use std::future::Future;
use std::pin::Pin;
use std::task::{self, Poll};

use futures::io::{AsyncRead, AsyncWrite};
use imap_codec::types::core::Tag;
use tokio_tower::pipeline::Server as PipelineServer;
use tower::Service;

use super::pipeline::Connection;
use super::Imap;
use crate::proto::{Request, Response};

pub struct Connecting<C, F, S>
where
    C: AsyncRead + AsyncWrite + Unpin,
    S: Service<Request, Response = Response>,
    S::Future: Send + 'static,
{
    pub state: Option<ConnectingState<C, F, S>>,
    pub protocol: Imap,
}

pub enum ConnectingState<C, F, S>
where
    C: AsyncRead + AsyncWrite + Unpin,
    S: Service<Request, Response = Response>,
    S::Future: Send + 'static,
{
    Waiting {
        conn: Connection<C>,
        service_fut: F,
    },
    Ready {
        conn: Connection<C>,
        service: S,
    },
    Serving {
        server: PipelineServer<Connection<C>, PipelineService<S>>,
    },
    Finished,
}

impl<C, F, ME, S> ConnectingState<C, F, S>
where
    C: AsyncRead + AsyncWrite + Unpin,
    F: Future<Output = std::result::Result<S, ME>> + Unpin,
    ME: std::fmt::Display,
    S: Service<Request, Response = Response>,
    S::Future: Send + 'static,
    S::Error: std::fmt::Display,
{
    fn poll_new_state(self, cx: &mut task::Context) -> (Self, Option<Poll<()>>) {
        match self {
            ConnectingState::Waiting {
                conn,
                mut service_fut,
            } => {
                let service = match Pin::new(&mut service_fut).poll(cx) {
                    Poll::Ready(Ok(service)) => service,
                    Poll::Ready(Err(err)) => {
                        tracing::error!("Connection error: {}", err);
                        return (
                            ConnectingState::Waiting { conn, service_fut },
                            Some(Poll::Ready(())),
                        );
                    }
                    Poll::Pending => {
                        return (
                            ConnectingState::Waiting { conn, service_fut },
                            Some(Poll::Pending),
                        )
                    }
                };

                let mut conn = conn;

                // TODO: Properly handle server greeting
                {
                    use futures::SinkExt;

                    let greeting = Response::ok("Hello").unwrap(); // "Hello" is a valid
                                                                   // greeting
                    conn.start_send_unpin((None, greeting)).unwrap();
                }

                (ConnectingState::Ready { conn, service }, None)
            }
            ConnectingState::Ready { conn, service } => (
                ConnectingState::Serving {
                    server: PipelineServer::new(conn, PipelineService { inner: service }),
                },
                None,
            ),
            ConnectingState::Serving { mut server } => match Pin::new(&mut server).poll(cx) {
                Poll::Ready(Ok(_)) => (ConnectingState::Finished, Some(Poll::Ready(()))),
                Poll::Ready(Err(err)) => {
                    tracing::debug!("Connecting error: {}", err);
                    (ConnectingState::Finished, Some(Poll::Ready(())))
                }
                Poll::Pending => (ConnectingState::Serving { server }, Some(Poll::Pending)),
            },
            ConnectingState::Finished => (self, Some(Poll::Ready(()))),
        }
    }
}

impl<C, F, ME, S> Future for Connecting<C, F, S>
where
    C: AsyncRead + AsyncWrite + Unpin,
    F: Future<Output = std::result::Result<S, ME>> + Unpin,
    ME: std::fmt::Display,
    S: Service<Request, Response = Response>,
    S::Future: Send + 'static,
    S::Error: std::fmt::Display,
{
    type Output = ();

    fn poll(mut self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
        loop {
            let state = self.as_mut().state.take().unwrap();
            let (next, res) = state.poll_new_state(cx);

            self.state = Some(next);
            if let Some(res) = res {
                return res;
            }
        }
    }
}

impl<C, F, S> Unpin for Connecting<C, F, S>
where
    C: AsyncRead + AsyncWrite + Unpin,
    S: Service<Request, Response = Response>,
    S::Future: Send + 'static,
{
}

pub struct PipelineService<S> {
    inner: S,
}

impl<S> Service<Request> for PipelineService<S>
where
    S: Service<Request>,
    S::Future: Send + 'static,
{
    type Response = (Option<Tag>, S::Response);
    type Error = S::Error;
    type Future = futures::future::BoxFuture<'static, Result<Self::Response, Self::Error>>;

    fn poll_ready(&mut self, cx: &mut task::Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.inner.poll_ready(cx)
    }

    fn call(&mut self, req: Request) -> Self::Future {
        use futures::{FutureExt, TryFutureExt};

        let tag = req.command.tag.clone();

        self.inner.call(req).map_ok(|res| (Some(tag), res)).boxed()
    }
}