use std::{io, cmp, mem};
use std::rc::Rc;
use std::io::{Read, Write};
use std::time::Duration;
use std::net::SocketAddr;
use std::collections::VecDeque;

use actix::Arbiter;
use http::request::Parts;
use http2::{Reason, RecvStream};
use http2::server::{self, Connection, Handshake, SendResponse};
use bytes::{Buf, Bytes};
use futures::{Async, Poll, Future, Stream};
use tokio_io::{AsyncRead, AsyncWrite};
use tokio_core::reactor::Timeout;

use pipeline::Pipeline;
use h2writer::H2Writer;
use worker::WorkerSettings;
use channel::{HttpHandler, HttpHandlerTask};
use error::PayloadError;
use encoding::PayloadType;
use httpcodes::HTTPNotFound;
use httprequest::HttpRequest;
use payload::{Payload, PayloadWriter};

bitflags! {
    struct Flags: u8 {
        const DISCONNECTED = 0b0000_0010;
    }
}

/// HTTP/2 Transport
pub(crate) struct Http2<T, H>
    where T: AsyncRead + AsyncWrite + 'static, H: 'static
{
    flags: Flags,
    settings: Rc<WorkerSettings<H>>,
    addr: Option<SocketAddr>,
    state: State<IoWrapper<T>>,
    tasks: VecDeque<Entry>,
    keepalive_timer: Option<Timeout>,
}

enum State<T: AsyncRead + AsyncWrite> {
    Handshake(Handshake<T, Bytes>),
    Server(Connection<T, Bytes>),
    Empty,
}

impl<T, H> Http2<T, H>
    where T: AsyncRead + AsyncWrite + 'static,
          H: HttpHandler + 'static
{
    pub fn new(h: Rc<WorkerSettings<H>>, io: T, addr: Option<SocketAddr>, buf: Bytes) -> Self
    {
        Http2{ flags: Flags::empty(),
               settings: h,
               addr: addr,
               tasks: VecDeque::new(),
               state: State::Handshake(
                   server::handshake(IoWrapper{unread: Some(buf), inner: io})),
               keepalive_timer: None,
        }
    }

    pub(crate) fn shutdown(&mut self) {
        self.state = State::Empty;
        self.tasks.clear();
        self.keepalive_timer.take();
    }

    pub fn settings(&self) -> &WorkerSettings<H> {
        self.settings.as_ref()
    }

    pub fn poll(&mut self) -> Poll<(), ()> {
        // server
        if let State::Server(ref mut server) = self.state {
            // keep-alive timer
            if let Some(ref mut timeout) = self.keepalive_timer {
                match timeout.poll() {
                    Ok(Async::Ready(_)) => {
                        trace!("Keep-alive timeout, close connection");
                        return Ok(Async::Ready(()))
                    }
                    Ok(Async::NotReady) => (),
                    Err(_) => unreachable!(),
                }
            }

            loop {
                let mut not_ready = true;

                // check in-flight connections
                for item in &mut self.tasks {
                    // read payload
                    item.poll_payload();

                    if !item.flags.contains(EntryFlags::EOF) {
                        match item.task.poll_io(&mut item.stream) {
                            Ok(Async::Ready(ready)) => {
                                item.flags.insert(EntryFlags::EOF);
                                if ready {
                                    item.flags.insert(EntryFlags::FINISHED);
                                }
                                not_ready = false;
                            },
                            Ok(Async::NotReady) => (),
                            Err(err) => {
                                error!("Unhandled error: {}", err);
                                item.flags.insert(EntryFlags::EOF);
                                item.flags.insert(EntryFlags::ERROR);
                                item.stream.reset(Reason::INTERNAL_ERROR);
                            }
                        }
                    } else if !item.flags.contains(EntryFlags::FINISHED) {
                        match item.task.poll() {
                            Ok(Async::NotReady) => (),
                            Ok(Async::Ready(_)) => {
                                not_ready = false;
                                item.flags.insert(EntryFlags::FINISHED);
                            },
                            Err(err) => {
                                item.flags.insert(EntryFlags::ERROR);
                                item.flags.insert(EntryFlags::FINISHED);
                                error!("Unhandled error: {}", err);
                            }
                        }
                    }
                }

                // cleanup finished tasks
                while !self.tasks.is_empty() {
                    if self.tasks[0].flags.contains(EntryFlags::EOF) &&
                        self.tasks[0].flags.contains(EntryFlags::FINISHED) ||
                        self.tasks[0].flags.contains(EntryFlags::ERROR)
                    {
                        self.tasks.pop_front();
                    } else {
                        break
                    }
                }

                // get request
                if !self.flags.contains(Flags::DISCONNECTED) {
                    match server.poll() {
                        Ok(Async::Ready(None)) => {
                            not_ready = false;
                            self.flags.insert(Flags::DISCONNECTED);
                            for entry in &mut self.tasks {
                                entry.task.disconnected()
                            }
                        },
                        Ok(Async::Ready(Some((req, resp)))) => {
                            not_ready = false;
                            let (parts, body) = req.into_parts();

                            // stop keepalive timer
                            self.keepalive_timer.take();

                            self.tasks.push_back(
                                Entry::new(parts, body, resp, self.addr, &self.settings));
                        }
                        Ok(Async::NotReady) => {
                            // start keep-alive timer
                            if self.tasks.is_empty() {
                                if self.settings.keep_alive_enabled() {
                                    let keep_alive = self.settings.keep_alive();
                                    if keep_alive > 0 && self.keepalive_timer.is_none() {
                                        trace!("Start keep-alive timer");
                                        let mut timeout = Timeout::new(
                                            Duration::new(keep_alive, 0),
                                            Arbiter::handle()).unwrap();
                                        // register timeout
                                        let _ = timeout.poll();
                                        self.keepalive_timer = Some(timeout);
                                    }
                                } else {
                                    // keep-alive disable, drop connection
                                    return Ok(Async::Ready(()))
                                }
                            } else {
                                // keep-alive unset, rely on operating system
                                return Ok(Async::NotReady)
                            }
                        }
                        Err(err) => {
                            trace!("Connection error: {}", err);
                            self.flags.insert(Flags::DISCONNECTED);
                            for entry in &mut self.tasks {
                                entry.task.disconnected()
                            }
                            self.keepalive_timer.take();
                        },
                    }
                }

                if not_ready {
                    if self.tasks.is_empty() && self.flags.contains(Flags::DISCONNECTED) {
                        return Ok(Async::Ready(()))
                    } else {
                        return Ok(Async::NotReady)
                    }
                }
            }
        }

        // handshake
        self.state = if let State::Handshake(ref mut handshake) = self.state {
            match handshake.poll() {
                Ok(Async::Ready(srv)) => {
                    State::Server(srv)
                },
                Ok(Async::NotReady) =>
                    return Ok(Async::NotReady),
                Err(err) => {
                    trace!("Error handling connection: {}", err);
                    return Err(())
                }
            }
        } else {
            mem::replace(&mut self.state, State::Empty)
        };

        self.poll()
    }
}

bitflags! {
    struct EntryFlags: u8 {
        const EOF = 0b0000_0001;
        const REOF = 0b0000_0010;
        const ERROR = 0b0000_0100;
        const FINISHED = 0b0000_1000;
    }
}

struct Entry {
    task: Box<HttpHandlerTask>,
    payload: PayloadType,
    recv: RecvStream,
    stream: H2Writer,
    capacity: usize,
    flags: EntryFlags,
}

impl Entry {
    fn new<H>(parts: Parts,
              recv: RecvStream,
              resp: SendResponse<Bytes>,
              addr: Option<SocketAddr>,
              settings: &Rc<WorkerSettings<H>>) -> Entry
        where H: HttpHandler + 'static
    {
        // Payload and Content-Encoding
        let (psender, payload) = Payload::new(false);

        let msg = settings.get_http_message();
        msg.get_mut().uri = parts.uri;
        msg.get_mut().method = parts.method;
        msg.get_mut().version = parts.version;
        msg.get_mut().headers = parts.headers;
        msg.get_mut().payload = Some(payload);
        msg.get_mut().addr = addr;

        let mut req = HttpRequest::from_message(msg);

        // Payload sender
        let psender = PayloadType::new(req.headers(), psender);

        // start request processing
        let mut task = None;
        for h in settings.handlers().iter_mut() {
            req = match h.handle(req) {
                Ok(t) => {
                    task = Some(t);
                    break
                },
                Err(req) => req,
            }
        }

        Entry {task: task.unwrap_or_else(|| Pipeline::error(HTTPNotFound)),
               payload: psender,
               recv: recv,
               stream: H2Writer::new(resp, settings.get_shared_bytes()),
               flags: EntryFlags::empty(),
               capacity: 0,
        }
    }

    fn poll_payload(&mut self) {
        if !self.flags.contains(EntryFlags::REOF) {
            match self.recv.poll() {
                Ok(Async::Ready(Some(chunk))) => {
                    self.payload.feed_data(chunk);
                },
                Ok(Async::Ready(None)) => {
                    self.flags.insert(EntryFlags::REOF);
                },
                Ok(Async::NotReady) => (),
                Err(err) => {
                    self.payload.set_error(PayloadError::Http2(err))
                }
            }

            let capacity = self.payload.capacity();
            if self.capacity != capacity {
                self.capacity = capacity;
                if let Err(err) = self.recv.release_capacity().release_capacity(capacity) {
                    self.payload.set_error(PayloadError::Http2(err))
                }
            }
        }
    }
}

struct IoWrapper<T> {
    unread: Option<Bytes>,
    inner: T,
}

impl<T: Read> Read for IoWrapper<T> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        if let Some(mut bytes) = self.unread.take() {
            let size = cmp::min(buf.len(), bytes.len());
            buf[..size].copy_from_slice(&bytes[..size]);
            if bytes.len() > size {
                bytes.split_to(size);
                self.unread = Some(bytes);
            }
            Ok(size)
        } else {
            self.inner.read(buf)
        }
    }
}

impl<T: Write> Write for IoWrapper<T> {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.inner.write(buf)
    }
    fn flush(&mut self) -> io::Result<()> {
        self.inner.flush()
    }
}

impl<T: AsyncRead + 'static> AsyncRead for IoWrapper<T> {
    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool {
        self.inner.prepare_uninitialized_buffer(buf)
    }
}

impl<T: AsyncWrite + 'static> AsyncWrite for IoWrapper<T> {
    fn shutdown(&mut self) -> Poll<(), io::Error> {
        self.inner.shutdown()
    }
    fn write_buf<B: Buf>(&mut self, buf: &mut B) -> Poll<usize, io::Error> {
        self.inner.write_buf(buf)
    }
}