extern crate slab;

use std::{

    io, io::{Error, ErrorKind, Write},

    net::{SocketAddr, IpAddr, Ipv4Addr},

    collections::HashSet,

    mem::{swap, replace}

};

use mio::{

    net::{TcpStream, TcpListener},

    Poll, PollOpt, Ready, Token

};

use netbuf;

use slab::Slab;

use crate::{

    utils,

    protocol::{ProtocolDecoder, messages::*}

};

use super::{

    server::{HWServer},

    coretypes::ClientId

};

const MAX_BYTES_PER_READ: usize = 2048;

#[derive(Hash, Eq, PartialEq, Copy, Clone)]

pub enum NetworkClientState {

    Idle,

    NeedsWrite,

    NeedsRead,

    Closed,

}

type NetworkResult<T> = io::Result<(T, NetworkClientState)>;

pub struct NetworkClient {

    id: ClientId,

    socket: TcpStream,

    peer_addr: SocketAddr,

    decoder: ProtocolDecoder,

    buf_out: netbuf::Buf

}

impl NetworkClient {

    pub fn new(id: ClientId, socket: TcpStream, peer_addr: SocketAddr) -> NetworkClient {

        NetworkClient {

            id, socket, peer_addr,

            decoder: ProtocolDecoder::new(),

            buf_out: netbuf::Buf::new()

        }

    }

    pub fn read_messages(&mut self) -> NetworkResult<Vec<HWProtocolMessage>> {

        let mut bytes_read = 0;

        let result = loop {

            match self.decoder.read_from(&mut self.socket) {

                Ok(bytes) => {

                    debug!("Client {}: read {} bytes", self.id, bytes);

                    bytes_read += bytes;

                    if bytes == 0 {

                        let result = if bytes_read == 0 {

                            info!("EOF for client {} ({})", self.id, self.peer_addr);

                            (Vec::new(), NetworkClientState::Closed)

                        } else {

                            (self.decoder.extract_messages(), NetworkClientState::NeedsRead)

                        };

                        break Ok(result);

                    }

                    else if bytes_read >= MAX_BYTES_PER_READ {

                        break Ok((self.decoder.extract_messages(), NetworkClientState::NeedsRead))

                    }

                }

                Err(ref error) if error.kind() == ErrorKind::WouldBlock => {

                    let messages =  if bytes_read == 0 {

                        Vec::new()

                    } else {

                        self.decoder.extract_messages()

                    };

                    break Ok((messages, NetworkClientState::Idle));

                }

                Err(error) =>

                    break Err(error)

            }

        };

        self.decoder.sweep();

        result

    }

    pub fn flush(&mut self) -> NetworkResult<()> {

        let result = loop {

            match self.buf_out.write_to(&mut self.socket) {

                Ok(bytes) if self.buf_out.is_empty() || bytes == 0 =>

                    break Ok(((), NetworkClientState::Idle)),

                Ok(_) => (),

                Err(ref error) if error.kind() == ErrorKind::Interrupted

                    || error.kind() == ErrorKind::WouldBlock => {

                    break Ok(((), NetworkClientState::NeedsWrite));

                },

                Err(error) =>

                    break Err(error)

            }

        };

        self.socket.flush()?;

        result

    }

    pub fn send_raw_msg(&mut self, msg: &[u8]) {

        self.buf_out.write_all(msg).unwrap();

    }

    pub fn send_string(&mut self, msg: &str) {

        self.send_raw_msg(&msg.as_bytes());

    }

    pub fn send_msg(&mut self, msg: &HWServerMessage) {

        self.send_string(&msg.to_raw_protocol());

    }

}

pub struct NetworkLayer {

    listener: TcpListener,

    server: HWServer,

    clients: Slab<NetworkClient>,

    pending: HashSet<(ClientId, NetworkClientState)>,

    pending_cache: Vec<(ClientId, NetworkClientState)>

}

impl NetworkLayer {

    pub fn new(listener: TcpListener, clients_limit: usize, rooms_limit: usize) -> NetworkLayer {

        let server = HWServer::new(clients_limit, rooms_limit);

        let clients = Slab::with_capacity(clients_limit);

        let pending = HashSet::with_capacity(2 * clients_limit);

        let pending_cache = Vec::with_capacity(2 * clients_limit);

        NetworkLayer {listener, server, clients, pending, pending_cache}

    }

    pub fn register_server(&self, poll: &Poll) -> io::Result<()> {

        poll.register(&self.listener, utils::SERVER, Ready::readable(),

                      PollOpt::edge())

    }

    fn deregister_client(&mut self, poll: &Poll, id: ClientId) {

        let mut client_exists = false;

        if let Some(ref client) = self.clients.get(id) {

            poll.deregister(&client.socket)

                .expect("could not deregister socket");

            info!("client {} ({}) removed", client.id, client.peer_addr);

            client_exists = true;

        }

        if client_exists {

            self.clients.remove(id);

        }

    }

    fn register_client(&mut self, poll: &Poll, id: ClientId, client_socket: TcpStream, addr: SocketAddr) {

        poll.register(&client_socket, Token(id),

                      Ready::readable() | Ready::writable(),

                      PollOpt::edge())

            .expect("could not register socket with event loop");

        let entry = self.clients.vacant_entry();

        let client = NetworkClient::new(id, client_socket, addr);

        info!("client {} ({}) added", client.id, client.peer_addr);

        entry.insert(client);

    }

    fn flush_server_messages(&mut self) {

        debug!("{} pending server messages", self.server.output.len());

        for (clients, message) in self.server.output.drain(..) {

            debug!("Message {:?} to {:?}", message, clients);

            let msg_string = message.to_raw_protocol();

            for client_id in clients {

                if let Some(client) = self.clients.get_mut(client_id) {

                    client.send_string(&msg_string);

                    self.pending.insert((client_id, NetworkClientState::NeedsWrite));

                }

            }

        }

    }

    pub fn accept_client(&mut self, poll: &Poll) -> io::Result<()> {

        let (client_socket, addr) = self.listener.accept()?;

        info!("Connected: {}", addr);

        let client_id = self.server.add_client();

        self.register_client(poll, client_id, client_socket, addr);

        self.flush_server_messages();

        Ok(())

    }

    fn operation_failed(&mut self, poll: &Poll, client_id: ClientId, error: &Error, msg: &str) -> io::Result<()> {

        let addr = if let Some(ref mut client) = self.clients.get_mut(client_id) {

            client.peer_addr

        } else {

            SocketAddr::new(IpAddr::V4(Ipv4Addr::new(0, 0, 0, 0)), 0)

        };

        debug!("{}({}): {}", msg, addr, error);

        self.client_error(poll, client_id)

    }

    pub fn client_readable(&mut self, poll: &Poll,

                           client_id: ClientId) -> io::Result<()> {

        let messages =

            if let Some(ref mut client) = self.clients.get_mut(client_id) {

                client.read_messages()

            } else {

                warn!("invalid readable client: {}", client_id);

                Ok((Vec::new(), NetworkClientState::Idle))

            };

        match messages {

            Ok((messages, state)) => {

                for message in messages {

                    self.server.handle_msg(client_id, message);

                }

                match state {

                    NetworkClientState::NeedsRead => {

                        self.pending.insert((client_id, state));

                    },

                    NetworkClientState::Closed =>

                        self.client_error(&poll, client_id)?,

                    _ => {}

                };

            }

            Err(e) => self.operation_failed(

                poll, client_id, &e,

                "Error while reading from client socket")?

        }

        self.flush_server_messages();

        if !self.server.removed_clients.is_empty() {

            let ids: Vec<_> = self.server.removed_clients.drain(..).collect();

            for client_id in ids {

                self.deregister_client(poll, client_id);

            }

        }

        Ok(())

    }

    pub fn client_writable(&mut self, poll: &Poll,

                           client_id: ClientId) -> io::Result<()> {

        let result =

            if let Some(ref mut client) = self.clients.get_mut(client_id) {

                client.flush()

            } else {

                warn!("invalid writable client: {}", client_id);

                Ok(((), NetworkClientState::Idle))

            };

        match result {

            Ok(((), state)) if state == NetworkClientState::NeedsWrite => {

                self.pending.insert((client_id, state));

            },

            Ok(_) => {}

            Err(e) => self.operation_failed(

                poll, client_id, &e,

                "Error while writing to client socket")?

        }

        Ok(())

    }

    pub fn client_error(&mut self, poll: &Poll,

                        client_id: ClientId) -> io::Result<()> {

        self.deregister_client(poll, client_id);

        self.server.client_lost(client_id);

        Ok(())

    }

    pub fn has_pending_operations(&self) -> bool {

        !self.pending.is_empty()

    }

    pub fn on_idle(&mut self, poll: &Poll) -> io::Result<()> {

        if self.has_pending_operations() {

            let mut cache = replace(&mut self.pending_cache, Vec::new());

            cache.extend(self.pending.drain());

            for (id, state) in cache.drain(..) {

                match state {

                    NetworkClientState::NeedsRead =>

                        self.client_readable(poll, id)?,

                    NetworkClientState::NeedsWrite =>

                        self.client_writable(poll, id)?,

                    _ => {}

                }

            }

            swap(&mut cache, &mut self.pending_cache);

        }

        Ok(())

    }

}