// Copyright 2018 Parity Technologies (UK) Ltd.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

//! Muxing is the process of splitting a connection into multiple substreams.
//!
//! The main item of this module is the `StreamMuxer` trait. An implementation of `StreamMuxer`
//! has ownership of a connection, lets you open and close substreams, and read/write data
//! on open substreams.
//!
//! > **Note**: You normally don't need to use the methods of the `StreamMuxer` directly, as this
//! >           is managed by the library's internals.
//!
//! Each substream of a connection is an isolated stream of data. All the substreams are muxed
//! together so that the data read from or written to each substream doesn't influence the other
//! substreams.
//!
//! In the context of libp2p, each substream can use a different protocol. Contrary to opening a
//! connection, opening a substream is almost free in terms of resources. This means that you
//! shouldn't hesitate to rapidly open and close substreams, and to design protocols that don't
//! require maintaining long-lived channels of communication.
//!
//! > **Example**: The Kademlia protocol opens a new substream for each request it wants to
//! >              perform. Multiple requests can be performed simultaneously by opening multiple
//! >              substreams, without having to worry about associating responses with the
//! >              right request.
//!
//! # Implementing a muxing protocol
//!
//! In order to implement a muxing protocol, create an object that implements the `UpgradeInfo`,
//! `InboundUpgrade` and `OutboundUpgrade` traits. See the `upgrade` module for more information.
//! The `Output` associated type of the `InboundUpgrade` and `OutboundUpgrade` traits should be
//! identical, and should be an object that implements the `StreamMuxer` trait.
//!
//! The upgrade process will take ownership of the connection, which makes it possible for the
//! implementation of `StreamMuxer` to control everything that happens on the wire.

use fnv::FnvHashMap;
use futures::{future, prelude::*, try_ready};
use parking_lot::Mutex;
use std::io::{Error as IoError, ErrorKind as IoErrorKind, Read, Write};
use std::ops::Deref;
use std::fmt;
use std::sync::atomic::{AtomicUsize, Ordering};
use tokio_io::{AsyncRead, AsyncWrite};

/// Ways to shutdown a substream or stream muxer.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Shutdown {
    /// Shutdown inbound direction.
    Inbound,
    /// Shutdown outbound direction.
    Outbound,
    /// Shutdown everything.
    All
}

/// Implemented on objects that can open and manage substreams.
pub trait StreamMuxer {
    /// Type of the object that represents the raw substream where data can be read and written.
    type Substream;

    /// Future that will be resolved when the outgoing substream is open.
    type OutboundSubstream;

    /// Polls for an inbound substream.
    ///
    /// This function behaves the same as a `Stream`.
    ///
    /// If `NotReady` is returned, then the current task will be notified once the muxer
    /// is ready to be polled, similar to the API of `Stream::poll()`.
    /// However, only the latest task that was used to call this method may be notified.
    fn poll_inbound(&self) -> Poll<Option<Self::Substream>, IoError>;

    /// Opens a new outgoing substream, and produces a future that will be resolved when it becomes
    /// available.
    fn open_outbound(&self) -> Self::OutboundSubstream;

    /// Polls the outbound substream.
    ///
    /// If this returns `Ok(Ready(None))`, that means that the outbound channel is closed and that
    /// opening any further outbound substream will likely produce `None` as well. The existing
    /// outbound substream attempts may however still succeed.
    ///
    /// If `NotReady` is returned, then the current task will be notified once the substream
    /// is ready to be polled, similar to the API of `Future::poll()`.
    /// However, for each individual outbound substream, only the latest task that was used to
    /// call this method may be notified.
    ///
    /// May panic or produce an undefined result if an earlier polling of the same substream
    /// returned `Ready` or `Err`.
    fn poll_outbound(&self, s: &mut Self::OutboundSubstream) -> Poll<Option<Self::Substream>, IoError>;

    /// Destroys an outbound substream. Use this after the outbound substream has finished, or if
    /// you want to interrupt it.
    fn destroy_outbound(&self, s: Self::OutboundSubstream);

    /// Reads data from a substream. The behaviour is the same as `tokio_io::AsyncRead::poll_read`.
    ///
    /// If `NotReady` is returned, then the current task will be notified once the substream
    /// is ready to be read. However, for each individual substream, only the latest task that
    /// was used to call this method may be notified.
    fn read_substream(&self, s: &mut Self::Substream, buf: &mut [u8]) -> Poll<usize, IoError>;

    /// Write data to a substream. The behaviour is the same as `tokio_io::AsyncWrite::poll_write`.
    ///
    /// If `NotReady` is returned, then the current task will be notified once the substream
    /// is ready to be read. However, for each individual substream, only the latest task that
    /// was used to call this method may be notified.
    fn write_substream(&self, s: &mut Self::Substream, buf: &[u8]) -> Poll<usize, IoError>;

    /// Flushes a substream. The behaviour is the same as `tokio_io::AsyncWrite::poll_flush`.
    ///
    /// If `NotReady` is returned, then the current task will be notified once the substream
    /// is ready to be read. However, for each individual substream, only the latest task that
    /// was used to call this method may be notified.
    fn flush_substream(&self, s: &mut Self::Substream) -> Poll<(), IoError>;

    /// Attempts to shut down a substream. The behaviour is similar to
    /// `tokio_io::AsyncWrite::shutdown`.
    ///
    /// Shutting down a substream does not imply `flush_substream`. If you want to make sure
    /// that the remote is immediately informed about the shutdown, use `flush_substream` or
    /// `flush`.
    fn shutdown_substream(&self, s: &mut Self::Substream, kind: Shutdown) -> Poll<(), IoError>;

    /// Destroys a substream.
    fn destroy_substream(&self, s: Self::Substream);

    /// Returns `true` if the remote has shown any sign of activity after the muxer has been open.
    ///
    /// For optimisation purposes, the connection handshake of libp2p can be very optimistic and is
    /// allowed to assume that the handshake has succeeded when it didn't in fact succeed. This
    /// method can be called in order to determine whether the remote has accepted our handshake or
    /// has potentially not received it yet.
    fn is_remote_acknowledged(&self) -> bool;

    /// Shutdown this `StreamMuxer`.
    ///
    /// If supported, sends a hint to the remote that we may no longer open any further outbound
    /// or inbound substream. Calling `poll_outbound` or `poll_inbound` afterwards may or may not
    /// produce `None`.
    ///
    /// Shutting down the muxer does not imply `flush_all`. If you want to make sure that the
    /// remote is immediately informed about the shutdown, use `flush_all`.
    fn shutdown(&self, kind: Shutdown) -> Poll<(), IoError>;

    /// Flush this `StreamMuxer`.
    ///
    /// This drains any write buffers of substreams and otherwise and delivers any pending shutdown
    /// notifications due to `shutdown_substream` or `shutdown`. One may thus shutdown groups of
    /// substreams followed by a final `flush_all` instead of having to do `flush_substream` for
    /// each.
    fn flush_all(&self) -> Poll<(), IoError>;
}

/// Polls for an inbound from the muxer but wraps the output in an object that
/// implements `Read`/`Write`/`AsyncRead`/`AsyncWrite`.
#[inline]
pub fn inbound_from_ref_and_wrap<P>(
    muxer: P,
) -> impl Future<Item = Option<SubstreamRef<P>>, Error = IoError>
where
    P: Deref + Clone,
    P::Target: StreamMuxer,
{
    let muxer2 = muxer.clone();
    future::poll_fn(move || muxer.poll_inbound())
        .map(|substream| substream.map(move |s| substream_from_ref(muxer2, s)))
}

/// Same as `outbound_from_ref`, but wraps the output in an object that
/// implements `Read`/`Write`/`AsyncRead`/`AsyncWrite`.
#[inline]
pub fn outbound_from_ref_and_wrap<P>(muxer: P) -> OutboundSubstreamRefWrapFuture<P>
where
    P: Deref + Clone,
    P::Target: StreamMuxer,
{
    let inner = outbound_from_ref(muxer);
    OutboundSubstreamRefWrapFuture { inner }
}

/// Future returned by `outbound_from_ref_and_wrap`.
pub struct OutboundSubstreamRefWrapFuture<P>
where
    P: Deref + Clone,
    P::Target: StreamMuxer,
{
    inner: OutboundSubstreamRefFuture<P>,
}

impl<P> Future for OutboundSubstreamRefWrapFuture<P>
where
    P: Deref + Clone,
    P::Target: StreamMuxer,
{
    type Item = Option<SubstreamRef<P>>;
    type Error = IoError;

    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
        match self.inner.poll() {
            Ok(Async::Ready(Some(substream))) => {
                let out = substream_from_ref(self.inner.muxer.clone(), substream);
                Ok(Async::Ready(Some(out)))
            }
            Ok(Async::Ready(None)) => Ok(Async::Ready(None)),
            Ok(Async::NotReady) => Ok(Async::NotReady),
            Err(err) => Err(err),
        }
    }
}

/// Builds a new future for an outbound substream, where the muxer is a reference.
#[inline]
pub fn outbound_from_ref<P>(muxer: P) -> OutboundSubstreamRefFuture<P>
where
    P: Deref,
    P::Target: StreamMuxer,
{
    let outbound = muxer.open_outbound();
    OutboundSubstreamRefFuture {
        muxer,
        outbound: Some(outbound),
    }
}

/// Future returned by `outbound_from_ref`.
pub struct OutboundSubstreamRefFuture<P>
where
    P: Deref,
    P::Target: StreamMuxer,
{
    muxer: P,
    outbound: Option<<P::Target as StreamMuxer>::OutboundSubstream>,
}

impl<P> Future for OutboundSubstreamRefFuture<P>
where
    P: Deref,
    P::Target: StreamMuxer,
{
    type Item = Option<<P::Target as StreamMuxer>::Substream>;
    type Error = IoError;

    #[inline]
    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
        self.muxer
            .poll_outbound(self.outbound.as_mut().expect("outbound was empty"))
    }
}

impl<P> Drop for OutboundSubstreamRefFuture<P>
where
    P: Deref,
    P::Target: StreamMuxer,
{
    #[inline]
    fn drop(&mut self) {
        self.muxer
            .destroy_outbound(self.outbound.take().expect("outbound was empty"))
    }
}

/// Builds an implementation of `Read`/`Write`/`AsyncRead`/`AsyncWrite` from an `Arc` to the
/// muxer and a substream.
#[inline]
pub fn substream_from_ref<P>(
    muxer: P,
    substream: <P::Target as StreamMuxer>::Substream,
) -> SubstreamRef<P>
where
    P: Deref,
    P::Target: StreamMuxer,
{
    SubstreamRef {
        muxer,
        substream: Some(substream),
    }
}

/// Stream returned by `substream_from_ref`.
pub struct SubstreamRef<P>
where
    P: Deref,
    P::Target: StreamMuxer,
{
    muxer: P,
    substream: Option<<P::Target as StreamMuxer>::Substream>,
}

impl<P> fmt::Debug for SubstreamRef<P>
where
    P: Deref,
    P::Target: StreamMuxer,
    <P::Target as StreamMuxer>::Substream: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        write!(f, "Substream({:?})", self.substream)
    }
}


impl<P> Read for SubstreamRef<P>
where
    P: Deref,
    P::Target: StreamMuxer,
{
    #[inline]
    fn read(&mut self, buf: &mut [u8]) -> Result<usize, IoError> {
        let s = self.substream.as_mut().expect("substream was empty");
        match self.muxer.read_substream(s, buf)? {
            Async::Ready(n) => Ok(n),
            Async::NotReady => Err(IoErrorKind::WouldBlock.into())
        }
    }
}

impl<P> AsyncRead for SubstreamRef<P>
where
    P: Deref,
    P::Target: StreamMuxer,
{
    #[inline]
    fn poll_read(&mut self, buf: &mut [u8]) -> Poll<usize, IoError> {
        let s = self.substream.as_mut().expect("substream was empty");
        self.muxer.read_substream(s, buf)
    }
}

impl<P> Write for SubstreamRef<P>
where
    P: Deref,
    P::Target: StreamMuxer,
{
    #[inline]
    fn write(&mut self, buf: &[u8]) -> Result<usize, IoError> {
        let s = self.substream.as_mut().expect("substream was empty");
        match self.muxer.write_substream(s, buf)? {
            Async::Ready(n) => Ok(n),
            Async::NotReady => Err(IoErrorKind::WouldBlock.into())
        }
    }

    #[inline]
    fn flush(&mut self) -> Result<(), IoError> {
        let s = self.substream.as_mut().expect("substream was empty");
        match self.muxer.flush_substream(s)? {
            Async::Ready(()) => Ok(()),
            Async::NotReady => Err(IoErrorKind::WouldBlock.into())
        }
    }
}

impl<P> AsyncWrite for SubstreamRef<P>
where
    P: Deref,
    P::Target: StreamMuxer,
{
    #[inline]
    fn poll_write(&mut self, buf: &[u8]) -> Poll<usize, IoError> {
        let s = self.substream.as_mut().expect("substream was empty");
        self.muxer.write_substream(s, buf)
    }

    #[inline]
    fn shutdown(&mut self) -> Poll<(), IoError> {
        let s = self.substream.as_mut().expect("substream was empty");
        self.muxer.shutdown_substream(s, Shutdown::All)?;
        Ok(Async::Ready(()))
    }

    #[inline]
    fn poll_flush(&mut self) -> Poll<(), IoError> {
        let s = self.substream.as_mut().expect("substream was empty");
        self.muxer.flush_substream(s)
    }
}

impl<P> Drop for SubstreamRef<P>
where
    P: Deref,
    P::Target: StreamMuxer,
{
    #[inline]
    fn drop(&mut self) {
        self.muxer.destroy_substream(self.substream.take().expect("substream was empty"))
    }
}

/// Abstract `StreamMuxer`.
pub struct StreamMuxerBox {
    inner: Box<dyn StreamMuxer<Substream = usize, OutboundSubstream = usize> + Send + Sync>,
}

impl StreamMuxerBox {
    /// Turns a stream muxer into a `StreamMuxerBox`.
    pub fn new<T>(muxer: T) -> StreamMuxerBox
    where
        T: StreamMuxer + Send + Sync + 'static,
        T::OutboundSubstream: Send,
        T::Substream: Send,
    {
        let wrap = Wrap {
            inner: muxer,
            substreams: Mutex::new(Default::default()),
            next_substream: AtomicUsize::new(0),
            outbound: Mutex::new(Default::default()),
            next_outbound: AtomicUsize::new(0),
        };

        StreamMuxerBox {
            inner: Box::new(wrap),
        }
    }
}

impl StreamMuxer for StreamMuxerBox {
    type Substream = usize; // TODO: use a newtype
    type OutboundSubstream = usize; // TODO: use a newtype

    #[inline]
    fn poll_inbound(&self) -> Poll<Option<Self::Substream>, IoError> {
        self.inner.poll_inbound()
    }

    #[inline]
    fn open_outbound(&self) -> Self::OutboundSubstream {
        self.inner.open_outbound()
    }

    #[inline]
    fn poll_outbound(&self, s: &mut Self::OutboundSubstream) -> Poll<Option<Self::Substream>, IoError> {
        self.inner.poll_outbound(s)
    }

    #[inline]
    fn destroy_outbound(&self, substream: Self::OutboundSubstream) {
        self.inner.destroy_outbound(substream)
    }

    #[inline]
    fn read_substream(&self, s: &mut Self::Substream, buf: &mut [u8]) -> Poll<usize, IoError> {
        self.inner.read_substream(s, buf)
    }

    #[inline]
    fn write_substream(&self, s: &mut Self::Substream, buf: &[u8]) -> Poll<usize, IoError> {
        self.inner.write_substream(s, buf)
    }

    #[inline]
    fn flush_substream(&self, s: &mut Self::Substream) -> Poll<(), IoError> {
        self.inner.flush_substream(s)
    }

    #[inline]
    fn shutdown_substream(&self, s: &mut Self::Substream, kind: Shutdown) -> Poll<(), IoError> {
        self.inner.shutdown_substream(s, kind)
    }

    #[inline]
    fn destroy_substream(&self, s: Self::Substream) {
        self.inner.destroy_substream(s)
    }

    #[inline]
    fn shutdown(&self, kind: Shutdown) -> Poll<(), IoError> {
        self.inner.shutdown(kind)
    }

    #[inline]
    fn is_remote_acknowledged(&self) -> bool {
        self.inner.is_remote_acknowledged()
    }

    #[inline]
    fn flush_all(&self) -> Poll<(), IoError> {
        self.inner.flush_all()
    }
}

struct Wrap<T> where T: StreamMuxer {
    inner: T,
    substreams: Mutex<FnvHashMap<usize, T::Substream>>,
    next_substream: AtomicUsize,
    outbound: Mutex<FnvHashMap<usize, T::OutboundSubstream>>,
    next_outbound: AtomicUsize,
}

impl<T> StreamMuxer for Wrap<T> where T: StreamMuxer {
    type Substream = usize; // TODO: use a newtype
    type OutboundSubstream = usize; // TODO: use a newtype

    #[inline]
    fn poll_inbound(&self) -> Poll<Option<Self::Substream>, IoError> {
        match try_ready!(self.inner.poll_inbound()) {
            Some(substream) => {
                let id = self.next_substream.fetch_add(1, Ordering::Relaxed);
                self.substreams.lock().insert(id, substream);
                Ok(Async::Ready(Some(id)))
            },
            None => Ok(Async::Ready(None)),
        }
    }

    #[inline]
    fn open_outbound(&self) -> Self::OutboundSubstream {
        let outbound = self.inner.open_outbound();
        let id = self.next_outbound.fetch_add(1, Ordering::Relaxed);
        self.outbound.lock().insert(id, outbound);
        id
    }

    #[inline]
    fn poll_outbound(
        &self,
        substream: &mut Self::OutboundSubstream,
    ) -> Poll<Option<Self::Substream>, IoError> {
        let mut list = self.outbound.lock();
        match try_ready!(self.inner.poll_outbound(list.get_mut(substream).unwrap())) {
            Some(substream) => {
                let id = self.next_substream.fetch_add(1, Ordering::Relaxed);
                self.substreams.lock().insert(id, substream);
                Ok(Async::Ready(Some(id)))
            },
            None => Ok(Async::Ready(None)),
        }
    }

    #[inline]
    fn destroy_outbound(&self, substream: Self::OutboundSubstream) {
        let mut list = self.outbound.lock();
        self.inner.destroy_outbound(list.remove(&substream).unwrap())
    }

    #[inline]
    fn read_substream(&self, s: &mut Self::Substream, buf: &mut [u8]) -> Poll<usize, IoError> {
        let mut list = self.substreams.lock();
        self.inner.read_substream(list.get_mut(s).unwrap(), buf)
    }

    #[inline]
    fn write_substream(&self, s: &mut Self::Substream, buf: &[u8]) -> Poll<usize, IoError> {
        let mut list = self.substreams.lock();
        self.inner.write_substream(list.get_mut(s).unwrap(), buf)
    }

    #[inline]
    fn flush_substream(&self, s: &mut Self::Substream) -> Poll<(), IoError> {
        let mut list = self.substreams.lock();
        self.inner.flush_substream(list.get_mut(s).unwrap())
    }

    #[inline]
    fn shutdown_substream(&self, s: &mut Self::Substream, kind: Shutdown) -> Poll<(), IoError> {
        let mut list = self.substreams.lock();
        self.inner.shutdown_substream(list.get_mut(s).unwrap(), kind)
    }

    #[inline]
    fn destroy_substream(&self, substream: Self::Substream) {
        let mut list = self.substreams.lock();
        self.inner.destroy_substream(list.remove(&substream).unwrap())
    }

    #[inline]
    fn shutdown(&self, kind: Shutdown) -> Poll<(), IoError> {
        self.inner.shutdown(kind)
    }

    #[inline]
    fn is_remote_acknowledged(&self) -> bool {
        self.inner.is_remote_acknowledged()
    }

    #[inline]
    fn flush_all(&self) -> Poll<(), IoError> {
        self.inner.flush_all()
    }
}