// Copyright 2017 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.

//! Tetsy-multistream-select protocol messages an I/O operations for
//! constructing protocol negotiation flows.
//!
//! A protocol negotiation flow is constructed by using the
//! `Stream` and `Sink` implementations of `MessageIO` and
//! `MessageReader`.

use crate::Version;
use crate::length_delimited::{LengthDelimited, LengthDelimitedReader};

use bytes::{Bytes, BytesMut, BufMut};
use futures::{prelude::*, io::IoSlice, ready};
use std::{convert::TryFrom, io, fmt, error::Error, pin::Pin, task::{Context, Poll}};
use unsigned_varint as uvi;

/// The maximum number of supported protocols that can be processed.
const MAX_PROTOCOLS: usize = 1000;

/// The encoded form of a tetsy-multistream-select 1.0.0 header message.
const MSG_MULTISTREAM_1_0: &[u8] = b"/multistream/1.0.0\n";
/// The encoded form of a tetsy-multistream-select 'na' message.
const MSG_PROTOCOL_NA: &[u8] = b"na\n";
/// The encoded form of a tetsy-multistream-select 'ls' message.
const MSG_LS: &[u8] = b"ls\n";

/// The tetsy-multistream-select header lines preceeding negotiation.
///
/// Every [`Version`] has a corresponding header line.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum HeaderLine {
    /// The `/multistream/1.0.0` header line.
    V1,
}

impl From<Version> for HeaderLine {
    fn from(v: Version) -> HeaderLine {
        match v {
            Version::V1 | Version::V1Lazy => HeaderLine::V1,
        }
    }
}

/// A protocol (name) exchanged during protocol negotiation.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Protocol(Bytes);

impl AsRef<[u8]> for Protocol {
    fn as_ref(&self) -> &[u8] {
        self.0.as_ref()
    }
}

impl TryFrom<Bytes> for Protocol {
    type Error = ProtocolError;

    fn try_from(value: Bytes) -> Result<Self, Self::Error> {
        if !value.as_ref().starts_with(b"/") {
            return Err(ProtocolError::InvalidProtocol)
        }
        Ok(Protocol(value))
    }
}

impl TryFrom<&[u8]> for Protocol {
    type Error = ProtocolError;

    fn try_from(value: &[u8]) -> Result<Self, Self::Error> {
        Self::try_from(Bytes::copy_from_slice(value))
    }
}

impl fmt::Display for Protocol {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", String::from_utf8_lossy(&self.0))
    }
}

/// A tetsy-multistream-select protocol message.
///
/// Tetsy-multistream-select protocol messages are exchanged with the goal
/// of agreeing on a application-layer protocol to use on an I/O stream.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Message {
    /// A header message identifies the tetsy-multistream-select protocol
    /// that the sender wishes to speak.
    Header(HeaderLine),
    /// A protocol message identifies a protocol request or acknowledgement.
    Protocol(Protocol),
    /// A message through which a peer requests the complete list of
    /// supported protocols from the remote.
    ListProtocols,
    /// A message listing all supported protocols of a peer.
    Protocols(Vec<Protocol>),
    /// A message signaling that a requested protocol is not available.
    NotAvailable,
}

impl Message {
    /// Encodes a `Message` into its byte representation.
    pub fn encode(&self, dest: &mut BytesMut) -> Result<(), ProtocolError> {
        match self {
            Message::Header(HeaderLine::V1) => {
                dest.reserve(MSG_MULTISTREAM_1_0.len());
                dest.put(MSG_MULTISTREAM_1_0);
                Ok(())
            }
            Message::Protocol(p) => {
                let len = p.0.as_ref().len() + 1; // + 1 for \n
                dest.reserve(len);
                dest.put(p.0.as_ref());
                dest.put_u8(b'\n');
                Ok(())
            }
            Message::ListProtocols => {
                dest.reserve(MSG_LS.len());
                dest.put(MSG_LS);
                Ok(())
            }
            Message::Protocols(ps) => {
                let mut buf = uvi::encode::usize_buffer();
                let mut encoded = Vec::with_capacity(ps.len());
                for p in ps {
                    encoded.extend(uvi::encode::usize(p.0.as_ref().len() + 1, &mut buf)); // +1 for '\n'
                    encoded.extend_from_slice(p.0.as_ref());
                    encoded.push(b'\n')
                }
                encoded.push(b'\n');
                dest.reserve(encoded.len());
                dest.put(encoded.as_ref());
                Ok(())
            }
            Message::NotAvailable => {
                dest.reserve(MSG_PROTOCOL_NA.len());
                dest.put(MSG_PROTOCOL_NA);
                Ok(())
            }
        }
    }

    /// Decodes a `Message` from its byte representation.
    pub fn decode(mut msg: Bytes) -> Result<Message, ProtocolError> {
        if msg == MSG_MULTISTREAM_1_0 {
            return Ok(Message::Header(HeaderLine::V1))
        }

        if msg == MSG_PROTOCOL_NA {
            return Ok(Message::NotAvailable);
        }

        if msg == MSG_LS {
            return Ok(Message::ListProtocols)
        }

        // If it starts with a `/`, ends with a line feed without any
        // other line feeds in-between, it must be a protocol name.
        if msg.get(0) == Some(&b'/') && msg.last() == Some(&b'\n') &&
            !msg[.. msg.len() - 1].contains(&b'\n')
        {
            let p = Protocol::try_from(msg.split_to(msg.len() - 1))?;
            return Ok(Message::Protocol(p));
        }

        // At this point, it must be an `ls` response, i.e. one or more
        // length-prefixed, newline-delimited protocol names.
        let mut protocols = Vec::new();
        let mut remaining: &[u8] = &msg;
        loop {
            // A well-formed message must be terminated with a newline.
            if remaining == [b'\n'] {
                break
            } else if protocols.len() == MAX_PROTOCOLS {
                return Err(ProtocolError::TooManyProtocols)
            }

            // Decode the length of the next protocol name and check that
            // it ends with a line feed.
            let (len, tail) = uvi::decode::usize(remaining)?;
            if len == 0 || len > tail.len() || tail[len - 1] != b'\n' {
                return Err(ProtocolError::InvalidMessage)
            }

            // Parse the protocol name.
            let p = Protocol::try_from(Bytes::copy_from_slice(&tail[.. len - 1]))?;
            protocols.push(p);

            // Skip ahead to the next protocol.
            remaining = &tail[len ..];
        }

        Ok(Message::Protocols(protocols))
    }
}

/// A `MessageIO` implements a [`Stream`] and [`Sink`] of [`Message`]s.
#[pin_project::pin_project]
pub struct MessageIO<R> {
    #[pin]
    inner: LengthDelimited<R>,
}

impl<R> MessageIO<R> {
    /// Constructs a new `MessageIO` resource wrapping the given I/O stream.
    pub fn new(inner: R) -> MessageIO<R>
    where
        R: AsyncRead + AsyncWrite
    {
        Self { inner: LengthDelimited::new(inner) }
    }

    /// Converts the [`MessageIO`] into a [`MessageReader`], dropping the
    /// [`Message`]-oriented `Sink` in favour of direct `AsyncWrite` access
    /// to the underlying I/O stream.
    ///
    /// This is typically done if further negotiation messages are expected to be
    /// received but no more messages are written, allowing the writing of
    /// follow-up protocol data to commence.
    pub fn into_reader(self) -> MessageReader<R> {
        MessageReader { inner: self.inner.into_reader() }
    }

    /// Drops the [`MessageIO`] resource, yielding the underlying I/O stream.
    ///
    /// # Panics
    ///
    /// Panics if the read buffer or write buffer is not empty, meaning that an incoming
    /// protocol negotiation frame has been partially read or an outgoing frame
    /// has not yet been flushed. The read buffer is guaranteed to be empty whenever
    /// `MessageIO::poll` returned a message. The write buffer is guaranteed to be empty
    /// when the sink has been flushed.
    pub fn into_inner(self) -> R {
        self.inner.into_inner()
    }
}

impl<R> Sink<Message> for MessageIO<R>
where
    R: AsyncWrite,
{
    type Error = ProtocolError;

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

    fn start_send(self: Pin<&mut Self>, item: Message) -> Result<(), Self::Error> {
        let mut buf = BytesMut::new();
        item.encode(&mut buf)?;
        self.project().inner.start_send(buf.freeze()).map_err(From::from)
    }

    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.project().inner.poll_flush(cx).map_err(From::from)
    }

    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.project().inner.poll_close(cx).map_err(From::from)
    }
}

impl<R> Stream for MessageIO<R>
where
    R: AsyncRead
{
    type Item = Result<Message, ProtocolError>;

    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        match poll_stream(self.project().inner, cx) {
            Poll::Pending => Poll::Pending,
            Poll::Ready(None) => Poll::Ready(None),
            Poll::Ready(Some(Ok(m))) => Poll::Ready(Some(Ok(m))),
            Poll::Ready(Some(Err(err))) => Poll::Ready(Some(Err(err))),
        }
    }
}

/// A `MessageReader` implements a `Stream` of `Message`s on an underlying
/// I/O resource combined with direct `AsyncWrite` access.
#[pin_project::pin_project]
#[derive(Debug)]
pub struct MessageReader<R> {
    #[pin]
    inner: LengthDelimitedReader<R>
}

impl<R> MessageReader<R> {
    /// Drops the `MessageReader` resource, yielding the underlying I/O stream
    /// together with the remaining write buffer containing the protocol
    /// negotiation frame data that has not yet been written to the I/O stream.
    ///
    /// # Panics
    ///
    /// Panics if the read buffer or write buffer is not empty, meaning that either
    /// an incoming protocol negotiation frame has been partially read, or an
    /// outgoing frame has not yet been flushed. The read buffer is guaranteed to
    /// be empty whenever `MessageReader::poll` returned a message. The write
    /// buffer is guaranteed to be empty whenever the sink has been flushed.
    pub fn into_inner(self) -> R {
        self.inner.into_inner()
    }
}

impl<R> Stream for MessageReader<R>
where
    R: AsyncRead
{
    type Item = Result<Message, ProtocolError>;

    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        poll_stream(self.project().inner, cx)
    }
}

impl<TInner> AsyncWrite for MessageReader<TInner>
where
    TInner: AsyncWrite
{
    fn poll_write(self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &[u8]) -> Poll<Result<usize, io::Error>> {
        self.project().inner.poll_write(cx, buf)
    }

    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
        self.project().inner.poll_flush(cx)
    }

    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
        self.project().inner.poll_close(cx)
    }

    fn poll_write_vectored(self: Pin<&mut Self>, cx: &mut Context<'_>, bufs: &[IoSlice<'_>]) -> Poll<Result<usize, io::Error>> {
        self.project().inner.poll_write_vectored(cx, bufs)
    }
}

fn poll_stream<S>(stream: Pin<&mut S>, cx: &mut Context<'_>) -> Poll<Option<Result<Message, ProtocolError>>>
where
    S: Stream<Item = Result<Bytes, io::Error>>,
{
    let msg = if let Some(msg) = ready!(stream.poll_next(cx)?) {
        match Message::decode(msg) {
            Ok(m) => m,
            Err(err) => return Poll::Ready(Some(Err(err))),
        }
    } else {
        return Poll::Ready(None)
    };

    log::trace!("Received message: {:?}", msg);

    Poll::Ready(Some(Ok(msg)))
}

/// A protocol error.
#[derive(Debug)]
pub enum ProtocolError {
    /// I/O error.
    IoError(io::Error),

    /// Received an invalid message from the remote.
    InvalidMessage,

    /// A protocol (name) is invalid.
    InvalidProtocol,

    /// Too many protocols have been returned by the remote.
    TooManyProtocols,
}

impl From<io::Error> for ProtocolError {
    fn from(err: io::Error) -> ProtocolError {
        ProtocolError::IoError(err)
    }
}

impl Into<io::Error> for ProtocolError {
    fn into(self) -> io::Error {
        if let ProtocolError::IoError(e) = self {
            return e
        }
        io::ErrorKind::InvalidData.into()
    }
}

impl From<uvi::decode::Error> for ProtocolError {
    fn from(err: uvi::decode::Error) -> ProtocolError {
        Self::from(io::Error::new(io::ErrorKind::InvalidData, err.to_string()))
    }
}

impl Error for ProtocolError {
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        match *self {
            ProtocolError::IoError(ref err) => Some(err),
            _ => None,
        }
    }
}

impl fmt::Display for ProtocolError {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        match self {
            ProtocolError::IoError(e) =>
                write!(fmt, "I/O error: {}", e),
            ProtocolError::InvalidMessage =>
                write!(fmt, "Received an invalid message."),
            ProtocolError::InvalidProtocol =>
                write!(fmt, "A protocol (name) is invalid."),
            ProtocolError::TooManyProtocols =>
                write!(fmt, "Too many protocols received.")
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use quickcheck::*;
    use rand::Rng;
    use rand::distributions::Alphanumeric;
    use std::iter;

    impl Arbitrary for Protocol {
        fn arbitrary<G: Gen>(g: &mut G) -> Protocol {
            let n = g.gen_range(1, g.size());
            let p: String = iter::repeat(())
                .map(|()| g.sample(Alphanumeric))
                .take(n)
                .collect();
            Protocol(Bytes::from(format!("/{}", p)))
        }
    }

    impl Arbitrary for Message {
        fn arbitrary<G: Gen>(g: &mut G) -> Message {
            match g.gen_range(0, 5) {
                0 => Message::Header(HeaderLine::V1),
                1 => Message::NotAvailable,
                2 => Message::ListProtocols,
                3 => Message::Protocol(Protocol::arbitrary(g)),
                4 => Message::Protocols(Vec::arbitrary(g)),
                _ => panic!()
            }
        }
    }

    #[test]
    fn encode_decode_message() {
        fn prop(msg: Message) {
            let mut buf = BytesMut::new();
            msg.encode(&mut buf).expect(&format!("Encoding message failed: {:?}", msg));
            match Message::decode(buf.freeze()) {
                Ok(m) => assert_eq!(m, msg),
                Err(e) => panic!("Decoding failed: {:?}", e)
            }
        }
        quickcheck(prop as fn(_))
    }
}