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// Copyright 2019 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.

use crate::PlainText2Config;
use crate::error::PlainTextError;
use crate::structs_proto::Exchange;

use bytes::{Bytes, BytesMut};
use futures::prelude::*;
use asynchronous_codec::{Framed, FramedParts};
use libp2p_core::{PublicKey, PeerId};
use log::{debug, trace};
use prost::Message;
use std::io::{Error as IoError, ErrorKind as IoErrorKind};
use unsigned_varint::codec::UviBytes;

struct HandshakeContext<T> {
    config: PlainText2Config,
    state: T
}

// HandshakeContext<()> --with_local-> HandshakeContext<Local>
struct Local {
    // Our local exchange's raw bytes:
    exchange_bytes: Vec<u8>,
}

// HandshakeContext<Local> --with_remote-> HandshakeContext<Remote>
pub struct Remote {
    // The remote's peer ID:
    pub peer_id: PeerId,
    // The remote's public key:
    pub public_key: PublicKey,
}

impl HandshakeContext<Local> {
    fn new(config: PlainText2Config) -> Result<Self, PlainTextError> {
        let exchange = Exchange {
            id: Some(config.local_public_key.clone().into_peer_id().to_bytes()),
            pubkey: Some(config.local_public_key.clone().into_protobuf_encoding())
        };
        let mut buf = Vec::with_capacity(exchange.encoded_len());
        exchange.encode(&mut buf).expect("Vec<u8> provides capacity as needed");

        Ok(Self {
            config,
            state: Local {
                exchange_bytes: buf
            }
        })
    }

    fn with_remote(self, exchange_bytes: BytesMut)
        -> Result<HandshakeContext<Remote>, PlainTextError>
    {
        let prop = match Exchange::decode(exchange_bytes) {
            Ok(prop) => prop,
            Err(e) => {
                debug!("failed to parse remote's exchange protobuf message");
                return Err(PlainTextError::InvalidPayload(Some(e)));
            },
        };

        let pb_pubkey = prop.pubkey.unwrap_or_default();
        let public_key = match PublicKey::from_protobuf_encoding(pb_pubkey.as_slice()) {
            Ok(p) => p,
            Err(_) => {
                debug!("failed to parse remote's exchange's pubkey protobuf");
                return Err(PlainTextError::InvalidPayload(None));
            },
        };
        let peer_id = match PeerId::from_bytes(&prop.id.unwrap_or_default()) {
            Ok(p) => p,
            Err(_) => {
                debug!("failed to parse remote's exchange's id protobuf");
                return Err(PlainTextError::InvalidPayload(None));
            },
        };

        // Check the validity of the remote's `Exchange`.
        if peer_id != public_key.clone().into_peer_id() {
            debug!("the remote's `PeerId` isn't consistent with the remote's public key");
            return Err(PlainTextError::InvalidPeerId)
        }

        Ok(HandshakeContext {
            config: self.config,
            state: Remote {
                peer_id,
                public_key,
            }
        })
    }
}

pub async fn handshake<S>(socket: S, config: PlainText2Config)
    -> Result<(S, Remote, Bytes), PlainTextError>
where
    S: AsyncRead + AsyncWrite + Send + Unpin,
{
    // The handshake messages all start with a variable-length integer indicating the size.
    let mut framed_socket = Framed::new(socket, UviBytes::default());

    trace!("starting handshake");
    let context = HandshakeContext::new(config)?;

    trace!("sending exchange to remote");
    framed_socket.send(BytesMut::from(&context.state.exchange_bytes[..])).await?;

    trace!("receiving the remote's exchange");
    let context = match framed_socket.next().await {
        Some(p) => context.with_remote(p?)?,
        None => {
            debug!("unexpected eof while waiting for remote's exchange");
            let err = IoError::new(IoErrorKind::BrokenPipe, "unexpected eof");
            return Err(err.into());
        }
    };

    trace!("received exchange from remote; pubkey = {:?}", context.state.public_key);

    let FramedParts { io, read_buffer, write_buffer, .. } = framed_socket.into_parts();
    assert!(write_buffer.is_empty());
    Ok((io, context.state, read_buffer.freeze()))
}