use std::{
    collections::VecDeque,
    future::Future,
    pin::Pin,
    task::{Context, Poll},
};

use actix::{
    dev::{AsyncContextParts, ContextFut, ContextParts, Envelope, Mailbox, ToEnvelope},
    fut::ActorFuture,
    Actor, ActorContext, ActorState, Addr, AsyncContext, Handler, Message, SpawnHandle,
};
use actix_web::error::Error;
use bytes::Bytes;
use futures_core::Stream;
use tokio::sync::oneshot::Sender;

/// Execution context for HTTP actors
///
/// # Example
///
/// A demonstration of [server-sent events](https://developer.mozilla.org/docs/Web/API/Server-sent_events) using actors:
///
/// ```no_run
/// use std::time::Duration;
///
/// use actix::{Actor, AsyncContext};
/// use actix_web::{get, http::header, App, HttpResponse, HttpServer};
/// use actix_web_actors::HttpContext;
/// use bytes::Bytes;
///
/// struct MyActor {
///     count: usize,
/// }
///
/// impl Actor for MyActor {
///     type Context = HttpContext<Self>;
///
///     fn started(&mut self, ctx: &mut Self::Context) {
///         ctx.run_later(Duration::from_millis(100), Self::write);
///     }
/// }
///
/// impl MyActor {
///     fn write(&mut self, ctx: &mut HttpContext<Self>) {
///         self.count += 1;
///         if self.count > 3 {
///             ctx.write_eof()
///         } else {
///             ctx.write(Bytes::from(format!("event: count\ndata: {}\n\n", self.count)));
///             ctx.run_later(Duration::from_millis(100), Self::write);
///         }
///     }
/// }
///
/// #[get("/")]
/// async fn index() -> HttpResponse {
///     HttpResponse::Ok()
///         .insert_header(header::ContentType(mime::TEXT_EVENT_STREAM))
///         .streaming(HttpContext::create(MyActor { count: 0 }))
/// }
///
/// #[actix_web::main]
/// async fn main() -> std::io::Result<()> {
///     HttpServer::new(|| App::new().service(index))
///         .bind(("127.0.0.1", 8080))?
///         .run()
///         .await
/// }
/// ```
pub struct HttpContext<A>
where
    A: Actor<Context = HttpContext<A>>,
{
    inner: ContextParts<A>,
    stream: VecDeque<Option<Bytes>>,
}

impl<A> ActorContext for HttpContext<A>
where
    A: Actor<Context = Self>,
{
    fn stop(&mut self) {
        self.inner.stop();
    }
    fn terminate(&mut self) {
        self.inner.terminate()
    }
    fn state(&self) -> ActorState {
        self.inner.state()
    }
}

impl<A> AsyncContext<A> for HttpContext<A>
where
    A: Actor<Context = Self>,
{
    #[inline]
    fn spawn<F>(&mut self, fut: F) -> SpawnHandle
    where
        F: ActorFuture<A, Output = ()> + 'static,
    {
        self.inner.spawn(fut)
    }

    #[inline]
    fn wait<F>(&mut self, fut: F)
    where
        F: ActorFuture<A, Output = ()> + 'static,
    {
        self.inner.wait(fut)
    }

    #[doc(hidden)]
    #[inline]
    fn waiting(&self) -> bool {
        self.inner.waiting()
            || self.inner.state() == ActorState::Stopping
            || self.inner.state() == ActorState::Stopped
    }

    #[inline]
    fn cancel_future(&mut self, handle: SpawnHandle) -> bool {
        self.inner.cancel_future(handle)
    }

    #[inline]
    fn address(&self) -> Addr<A> {
        self.inner.address()
    }
}

impl<A> HttpContext<A>
where
    A: Actor<Context = Self>,
{
    #[inline]
    /// Create a new HTTP Context from a request and an actor
    pub fn create(actor: A) -> impl Stream<Item = Result<Bytes, Error>> {
        let mb = Mailbox::default();
        let ctx = HttpContext {
            inner: ContextParts::new(mb.sender_producer()),
            stream: VecDeque::new(),
        };
        HttpContextFut::new(ctx, actor, mb)
    }

    /// Create a new HTTP Context
    pub fn with_factory<F>(f: F) -> impl Stream<Item = Result<Bytes, Error>>
    where
        F: FnOnce(&mut Self) -> A + 'static,
    {
        let mb = Mailbox::default();
        let mut ctx = HttpContext {
            inner: ContextParts::new(mb.sender_producer()),
            stream: VecDeque::new(),
        };

        let act = f(&mut ctx);
        HttpContextFut::new(ctx, act, mb)
    }
}

impl<A> HttpContext<A>
where
    A: Actor<Context = Self>,
{
    /// Write payload
    #[inline]
    pub fn write(&mut self, data: Bytes) {
        self.stream.push_back(Some(data));
    }

    /// Indicate end of streaming payload. Also this method calls `Self::close`.
    #[inline]
    pub fn write_eof(&mut self) {
        self.stream.push_back(None);
    }

    /// Handle of the running future
    ///
    /// SpawnHandle is the handle returned by `AsyncContext::spawn()` method.
    pub fn handle(&self) -> SpawnHandle {
        self.inner.curr_handle()
    }
}

impl<A> AsyncContextParts<A> for HttpContext<A>
where
    A: Actor<Context = Self>,
{
    fn parts(&mut self) -> &mut ContextParts<A> {
        &mut self.inner
    }
}

struct HttpContextFut<A>
where
    A: Actor<Context = HttpContext<A>>,
{
    fut: ContextFut<A, HttpContext<A>>,
}

impl<A> HttpContextFut<A>
where
    A: Actor<Context = HttpContext<A>>,
{
    fn new(ctx: HttpContext<A>, act: A, mailbox: Mailbox<A>) -> Self {
        let fut = ContextFut::new(ctx, act, mailbox);
        HttpContextFut { fut }
    }
}

impl<A> Stream for HttpContextFut<A>
where
    A: Actor<Context = HttpContext<A>>,
{
    type Item = Result<Bytes, Error>;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        if self.fut.alive() {
            let _ = Pin::new(&mut self.fut).poll(cx);
        }

        // frames
        if let Some(data) = self.fut.ctx().stream.pop_front() {
            Poll::Ready(data.map(Ok))
        } else if self.fut.alive() {
            Poll::Pending
        } else {
            Poll::Ready(None)
        }
    }
}

impl<A, M> ToEnvelope<A, M> for HttpContext<A>
where
    A: Actor<Context = HttpContext<A>> + Handler<M>,
    M: Message + Send + 'static,
    M::Result: Send,
{
    fn pack(msg: M, tx: Option<Sender<M::Result>>) -> Envelope<A> {
        Envelope::new(msg, tx)
    }
}

#[cfg(test)]
mod tests {
    use std::time::Duration;

    use actix_web::{
        http::StatusCode,
        test::{call_service, init_service, read_body, TestRequest},
        web, App, HttpResponse,
    };

    use super::*;

    struct MyActor {
        count: usize,
    }

    impl Actor for MyActor {
        type Context = HttpContext<Self>;

        fn started(&mut self, ctx: &mut Self::Context) {
            ctx.run_later(Duration::from_millis(100), Self::write);
        }
    }

    impl MyActor {
        fn write(&mut self, ctx: &mut HttpContext<Self>) {
            self.count += 1;
            if self.count > 3 {
                ctx.write_eof()
            } else {
                ctx.write(Bytes::from(format!("LINE-{}", self.count)));
                ctx.run_later(Duration::from_millis(100), Self::write);
            }
        }
    }

    #[actix_rt::test]
    async fn test_default_resource() {
        let srv = init_service(App::new().service(web::resource("/test").to(|| async {
            HttpResponse::Ok().streaming(HttpContext::create(MyActor { count: 0 }))
        })))
        .await;

        let req = TestRequest::with_uri("/test").to_request();
        let resp = call_service(&srv, req).await;
        assert_eq!(resp.status(), StatusCode::OK);

        let body = read_body(resp).await;
        assert_eq!(body, Bytes::from_static(b"LINE-1LINE-2LINE-3"));
    }
}