// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of Parity Ethereum.

// Parity Ethereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Parity Ethereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Parity Ethereum.  If not, see <http://www.gnu.org/licenses/>.

use std::{io, str};
use std::collections::HashMap;
use std::net::SocketAddr;
use std::time::{Duration, Instant};

use ethereum_types::H256;
use log::{debug, trace, warn};
use mio::*;
use mio::deprecated::{EventLoop, Handler};
use mio::tcp::*;
use parity_snappy as snappy;
use rlp::{EMPTY_LIST_RLP, Rlp, RlpStream};

use ethcore_io::{IoContext, StreamToken};
use network::{DisconnectReason, Error, PeerCapabilityInfo, ProtocolId, SessionInfo};
use network::client_version::ClientVersion;
use network::SessionCapabilityInfo;

use crate::{
	connection::{Connection, EncryptedConnection, MAX_PAYLOAD_SIZE, Packet},
	handshake::Handshake,
	host::HostInfo,
	node_table::NodeId,
};

// Timeout must be less than (interval - 1).
const PING_TIMEOUT: Duration = Duration::from_secs(60);
const PING_INTERVAL: Duration = Duration::from_secs(120);
const MIN_PROTOCOL_VERSION: u32 = 4;
const MIN_COMPRESSION_PROTOCOL_VERSION: u32 = 5;

#[derive(Debug, Clone)]
enum ProtocolState {
	// Packets pending protocol on_connect event return.
	Pending(Vec<(Vec<u8>, u8)>),
	// Protocol connected.
	Connected,
}

/// Peer session over encrypted connection.
/// When created waits for Hello packet exchange and signals ready state.
/// Sends and receives protocol packets and handles basic packets such as ping/pong and disconnect.
pub struct Session {
	/// Shared session information
	pub info: SessionInfo,
	/// Session ready flag. Set after successful Hello packet exchange
	had_hello: bool,
	/// Session is no longer active flag.
	expired: bool,
	ping_time: Instant,
	pong_time: Option<Instant>,
	state: State,
	// Protocol states -- accumulates pending packets until signaled as ready.
	protocol_states: HashMap<ProtocolId, ProtocolState>,
	compression: bool,
}

enum State {
	Handshake(Handshake),
	Session(EncryptedConnection),
}

/// Structure used to report various session events.
pub enum SessionData {
	None,
	/// Session is ready to send/receive packets.
	Ready,
	/// A packet has been received
	Packet {
		/// Packet data
		data: Vec<u8>,
		/// Packet protocol ID
		protocol: [u8; 3],
		/// Zero based packet ID
		packet_id: u8,
	},
	/// Session has more data to be read
	Continue,
}

const PACKET_HELLO: u8 = 0x80;
const PACKET_DISCONNECT: u8 = 0x01;
const PACKET_PING: u8 = 0x02;
const PACKET_PONG: u8 = 0x03;
const PACKET_GET_PEERS: u8 = 0x04;
const PACKET_PEERS: u8 = 0x05;
const PACKET_USER: u8 = 0x10;
const PACKET_LAST: u8 = 0x7f;

impl Session {
	/// Create a new session out of completed handshake. This clones the handshake connection object
	/// and leaves the handshake in limbo to be de-registered from the event loop.
	pub fn new<Message>(io: &IoContext<Message>, socket: TcpStream, token: StreamToken, id: Option<&NodeId>,
		nonce: &H256, host: &HostInfo) -> Result<Session, Error>
		where Message: Send + Clone + Sync + 'static {
		let originated = id.is_some();
		let mut handshake = Handshake::new(token, id, socket, nonce);
		let local_addr = handshake.connection.local_addr_str();
		handshake.start(io, host, originated)?;
		Ok(Session {
			state: State::Handshake(handshake),
			had_hello: false,
			info: SessionInfo {
				id: id.cloned(),
				client_version: ClientVersion::from(""),
				protocol_version: 0,
				capabilities: Vec::new(),
				peer_capabilities: Vec::new(),
				ping: None,
				originated,
				remote_address: "Handshake".to_owned(),
				local_address: local_addr,
			},
			ping_time: Instant::now(),
			pong_time: None,
			expired: false,
			protocol_states: HashMap::new(),
			compression: false,
		})
	}

	fn complete_handshake<Message>(&mut self, io: &IoContext<Message>, host: &HostInfo) -> Result<(), Error> where Message: Send + Sync + Clone {
		let connection = if let State::Handshake(ref mut h) = self.state {
			self.info.id = Some(h.id);
			self.info.remote_address = h.connection.remote_addr_str();
			EncryptedConnection::new(h)?
		} else {
			panic!("Unexpected state");
		};
		self.state = State::Session(connection);
		self.write_hello(io, host)?;
		Ok(())
	}

	fn connection(&self) -> &Connection {
		match self.state {
			State::Handshake(ref h) => &h.connection,
			State::Session(ref s) => &s.connection,
		}
	}

	/// Get id of the remote peer
	pub fn id(&self) -> Option<&NodeId> {
		self.info.id.as_ref()
	}

	/// Check if session is ready to send/receive data
	pub fn is_ready(&self) -> bool {
		self.had_hello
	}

	/// Mark this session as inactive to be deleted lated.
	pub fn set_expired(&mut self) {
		self.expired = true;
	}

	/// Check if this session is expired.
	pub fn expired(&self) -> bool {
		self.expired
	}

	/// Check if this session is over and there is nothing to be sent.
	pub fn done(&self) -> bool {
		self.expired() && !self.connection().is_sending()
	}

	/// Get remote peer address
	pub fn remote_addr(&self) -> io::Result<SocketAddr> {
		self.connection().remote_addr()
	}

	/// Readable IO handler. Returns packet data if available.
	pub fn readable<Message>(&mut self, io: &IoContext<Message>, host: &HostInfo) -> Result<SessionData, Error>  where Message: Send + Sync + Clone {
		if self.expired() {
			return Ok(SessionData::None)
		}
		let mut create_session = false;
		let mut packet_data = None;
		match self.state {
			State::Handshake(ref mut h) => {
				h.readable(io, host)?;
				if h.done() {
					create_session = true;
				}
			}
			State::Session(ref mut c) => {
				match c.readable(io)? {
					data @ Some(_) => packet_data = data,
					None => return Ok(SessionData::None)
				}
			}
		}
		if let Some(data) = packet_data {
			return Ok(self.read_packet(io, &data, host)?);
		}
		if create_session {
			self.complete_handshake(io, host)?;
            io.update_registration(self.token()).unwrap_or_else(|e| debug!(target: "network", "Token registration error: {:?}", e));
		}
		Ok(SessionData::None)
	}

	/// Writable IO handler. Sends pending packets.
	pub fn writable<Message>(&mut self, io: &IoContext<Message>, _host: &HostInfo) -> Result<(), Error> where Message: Send + Sync + Clone {
		match self.state {
			State::Handshake(ref mut h) => h.writable(io),
			State::Session(ref mut s) => s.writable(io),
		}
	}

	/// Checks if peer supports given capability
	pub fn have_capability(&self, protocol: [u8; 3]) -> bool {
		self.info.capabilities.iter().any(|c| c.protocol == protocol)
	}

	/// Checks if peer supports given capability
	pub fn capability_version(&self, protocol: [u8; 3]) -> Option<u8> {
		self.info.capabilities.iter().filter_map(|c| if c.protocol == protocol { Some(c.version) } else { None }).max()
	}

	/// Register the session socket with the event loop
	pub fn register_socket<Host:Handler<Timeout = Token>>(&self, reg: Token, event_loop: &mut EventLoop<Host>) -> Result<(), Error> {
		if self.expired() {
			return Ok(());
		}
		self.connection().register_socket(reg, event_loop)?;
		Ok(())
	}

	/// Update registration with the event loop. Should be called at the end of the IO handler.
	pub fn update_socket<Host:Handler>(&self, reg:Token, event_loop: &mut EventLoop<Host>) -> Result<(), Error> {
		self.connection().update_socket(reg, event_loop)?;
		Ok(())
	}

	/// Delete registration
	pub fn deregister_socket<Host:Handler>(&self, event_loop: &mut EventLoop<Host>) -> Result<(), Error> {
		self.connection().deregister_socket(event_loop)?;
		Ok(())
	}

	/// Send a protocol packet to peer.
	pub fn send_packet<Message>(&mut self, io: &IoContext<Message>, protocol: Option<[u8; 3]>, packet_id: u8, data: &[u8]) -> Result<(), Error>
        where Message: Send + Sync + Clone {
		if protocol.is_some() && (self.info.capabilities.is_empty() || !self.had_hello) {
			debug!(target: "network", "Sending to unconfirmed session {}, protocol: {:?}, packet: {}", self.token(), protocol.as_ref().map(|p| str::from_utf8(&p[..]).unwrap_or("??")), packet_id);
			return Err(Error::BadProtocol);
		}
		if self.expired() {
			return Err(Error::Expired);
		}
		let mut i = 0usize;
		let pid = match protocol {
			Some(protocol) => {
				while protocol != self.info.capabilities[i].protocol {
					i += 1;
					if i == self.info.capabilities.len() {
						debug!(target: "network", "Unknown protocol: {:?}", protocol);
						return Ok(())
					}
				}
				self.info.capabilities[i].id_offset + packet_id
			},
			None => packet_id
		};
		let mut rlp = RlpStream::new();
		rlp.append(&(u32::from(pid)));
		let mut compressed = Vec::new();
		let mut payload = data; // create a reference with local lifetime
		if self.compression {
			if payload.len() > MAX_PAYLOAD_SIZE {
				return Err(Error::OversizedPacket);
			}
			let len = snappy::compress_into(&payload, &mut compressed);
			trace!(target: "network", "compressed {} to {}", payload.len(), len);
			payload = &compressed[0..len];
		}
		rlp.append_raw(payload, 1);
		self.send(io, &rlp.drain())
	}

	/// Keep this session alive. Returns false if ping timeout happened
	pub fn keep_alive<Message>(&mut self, io: &IoContext<Message>) -> bool where Message: Send + Sync + Clone {
		if let State::Handshake(_) = self.state {
			return true;
		}
		let timed_out = if let Some(pong) = self.pong_time {
			pong.duration_since(self.ping_time) > PING_TIMEOUT
		} else {
			self.ping_time.elapsed() > PING_TIMEOUT
		};

		if !timed_out && self.ping_time.elapsed() > PING_INTERVAL {
			if let Err(e) = self.send_ping(io) {
				debug!("Error sending ping message: {:?}", e);
			}
		}
		!timed_out
	}

	pub fn token(&self) -> StreamToken {
		self.connection().token()
	}

	/// Signal that a subprotocol has handled the connection successfully and
	/// get all pending packets in order received.
	pub fn mark_connected(&mut self, protocol: ProtocolId) -> Vec<(ProtocolId, u8, Vec<u8>)> {
		match self.protocol_states.insert(protocol, ProtocolState::Connected) {
			None => Vec::new(),
			Some(ProtocolState::Connected) => {
				debug!(target: "network", "Protocol {:?} marked as connected more than once", protocol);
				Vec::new()
			}
			Some(ProtocolState::Pending(pending)) =>
				pending.into_iter().map(|(data, id)| (protocol, id, data)).collect(),
		}
	}

	fn read_packet<Message>(&mut self, io: &IoContext<Message>, packet: &Packet, host: &HostInfo) -> Result<SessionData, Error>
	where Message: Send + Sync + Clone {
		if packet.data.len() < 2 {
			return Err(Error::BadProtocol);
		}
		let packet_id = packet.data[0];
		if packet_id != PACKET_HELLO && packet_id != PACKET_DISCONNECT && !self.had_hello {
			return Err(Error::BadProtocol);
		}
		let data = if self.compression {
			let compressed = &packet.data[1..];
			if snappy::decompressed_len(&compressed)? > MAX_PAYLOAD_SIZE {
				return Err(Error::OversizedPacket);
			}
			snappy::decompress(&compressed)?
		} else {
			packet.data[1..].to_owned()
		};
		match packet_id {
			PACKET_HELLO => {
				let rlp = Rlp::new(&data); //TODO: validate rlp expected size
				self.read_hello(io, &rlp, host)?;
				Ok(SessionData::Ready)
			},
			PACKET_DISCONNECT => {
				let rlp = Rlp::new(&data);
				let reason: u8 = rlp.val_at(0)?;
				if self.had_hello {
					debug!(target:"network", "Disconnected: {}: {:?}", self.token(), DisconnectReason::from_u8(reason));
				}
				Err(Error::Disconnect(DisconnectReason::from_u8(reason)))
			}
			PACKET_PING => {
				self.send_pong(io)?;
				Ok(SessionData::Continue)
			},
			PACKET_PONG => {
				let time = Instant::now();
				self.pong_time = Some(time);
				self.info.ping = Some(time.duration_since(self.ping_time));
				Ok(SessionData::Continue)
			},
			PACKET_GET_PEERS => Ok(SessionData::None), //TODO;
			PACKET_PEERS => Ok(SessionData::None),
			PACKET_USER ..= PACKET_LAST => {
				let mut i = 0usize;
				while packet_id >= self.info.capabilities[i].id_offset + self.info.capabilities[i].packet_count {
					i += 1;
					if i == self.info.capabilities.len() {
						debug!(target: "network", "Unknown packet: {:?}", packet_id);
						return Ok(SessionData::Continue)
					}
				}

				// map to protocol
				let protocol = self.info.capabilities[i].protocol;
				let protocol_packet_id = packet_id - self.info.capabilities[i].id_offset;

				match *self.protocol_states.entry(protocol).or_insert_with(|| ProtocolState::Pending(Vec::new())) {
					ProtocolState::Connected => {
						trace!(target: "network", "Packet {} mapped to {:?}:{}, i={}, capabilities={:?}", packet_id, protocol, protocol_packet_id, i, self.info.capabilities);
						Ok(SessionData::Packet { data, protocol, packet_id: protocol_packet_id } )
					}
					ProtocolState::Pending(ref mut pending) => {
						trace!(target: "network", "Packet {} deferred until protocol connection event completion", packet_id);
						pending.push((data, protocol_packet_id));

						Ok(SessionData::Continue)
					}
				}
			},
			_ => {
				debug!(target: "network", "Unknown packet: {:?}", packet_id);
				Ok(SessionData::Continue)
			}
		}
	}

	fn write_hello<Message>(&mut self, io: &IoContext<Message>, host: &HostInfo) -> Result<(), Error> where Message: Send + Sync + Clone {
		let mut rlp = RlpStream::new();
		rlp.append_raw(&[PACKET_HELLO as u8], 0);
		rlp.begin_list(5)
			.append(&host.protocol_version)
			.append(&host.client_version())
			.append_list(&host.capabilities)
			.append(&host.local_endpoint.address.port())
			.append(host.id());
		self.send(io, &rlp.drain())
	}

	fn read_hello<Message>(&mut self, io: &IoContext<Message>, rlp: &Rlp, host: &HostInfo) -> Result<(), Error>
	where Message: Send + Sync + Clone {
		let protocol = rlp.val_at::<u32>(0)?;
		let client_version_string = rlp.val_at::<String>(1)?;
		let client_version = ClientVersion::from(client_version_string);
		let peer_caps: Vec<PeerCapabilityInfo> = rlp.list_at(2)?;
		let id = rlp.val_at::<NodeId>(4)?;

		// Intersect with host capabilities
		// Leave only highset mutually supported capability version
		let mut caps: Vec<SessionCapabilityInfo> = Vec::new();
		for hc in &host.capabilities {
			if peer_caps.iter().any(|c| c.protocol == hc.protocol && c.version == hc.version) {
				caps.push(SessionCapabilityInfo {
					protocol: hc.protocol,
					version: hc.version,
					id_offset: 0,
					packet_count: hc.packet_count,
				});
			}
		}

		caps.retain(|c| host.capabilities.iter().any(|hc| hc.protocol == c.protocol && hc.version == c.version));
		let mut i = 0;
		while i < caps.len() {
			if caps.iter().any(|c| c.protocol == caps[i].protocol && c.version > caps[i].version) {
				caps.remove(i);
			} else {
				i += 1;
			}
		}

		// Sort capabilities alphabetically.
		caps.sort();

		i = 0;
		let mut offset: u8 = PACKET_USER;
		while i < caps.len() {
			caps[i].id_offset = offset;
			offset += caps[i].packet_count;
			i += 1;
		}
		debug!(target: "network", "Hello: {} v{} {} {:?}", client_version, protocol, id, caps);
		let protocol = ::std::cmp::min(protocol, host.protocol_version);
		self.info.protocol_version = protocol;
		self.info.client_version = client_version;
		self.info.capabilities = caps;
		self.info.peer_capabilities = peer_caps;
		if self.info.capabilities.is_empty() {
			trace!(target: "network", "No common capabilities with peer.");
			return Err(self.disconnect(io, DisconnectReason::UselessPeer));
		}
		if protocol < MIN_PROTOCOL_VERSION {
			trace!(target: "network", "Peer protocol version mismatch: {}", protocol);
			return Err(self.disconnect(io, DisconnectReason::UselessPeer));
		}
		self.compression = protocol >= MIN_COMPRESSION_PROTOCOL_VERSION;
		self.send_ping(io)?;
		self.had_hello = true;
		Ok(())
	}

	/// Send ping packet
	pub fn send_ping<Message>(&mut self, io: &IoContext<Message>) -> Result<(), Error> where Message: Send + Sync + Clone {
		self.send_packet(io, None, PACKET_PING, &EMPTY_LIST_RLP)?;
		self.ping_time = Instant::now();
		self.pong_time = None;
		Ok(())
	}

	fn send_pong<Message>(&mut self, io: &IoContext<Message>) -> Result<(), Error> where Message: Send + Sync + Clone {
		self.send_packet(io, None, PACKET_PONG, &EMPTY_LIST_RLP)
	}

	/// Disconnect this session
	pub fn disconnect<Message>(&mut self, io: &IoContext<Message>, reason: DisconnectReason) -> Error where Message: Send + Sync + Clone {
		if let State::Session(_) = self.state {
			let mut rlp = RlpStream::new();
			rlp.begin_list(1);
			rlp.append(&(reason as u32));
			self.send_packet(io, None, PACKET_DISCONNECT, &rlp.drain()).ok();
		}
		Error::Disconnect(reason)
	}

	fn send<Message>(&mut self, io: &IoContext<Message>, data: &[u8]) -> Result<(), Error> where Message: Send + Sync + Clone {
		match self.state {
			State::Handshake(_) => {
				warn!(target:"network", "Unexpected send request");
			},
			State::Session(ref mut s) => {
				s.send_packet(io, data)?
			},
		}
		Ok(())
	}
}