &'static str>) -> Result<WebResponse, Infallible> {
        assert_eq!(*req.state(), "996");
        Ok(req.into_response(ResponseBody::empty()))
    }

    fn middleware<E>(next: &mut Next<E>, ctx: WebContext<'_, &'static str>) -> Result<Response<()>, E> {
        next.call(ctx)
    }

    #[tokio::test]
    async fn sync_middleware() {
        let res = App::new()
            .with_state("996")
            .at("/", fn_service(handler))
            .enclosed(SyncMiddleware::new(middleware))
            .finish()
            .call(())
            .await
            .unwrap()
            .call(Request::default())
            .await
            .unwrap();

        assert_eq!(res.status(), StatusCode::OK);
    }
}