// Copyright 2016 The Grin Developers
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use std::collections::VecDeque;
use std::sync::RwLock;

use rand::Rng;
use rand::os::OsRng;

use core::ser::{serialize, deserialize, Error};
use msg::*;
use types::*;
use protocol::ProtocolV1;
use peer::PeerConn;

const NONCES_CAP: usize = 100;

/// Handles the handshake negotiation when two peers connect and decides on
/// protocol.
pub struct Handshake {
	/// Ring buffer of nonces sent to detect self connections without requiring
	/// a node id.
	nonces: RwLock<VecDeque<u64>>,
}

unsafe impl Sync for Handshake{}
unsafe impl Send for Handshake{}

impl Handshake {
	/// Creates a new handshake handler
	pub fn new() -> Handshake {
		Handshake { nonces: RwLock::new(VecDeque::with_capacity(NONCES_CAP)) }
	}

	/// Handles connecting to a new remote peer, starting the version handshake.
	pub fn connect<'a>(&'a self, peer: &'a mut PeerConn) -> Result<&Protocol, Error> {
		let nonce = self.next_nonce();

    let sender_addr = SockAddr(peer.local_addr());
    let receiver_addr = SockAddr(peer.peer_addr());
		let opt_err = serialize(peer,
		               &Hand {
			               version: PROTOCOL_VERSION,
			               capabilities: FULL_SYNC,
			               nonce: nonce,
			               sender_addr: sender_addr,
			               receiver_addr: receiver_addr,
			               user_agent: USER_AGENT.to_string(),
		               });
    match opt_err {
      Some(err) => return Err(err),
      None => {}
    }

		let shake = try!(deserialize::<Shake>(peer));
		if shake.version != 1 {
			self.close(peer, ErrCodes::UNSUPPORTED_VERSION as u32,
			           format!("Unsupported version: {}, ours: {})",
			                   shake.version,
			                   PROTOCOL_VERSION));
			return Err(Error::UnexpectedData{expected: vec![PROTOCOL_VERSION as u8], received: vec![shake.version as u8]});
		}
		peer.capabilities = shake.capabilities;
		peer.user_agent = shake.user_agent;
    
		// when more than one protocol version is supported, choosing should go here
		Ok(&ProtocolV1::new(peer))
	}

	/// Handles receiving a connection from a new remote peer that started the
	/// version handshake.
	pub fn handshake<'a>(&'a self, peer: &'a mut PeerConn) -> Result<&Protocol, Error> {
		let hand = try!(deserialize::<Hand>(peer));
		if hand.version != 1 {
			self.close(peer, ErrCodes::UNSUPPORTED_VERSION as u32,
			           format!("Unsupported version: {}, ours: {})",
			                   hand.version,
			                   PROTOCOL_VERSION));
			return Err(Error::UnexpectedData{expected: vec![PROTOCOL_VERSION as u8], received: vec![hand.version as u8]});
		}
    {
      let nonces = self.nonces.read().unwrap();
      if nonces.contains(&hand.nonce) {
        return Err(Error::UnexpectedData {
          expected: vec![],
          received: vec![],
        });
      }
    }

		peer.capabilities = hand.capabilities;
		peer.user_agent = hand.user_agent;

		let opt_err = serialize(peer,
		               &Shake {
			               version: PROTOCOL_VERSION,
			               capabilities: FULL_SYNC,
			               user_agent: USER_AGENT.to_string(),
		               });
    match opt_err {
      Some(err) => return Err(err),
      None => {}
    }

		// when more than one protocol version is supported, choosing should go here
		Ok(&ProtocolV1::new(peer))
	}

	fn next_nonce(&self) -> u64 {
		let mut rng = OsRng::new().unwrap();
		let nonce = rng.next_u64();

		let mut nonces = self.nonces.write().unwrap();
		nonces.push_back(nonce);
		if nonces.len() >= NONCES_CAP {
			nonces.pop_front();
		}
		nonce
	}

	fn close(&self, peer: &mut PeerConn, err_code: u32, explanation: String) {
		serialize(peer,
		          &PeerError {
			          code: err_code,
			          message: explanation,
		          });
		peer.close();
	}
}