use std::cell::UnsafeCell;
use std::marker::PhantomData;
use std::rc::Rc;
use std::{io, mem};

use futures::unsync::oneshot;
use futures::{Async, Future, Poll, Stream};
use log::Level::Debug;

use application::Inner;
use body::{Body, BodyStream};
use context::{ActorHttpContext, Frame};
use error::Error;
use handler::{Reply, ReplyItem};
use header::ContentEncoding;
use httprequest::HttpRequest;
use httpresponse::HttpResponse;
use middleware::{Finished, Middleware, Response, Started};
use server::{HttpHandlerTask, Writer, WriterState};

#[derive(Debug, Clone, Copy)]
pub(crate) enum HandlerType {
    Normal(usize),
    Handler(usize),
    Default,
}

pub(crate) trait PipelineHandler<S> {
    fn encoding(&self) -> ContentEncoding;

    fn handle(&mut self, req: HttpRequest<S>, htype: HandlerType) -> Reply;
}

pub(crate) struct Pipeline<S, H>(PipelineInfo<S>, PipelineState<S, H>);

enum PipelineState<S, H> {
    None,
    Error,
    Starting(StartMiddlewares<S, H>),
    Handler(WaitingResponse<S, H>),
    RunMiddlewares(RunMiddlewares<S, H>),
    Response(ProcessResponse<S, H>),
    Finishing(FinishingMiddlewares<S, H>),
    Completed(Completed<S, H>),
}

impl<S: 'static, H: PipelineHandler<S>> PipelineState<S, H> {
    fn is_response(&self) -> bool {
        match *self {
            PipelineState::Response(_) => true,
            _ => false,
        }
    }

    fn poll(&mut self, info: &mut PipelineInfo<S>) -> Option<PipelineState<S, H>> {
        match *self {
            PipelineState::Starting(ref mut state) => state.poll(info),
            PipelineState::Handler(ref mut state) => state.poll(info),
            PipelineState::RunMiddlewares(ref mut state) => state.poll(info),
            PipelineState::Finishing(ref mut state) => state.poll(info),
            PipelineState::Completed(ref mut state) => state.poll(info),
            PipelineState::Response(_) | PipelineState::None | PipelineState::Error => {
                None
            }
        }
    }
}

struct PipelineInfo<S> {
    req: HttpRequest<S>,
    count: u16,
    mws: Rc<Vec<Box<Middleware<S>>>>,
    context: Option<Box<ActorHttpContext>>,
    error: Option<Error>,
    disconnected: Option<bool>,
    encoding: ContentEncoding,
}

impl<S> PipelineInfo<S> {
    fn new(req: HttpRequest<S>) -> PipelineInfo<S> {
        PipelineInfo {
            req,
            count: 0,
            mws: Rc::new(Vec::new()),
            error: None,
            context: None,
            disconnected: None,
            encoding: ContentEncoding::Auto,
        }
    }

    #[cfg_attr(feature = "cargo-clippy", allow(mut_from_ref))]
    fn req_mut(&self) -> &mut HttpRequest<S> {
        #[allow(mutable_transmutes)]
        unsafe {
            mem::transmute(&self.req)
        }
    }

    fn poll_context(&mut self) -> Poll<(), Error> {
        if let Some(ref mut context) = self.context {
            match context.poll() {
                Err(err) => Err(err),
                Ok(Async::NotReady) => Ok(Async::NotReady),
                Ok(Async::Ready(_)) => Ok(Async::Ready(())),
            }
        } else {
            Ok(Async::Ready(()))
        }
    }
}

impl<S: 'static, H: PipelineHandler<S>> Pipeline<S, H> {
    pub fn new(
        req: HttpRequest<S>, mws: Rc<Vec<Box<Middleware<S>>>>,
        handler: Rc<UnsafeCell<H>>, htype: HandlerType,
    ) -> Pipeline<S, H> {
        let mut info = PipelineInfo {
            req,
            mws,
            count: 0,
            error: None,
            context: None,
            disconnected: None,
            encoding: unsafe { &*handler.get() }.encoding(),
        };
        let state = StartMiddlewares::init(&mut info, handler, htype);

        Pipeline(info, state)
    }
}

impl Pipeline<(), Inner<()>> {
    pub fn error<R: Into<HttpResponse>>(err: R) -> Box<HttpHandlerTask> {
        Box::new(Pipeline::<(), Inner<()>>(
            PipelineInfo::new(HttpRequest::default()),
            ProcessResponse::init(err.into()),
        ))
    }
}

impl<S: 'static, H> Pipeline<S, H> {
    fn is_done(&self) -> bool {
        match self.1 {
            PipelineState::None
            | PipelineState::Error
            | PipelineState::Starting(_)
            | PipelineState::Handler(_)
            | PipelineState::RunMiddlewares(_)
            | PipelineState::Response(_) => true,
            PipelineState::Finishing(_) | PipelineState::Completed(_) => false,
        }
    }
}

impl<S: 'static, H: PipelineHandler<S>> HttpHandlerTask for Pipeline<S, H> {
    fn disconnected(&mut self) {
        self.0.disconnected = Some(true);
    }

    fn poll_io(&mut self, io: &mut Writer) -> Poll<bool, Error> {
        let info: &mut PipelineInfo<_> = unsafe { mem::transmute(&mut self.0) };

        loop {
            if self.1.is_response() {
                let state = mem::replace(&mut self.1, PipelineState::None);
                if let PipelineState::Response(st) = state {
                    match st.poll_io(io, info) {
                        Ok(state) => {
                            self.1 = state;
                            if let Some(error) = self.0.error.take() {
                                return Err(error);
                            } else {
                                return Ok(Async::Ready(self.is_done()));
                            }
                        }
                        Err(state) => {
                            self.1 = state;
                            return Ok(Async::NotReady);
                        }
                    }
                }
            }
            match self.1 {
                PipelineState::None => return Ok(Async::Ready(true)),
                PipelineState::Error => {
                    return Err(io::Error::new(io::ErrorKind::Other, "Internal error").into())
                }
                _ => (),
            }

            match self.1.poll(info) {
                Some(state) => self.1 = state,
                None => return Ok(Async::NotReady),
            }
        }
    }

    fn poll(&mut self) -> Poll<(), Error> {
        let info: &mut PipelineInfo<_> = unsafe { mem::transmute(&mut self.0) };

        loop {
            match self.1 {
                PipelineState::None | PipelineState::Error => {
                    return Ok(Async::Ready(()))
                }
                _ => (),
            }

            if let Some(state) = self.1.poll(info) {
                self.1 = state;
            } else {
                return Ok(Async::NotReady);
            }
        }
    }
}

type Fut = Box<Future<Item = Option<HttpResponse>, Error = Error>>;

/// Middlewares start executor
struct StartMiddlewares<S, H> {
    hnd: Rc<UnsafeCell<H>>,
    htype: HandlerType,
    fut: Option<Fut>,
    _s: PhantomData<S>,
}

impl<S: 'static, H: PipelineHandler<S>> StartMiddlewares<S, H> {
    fn init(
        info: &mut PipelineInfo<S>, hnd: Rc<UnsafeCell<H>>, htype: HandlerType
    ) -> PipelineState<S, H> {
        // execute middlewares, we need this stage because middlewares could be
        // non-async and we can move to next state immediately
        let len = info.mws.len() as u16;
        loop {
            if info.count == len {
                let reply = unsafe { &mut *hnd.get() }.handle(info.req.clone(), htype);
                return WaitingResponse::init(info, reply);
            } else {
                match info.mws[info.count as usize].start(&mut info.req) {
                    Ok(Started::Done) => info.count += 1,
                    Ok(Started::Response(resp)) => {
                        return RunMiddlewares::init(info, resp)
                    }
                    Ok(Started::Future(mut fut)) => match fut.poll() {
                        Ok(Async::NotReady) => {
                            return PipelineState::Starting(StartMiddlewares {
                                hnd,
                                htype,
                                fut: Some(fut),
                                _s: PhantomData,
                            })
                        }
                        Ok(Async::Ready(resp)) => {
                            if let Some(resp) = resp {
                                return RunMiddlewares::init(info, resp);
                            }
                            info.count += 1;
                        }
                        Err(err) => return ProcessResponse::init(err.into()),
                    },
                    Err(err) => return ProcessResponse::init(err.into()),
                }
            }
        }
    }

    fn poll(&mut self, info: &mut PipelineInfo<S>) -> Option<PipelineState<S, H>> {
        let len = info.mws.len() as u16;
        'outer: loop {
            match self.fut.as_mut().unwrap().poll() {
                Ok(Async::NotReady) => return None,
                Ok(Async::Ready(resp)) => {
                    info.count += 1;
                    if let Some(resp) = resp {
                        return Some(RunMiddlewares::init(info, resp));
                    }
                    if info.count == len {
                        let reply = unsafe { &mut *self.hnd.get() }
                            .handle(info.req.clone(), self.htype);
                        return Some(WaitingResponse::init(info, reply));
                    } else {
                        loop {
                            match info.mws[info.count as usize].start(info.req_mut()) {
                                Ok(Started::Done) => info.count += 1,
                                Ok(Started::Response(resp)) => {
                                    return Some(RunMiddlewares::init(info, resp));
                                }
                                Ok(Started::Future(fut)) => {
                                    self.fut = Some(fut);
                                    continue 'outer;
                                }
                                Err(err) => {
                                    return Some(ProcessResponse::init(err.into()))
                                }
                            }
                        }
                    }
                }
                Err(err) => return Some(ProcessResponse::init(err.into())),
            }
        }
    }
}

// waiting for response
struct WaitingResponse<S, H> {
    fut: Box<Future<Item = HttpResponse, Error = Error>>,
    _s: PhantomData<S>,
    _h: PhantomData<H>,
}

impl<S: 'static, H> WaitingResponse<S, H> {
    #[inline]
    fn init(info: &mut PipelineInfo<S>, reply: Reply) -> PipelineState<S, H> {
        match reply.into() {
            ReplyItem::Message(resp) => RunMiddlewares::init(info, resp),
            ReplyItem::Future(fut) => PipelineState::Handler(WaitingResponse {
                fut,
                _s: PhantomData,
                _h: PhantomData,
            }),
        }
    }

    fn poll(&mut self, info: &mut PipelineInfo<S>) -> Option<PipelineState<S, H>> {
        match self.fut.poll() {
            Ok(Async::NotReady) => None,
            Ok(Async::Ready(response)) => Some(RunMiddlewares::init(info, response)),
            Err(err) => Some(ProcessResponse::init(err.into())),
        }
    }
}

/// Middlewares response executor
struct RunMiddlewares<S, H> {
    curr: usize,
    fut: Option<Box<Future<Item = HttpResponse, Error = Error>>>,
    _s: PhantomData<S>,
    _h: PhantomData<H>,
}

impl<S: 'static, H> RunMiddlewares<S, H> {
    fn init(info: &mut PipelineInfo<S>, mut resp: HttpResponse) -> PipelineState<S, H> {
        if info.count == 0 {
            return ProcessResponse::init(resp);
        }
        let mut curr = 0;
        let len = info.mws.len();

        loop {
            resp = match info.mws[curr].response(info.req_mut(), resp) {
                Err(err) => {
                    info.count = (curr + 1) as u16;
                    return ProcessResponse::init(err.into());
                }
                Ok(Response::Done(r)) => {
                    curr += 1;
                    if curr == len {
                        return ProcessResponse::init(r);
                    } else {
                        r
                    }
                }
                Ok(Response::Future(fut)) => {
                    return PipelineState::RunMiddlewares(RunMiddlewares {
                        curr,
                        fut: Some(fut),
                        _s: PhantomData,
                        _h: PhantomData,
                    })
                }
            };
        }
    }

    fn poll(&mut self, info: &mut PipelineInfo<S>) -> Option<PipelineState<S, H>> {
        let len = info.mws.len();

        loop {
            // poll latest fut
            let mut resp = match self.fut.as_mut().unwrap().poll() {
                Ok(Async::NotReady) => return None,
                Ok(Async::Ready(resp)) => {
                    self.curr += 1;
                    resp
                }
                Err(err) => return Some(ProcessResponse::init(err.into())),
            };

            loop {
                if self.curr == len {
                    return Some(ProcessResponse::init(resp));
                } else {
                    match info.mws[self.curr].response(info.req_mut(), resp) {
                        Err(err) => return Some(ProcessResponse::init(err.into())),
                        Ok(Response::Done(r)) => {
                            self.curr += 1;
                            resp = r
                        }
                        Ok(Response::Future(fut)) => {
                            self.fut = Some(fut);
                            break;
                        }
                    }
                }
            }
        }
    }
}

struct ProcessResponse<S, H> {
    resp: HttpResponse,
    iostate: IOState,
    running: RunningState,
    drain: Option<oneshot::Sender<()>>,
    _s: PhantomData<S>,
    _h: PhantomData<H>,
}

#[derive(PartialEq)]
enum RunningState {
    Running,
    Paused,
    Done,
}

impl RunningState {
    #[inline]
    fn pause(&mut self) {
        if *self != RunningState::Done {
            *self = RunningState::Paused
        }
    }
    #[inline]
    fn resume(&mut self) {
        if *self != RunningState::Done {
            *self = RunningState::Running
        }
    }
}

enum IOState {
    Response,
    Payload(BodyStream),
    Actor(Box<ActorHttpContext>),
    Done,
}

impl<S: 'static, H> ProcessResponse<S, H> {
    #[inline]
    fn init(resp: HttpResponse) -> PipelineState<S, H> {
        PipelineState::Response(ProcessResponse {
            resp,
            iostate: IOState::Response,
            running: RunningState::Running,
            drain: None,
            _s: PhantomData,
            _h: PhantomData,
        })
    }

    fn poll_io(
        mut self, io: &mut Writer, info: &mut PipelineInfo<S>
    ) -> Result<PipelineState<S, H>, PipelineState<S, H>> {
        loop {
            if self.drain.is_none() && self.running != RunningState::Paused {
                // if task is paused, write buffer is probably full
                'inner: loop {
                    let result = match mem::replace(&mut self.iostate, IOState::Done) {
                        IOState::Response => {
                            let encoding =
                                self.resp.content_encoding().unwrap_or(info.encoding);

                            let result = match io.start(
                                info.req_mut().get_inner(),
                                &mut self.resp,
                                encoding,
                            ) {
                                Ok(res) => res,
                                Err(err) => {
                                    info.error = Some(err.into());
                                    return Ok(FinishingMiddlewares::init(
                                        info,
                                        self.resp,
                                    ));
                                }
                            };

                            if let Some(err) = self.resp.error() {
                                if self.resp.status().is_server_error() {
                                    error!(
                                        "Error occured during request handling: {}",
                                        err
                                    );
                                } else {
                                    warn!(
                                        "Error occured during request handling: {}",
                                        err
                                    );
                                }
                                if log_enabled!(Debug) {
                                    debug!("{:?}", err);
                                }
                            }

                            // always poll stream or actor for the first time
                            match self.resp.replace_body(Body::Empty) {
                                Body::Streaming(stream) => {
                                    self.iostate = IOState::Payload(stream);
                                    continue 'inner;
                                }
                                Body::Actor(ctx) => {
                                    self.iostate = IOState::Actor(ctx);
                                    continue 'inner;
                                }
                                _ => (),
                            }

                            result
                        }
                        IOState::Payload(mut body) => match body.poll() {
                            Ok(Async::Ready(None)) => {
                                if let Err(err) = io.write_eof() {
                                    info.error = Some(err.into());
                                    return Ok(FinishingMiddlewares::init(
                                        info,
                                        self.resp,
                                    ));
                                }
                                break;
                            }
                            Ok(Async::Ready(Some(chunk))) => {
                                self.iostate = IOState::Payload(body);
                                match io.write(chunk.into()) {
                                    Err(err) => {
                                        info.error = Some(err.into());
                                        return Ok(FinishingMiddlewares::init(
                                            info,
                                            self.resp,
                                        ));
                                    }
                                    Ok(result) => result,
                                }
                            }
                            Ok(Async::NotReady) => {
                                self.iostate = IOState::Payload(body);
                                break;
                            }
                            Err(err) => {
                                info.error = Some(err);
                                return Ok(FinishingMiddlewares::init(info, self.resp));
                            }
                        },
                        IOState::Actor(mut ctx) => {
                            if info.disconnected.take().is_some() {
                                ctx.disconnected();
                            }
                            match ctx.poll() {
                                Ok(Async::Ready(Some(vec))) => {
                                    if vec.is_empty() {
                                        self.iostate = IOState::Actor(ctx);
                                        break;
                                    }
                                    let mut res = None;
                                    for frame in vec {
                                        match frame {
                                            Frame::Chunk(None) => {
                                                info.context = Some(ctx);
                                                if let Err(err) = io.write_eof() {
                                                    info.error = Some(err.into());
                                                    return Ok(
                                                        FinishingMiddlewares::init(
                                                            info,
                                                            self.resp,
                                                        ),
                                                    );
                                                }
                                                break 'inner;
                                            }
                                            Frame::Chunk(Some(chunk)) => {
                                                match io.write(chunk) {
                                                    Err(err) => {
                                                        info.error = Some(err.into());
                                                        return Ok(
                                                            FinishingMiddlewares::init(
                                                                info,
                                                                self.resp,
                                                            ),
                                                        );
                                                    }
                                                    Ok(result) => res = Some(result),
                                                }
                                            }
                                            Frame::Drain(fut) => self.drain = Some(fut),
                                        }
                                    }
                                    self.iostate = IOState::Actor(ctx);
                                    if self.drain.is_some() {
                                        self.running.resume();
                                        break 'inner;
                                    }
                                    res.unwrap()
                                }
                                Ok(Async::Ready(None)) => break,
                                Ok(Async::NotReady) => {
                                    self.iostate = IOState::Actor(ctx);
                                    break;
                                }
                                Err(err) => {
                                    info.error = Some(err);
                                    return Ok(FinishingMiddlewares::init(
                                        info,
                                        self.resp,
                                    ));
                                }
                            }
                        }
                        IOState::Done => break,
                    };

                    match result {
                        WriterState::Pause => {
                            self.running.pause();
                            break;
                        }
                        WriterState::Done => self.running.resume(),
                    }
                }
            }

            // flush io but only if we need to
            if self.running == RunningState::Paused || self.drain.is_some() {
                match io.poll_completed(false) {
                    Ok(Async::Ready(_)) => {
                        self.running.resume();

                        // resolve drain futures
                        if let Some(tx) = self.drain.take() {
                            let _ = tx.send(());
                        }
                        // restart io processing
                        continue;
                    }
                    Ok(Async::NotReady) => return Err(PipelineState::Response(self)),
                    Err(err) => {
                        info.error = Some(err.into());
                        return Ok(FinishingMiddlewares::init(info, self.resp));
                    }
                }
            }
            break;
        }

        // response is completed
        match self.iostate {
            IOState::Done => {
                match io.write_eof() {
                    Ok(_) => (),
                    Err(err) => {
                        info.error = Some(err.into());
                        return Ok(FinishingMiddlewares::init(info, self.resp));
                    }
                }
                self.resp.set_response_size(io.written());
                Ok(FinishingMiddlewares::init(info, self.resp))
            }
            _ => Err(PipelineState::Response(self)),
        }
    }
}

/// Middlewares start executor
struct FinishingMiddlewares<S, H> {
    resp: HttpResponse,
    fut: Option<Box<Future<Item = (), Error = Error>>>,
    _s: PhantomData<S>,
    _h: PhantomData<H>,
}

impl<S: 'static, H> FinishingMiddlewares<S, H> {
    fn init(info: &mut PipelineInfo<S>, resp: HttpResponse) -> PipelineState<S, H> {
        if info.count == 0 {
            Completed::init(info)
        } else {
            let mut state = FinishingMiddlewares {
                resp,
                fut: None,
                _s: PhantomData,
                _h: PhantomData,
            };
            if let Some(st) = state.poll(info) {
                st
            } else {
                PipelineState::Finishing(state)
            }
        }
    }

    fn poll(&mut self, info: &mut PipelineInfo<S>) -> Option<PipelineState<S, H>> {
        loop {
            // poll latest fut
            let not_ready = if let Some(ref mut fut) = self.fut {
                match fut.poll() {
                    Ok(Async::NotReady) => true,
                    Ok(Async::Ready(())) => false,
                    Err(err) => {
                        error!("Middleware finish error: {}", err);
                        false
                    }
                }
            } else {
                false
            };
            if not_ready {
                return None;
            }
            self.fut = None;
            info.count -= 1;

            match info.mws[info.count as usize].finish(info.req_mut(), &self.resp) {
                Finished::Done => {
                    if info.count == 0 {
                        return Some(Completed::init(info));
                    }
                }
                Finished::Future(fut) => {
                    self.fut = Some(fut);
                }
            }
        }
    }
}

#[derive(Debug)]
struct Completed<S, H>(PhantomData<S>, PhantomData<H>);

impl<S, H> Completed<S, H> {
    #[inline]
    fn init(info: &mut PipelineInfo<S>) -> PipelineState<S, H> {
        if let Some(ref err) = info.error {
            error!("Error occurred during request handling: {}", err);
        }

        if info.context.is_none() {
            PipelineState::None
        } else {
            PipelineState::Completed(Completed(PhantomData, PhantomData))
        }
    }

    #[inline]
    fn poll(&mut self, info: &mut PipelineInfo<S>) -> Option<PipelineState<S, H>> {
        match info.poll_context() {
            Ok(Async::NotReady) => None,
            Ok(Async::Ready(())) => Some(PipelineState::None),
            Err(_) => Some(PipelineState::Error),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use actix::*;
    use context::HttpContext;
    use futures::future::{lazy, result};
    use tokio_core::reactor::Core;

    impl<S, H> PipelineState<S, H> {
        fn is_none(&self) -> Option<bool> {
            if let PipelineState::None = *self {
                Some(true)
            } else {
                None
            }
        }
        fn completed(self) -> Option<Completed<S, H>> {
            if let PipelineState::Completed(c) = self {
                Some(c)
            } else {
                None
            }
        }
    }

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

    #[test]
    fn test_completed() {
        Core::new()
            .unwrap()
            .run(lazy(|| {
                let mut info = PipelineInfo::new(HttpRequest::default());
                Completed::<(), Inner<()>>::init(&mut info)
                    .is_none()
                    .unwrap();

                let req = HttpRequest::default();
                let mut ctx = HttpContext::new(req.clone(), MyActor);
                let addr: Addr<Unsync, _> = ctx.address();
                let mut info = PipelineInfo::new(req);
                info.context = Some(Box::new(ctx));
                let mut state = Completed::<(), Inner<()>>::init(&mut info)
                    .completed()
                    .unwrap();

                assert!(state.poll(&mut info).is_none());
                let pp = Pipeline(info, PipelineState::Completed(state));
                assert!(!pp.is_done());

                let Pipeline(mut info, st) = pp;
                let mut st = st.completed().unwrap();
                drop(addr);

                assert!(st.poll(&mut info).unwrap().is_none().unwrap());

                result(Ok::<_, ()>(()))
            }))
            .unwrap();
    }
}