use bytes::{Buf, Bytes};

use log::*;

use slab::Slab;

use std::io::Error;

use std::pin::Pin;

use std::task::{Context, Poll};

use std::{

    iter::Iterator,

    net::{IpAddr, SocketAddr},

    time::Duration,

};

use tokio::{

    io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt, ReadBuf},

    net::{TcpListener, TcpStream},

    sync::mpsc::{channel, Receiver, Sender},

};

#[cfg(feature = "tls-connections")]

use tokio_native_tls::{TlsAcceptor, TlsStream};

use crate::{

    core::types::ClientId,

    handlers,

    handlers::{IoResult, IoTask, ServerState},

    protocol::{self, ProtocolDecoder, ProtocolError},

    utils,

};

use hedgewars_network_protocol::{

    messages::HwServerMessage::Redirect, messages::*, parser::server_message,

};

const PING_TIMEOUT: Duration = Duration::from_secs(15);

#[derive(Debug)]

enum ClientUpdateData {

    Message(HwProtocolMessage),

    Error(String),

}

#[derive(Debug)]

struct ClientUpdate {

    client_id: ClientId,

    data: ClientUpdateData,

}

struct ClientUpdateSender {

    client_id: ClientId,

    sender: Sender<ClientUpdate>,

}

impl ClientUpdateSender {

    async fn send(&mut self, data: ClientUpdateData) -> bool {

        self.sender

            .send(ClientUpdate {

                client_id: self.client_id,

                data,

            })

            .await

            .is_ok()

    }

}

enum ClientStream {

    Tcp(TcpStream),

    #[cfg(feature = "tls-connections")]

    Tls(TlsStream<TcpStream>),

}

impl Unpin for ClientStream {}

impl AsyncRead for ClientStream {

    fn poll_read(

        self: Pin<&mut Self>,

        cx: &mut Context<'_>,

        buf: &mut ReadBuf<'_>,

    ) -> Poll<std::io::Result<()>> {

        use ClientStream::*;

        match Pin::into_inner(self) {

            Tcp(stream) => Pin::new(stream).poll_read(cx, buf),

            #[cfg(feature = "tls-connections")]

            Tls(stream) => Pin::new(stream).poll_read(cx, buf),

        }

    }

}

impl AsyncWrite for ClientStream {

    fn poll_write(

        self: Pin<&mut Self>,

        cx: &mut Context<'_>,

        buf: &[u8],

    ) -> Poll<Result<usize, Error>> {

        use ClientStream::*;

        match Pin::into_inner(self) {

            Tcp(stream) => Pin::new(stream).poll_write(cx, buf),

            #[cfg(feature = "tls-connections")]

            Tls(stream) => Pin::new(stream).poll_write(cx, buf),

        }

    }

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

        use ClientStream::*;

        match Pin::into_inner(self) {

            Tcp(stream) => Pin::new(stream).poll_flush(cx),

            #[cfg(feature = "tls-connections")]

            Tls(stream) => Pin::new(stream).poll_flush(cx),

        }

    }

    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Error>> {

        use ClientStream::*;

        match Pin::into_inner(self) {

            Tcp(stream) => Pin::new(stream).poll_shutdown(cx),

            #[cfg(feature = "tls-connections")]

            Tls(stream) => Pin::new(stream).poll_shutdown(cx),

        }

    }

}

struct NetworkClient {

    id: ClientId,

    stream: ClientStream,

    receiver: Receiver<Bytes>,

    peer_addr: SocketAddr,

    decoder: ProtocolDecoder,

}

impl NetworkClient {

    fn new(

        id: ClientId,

        stream: ClientStream,

        peer_addr: SocketAddr,

        receiver: Receiver<Bytes>,

    ) -> Self {

        Self {

            id,

            stream,

            peer_addr,

            receiver,

            decoder: ProtocolDecoder::new(PING_TIMEOUT),

        }

    }

    async fn read<T: AsyncRead + AsyncWrite + Unpin>(

        stream: &mut T,

        decoder: &mut ProtocolDecoder,

    ) -> protocol::Result<HwProtocolMessage> {

        let result = decoder.read_from(stream).await;

        if matches!(result, Err(ProtocolError::Timeout)) {

            if Self::write(stream, Bytes::from(HwServerMessage::Ping.to_raw_protocol())).await {

                decoder.read_from(stream).await

            } else {

                Err(ProtocolError::Eof)

            }

        } else {

            result

        }

    }

    async fn write<T: AsyncWrite + Unpin>(stream: &mut T, mut data: Bytes) -> bool {

        !data.has_remaining() || matches!(stream.write_buf(&mut data).await, Ok(n) if n > 0)

    }

    async fn run(mut self, sender: Sender<ClientUpdate>) {

        use ClientUpdateData::*;

        let mut sender = ClientUpdateSender {

            client_id: self.id,

            sender,

        };

        loop {

            tokio::select! {

                server_message = self.receiver.recv() => {

                    match server_message {

                        Some(message) => if !Self::write(&mut self.stream, message).await {

                            sender.send(Error("Connection reset by peer".to_string())).await;

                            break;

                        }

                        None => {

                            break;

                        }

                    }

                }

                client_message = Self::read(&mut self.stream, &mut self.decoder) => {

                     match client_message {

                        Ok(message) => {

                            //todo!("add flood stats");

                            if !sender.send(Message(message)).await {

                                break;

                            }

                        }

                        Err(e) => {

                            //todo!("send cmdline errors");

                            //todo!("more graceful shutdown to prevent errors from explicitly closed clients")

                            sender.send(Error(format!("{}", e))).await;

                            if matches!(e, ProtocolError::Timeout) {

                                Self::write(&mut self.stream, Bytes::from(HwServerMessage::Bye("Ping timeout".to_string()).to_raw_protocol())).await;

                            }

                            break;

                        }

                    }

                }

            }

        }

    }

}

#[cfg(feature = "tls-connections")]

struct TlsListener {

    listener: TcpListener,

    acceptor: TlsAcceptor,

}

pub struct NetworkLayer {

    listener: TcpListener,

    #[cfg(feature = "tls-connections")]

    tls: TlsListener,

    server_state: ServerState,

    clients: Slab<Sender<Bytes>>,

    update_tx: Sender<ClientUpdate>,

}

impl NetworkLayer {

    pub async fn run(&mut self) {

        async fn accept_plain_branch(

            layer: &mut NetworkLayer,

            value: (TcpStream, SocketAddr),

            update_tx: Sender<ClientUpdate>,

        ) {

            let (stream, addr) = value;

            if let Some(client) = layer.create_client(ClientStream::Tcp(stream), addr).await {

                tokio::spawn(client.run(update_tx));

            }

        }

        #[cfg(feature = "tls-connections")]

        async fn accept_tls_branch(

            layer: &mut NetworkLayer,

            value: (TcpStream, SocketAddr),

            update_tx: Sender<ClientUpdate>,

        ) {

            let (stream, addr) = value;

            match layer.tls.acceptor.accept(stream).await {

                Ok(stream) => {

                    if let Some(client) = layer.create_client(ClientStream::Tls(stream), addr).await

                    {

                        tokio::spawn(client.run(update_tx));

                    }

                }

                Err(e) => {

                    warn!("Unable to establish TLS connection: {}", e);

                }

            }

        }

        async fn client_message_branch(

            layer: &mut NetworkLayer,

            client_message: Option<ClientUpdate>,

        ) {

            use ClientUpdateData::*;

            match client_message {

                Some(ClientUpdate {

                    client_id,

                    data: Message(message),

                }) => {

                    layer.handle_message(client_id, message).await;

                }

                Some(ClientUpdate {

                    client_id,

                    data: Error(e),

                }) => {

                    let mut response = handlers::Response::new(client_id);

                    info!("Client {} error: {:?}", client_id, e);

                    response.remove_client(client_id);

                    handlers::handle_client_loss(&mut layer.server_state, client_id, &mut response);

                    layer.handle_response(response).await;

                }

                None => unreachable!(),

            }

        }

        //todo!("add the DB task");

        //todo!("add certfile watcher task");

        loop {

            #[cfg(not(feature = "tls-connections"))]

            tokio::select! {

                Ok(value) = self.listener.accept() => accept_plain_branch(self, value, self.update_tx.clone()).await,

                client_message = self.update_rx.recv(), if !self.clients.is_empty() => client_message_branch(self, client_message).await

            }

            #[cfg(feature = "tls-connections")]

            tokio::select! {

                Ok(value) = self.listener.accept() => accept_plain_branch(self, value, self.update_tx.clone()).await,

                Ok(value) = self.tls.listener.accept() => accept_tls_branch(self, value, self.update_tx.clone()).await,

                client_message = self.update_rx.recv(), if !self.clients.is_empty() => client_message_branch(self, client_message).await

            }

        }

    }

    async fn create_client(

        &mut self,

        stream: ClientStream,

        addr: SocketAddr,

    ) -> Option<NetworkClient> {

        let entry = self.clients.vacant_entry();

        let client_id = entry.key();

        let (tx, rx) = channel(16);

        entry.insert(tx);

        let client = NetworkClient::new(client_id, stream, addr, rx);

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

        let mut response = handlers::Response::new(client_id);

        let added = if let IpAddr::V4(addr) = client.peer_addr.ip() {

            handlers::handle_client_accept(

                &mut self.server_state,

                client_id,

                &mut response,

                addr.octets(),

                addr.is_loopback(),

            )

        } else {

            todo!("implement something")

        };

        self.handle_response(response).await;

        if added {

            Some(client)

        } else {

            None

        }

    }

    async fn handle_message(&mut self, client_id: ClientId, message: HwProtocolMessage) {

        debug!("Handling message {:?} for client {}", message, client_id);

        let mut response = handlers::Response::new(client_id);

        handlers::handle(&mut self.server_state, client_id, &mut response, message);

        self.handle_response(response).await;

    }

    async fn handle_response(&mut self, mut response: handlers::Response) {

        if response.is_empty() {

            return;

        }

        for client_id in response.extract_removed_clients() {

            if self.clients.contains(client_id) {

                self.clients.remove(client_id);

                if self.clients.is_empty() {

                    let (update_tx, update_rx) = channel(128);

                    self.update_rx = update_rx;

                    self.update_tx = update_tx;

                }

            }

            info!("Client {} removed", client_id);

        }

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

        let output = response.extract_messages(&mut self.server_state.server);

        for (clients, message) in output {

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

            Self::send_message(&mut self.clients, message, clients.iter().cloned()).await;

        }

    }

    async fn send_message<I>(

        clients: &mut Slab<Sender<Bytes>>,

        message: HwServerMessage,

        to_clients: I,

    ) where

        I: Iterator<Item = ClientId>,

    {

        let msg_string = message.to_raw_protocol();

        let bytes = Bytes::copy_from_slice(msg_string.as_bytes());

        for client_id in to_clients {

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

                if !client.send(bytes.clone()).await.is_ok() {

                    clients.remove(client_id);

                }

            }

        }

    }

}

pub struct NetworkLayerBuilder {

    listener: Option<TcpListener>,

    #[cfg(feature = "tls-connections")]

    tls_listener: Option<TcpListener>,

    #[cfg(feature = "tls-connections")]

    tls_acceptor: Option<TlsAcceptor>,

    clients_capacity: usize,

    rooms_capacity: usize,

}

impl Default for NetworkLayerBuilder {

    fn default() -> Self {

        Self {

            clients_capacity: 1024,

            rooms_capacity: 512,

            listener: None,

            #[cfg(feature = "tls-connections")]

            tls_listener: None,

            #[cfg(feature = "tls-connections")]

            tls_acceptor: None,

        }

    }

}

impl NetworkLayerBuilder {

    pub fn with_listener(self, listener: TcpListener) -> Self {

        Self {

            listener: Some(listener),

            ..self

        }

    }

    #[cfg(feature = "tls-connections")]

    pub fn with_tls_acceptor(self, listener: TlsAcceptor) -> Self {

        Self {

            tls_acceptor: Option::from(listener),

            ..self

        }

    }

    #[cfg(feature = "tls-connections")]

    pub fn with_tls_listener(self, listener: TlsAcceptor) -> Self {

        Self {

            tls_acceptor: Option::from(listener),

            ..self

        }

    }

    pub fn build(self) -> NetworkLayer {

        let server_state = ServerState::new(self.clients_capacity, self.rooms_capacity);

        let clients = Slab::with_capacity(self.clients_capacity);

        let (update_tx, update_rx) = channel(128);

        NetworkLayer {

            listener: self.listener.expect("No listener provided"),

            #[cfg(feature = "tls-connections")]

            tls: TlsListener {

                listener: self.tls_listener.expect("No TLS listener provided"),

                acceptor: self.tls_acceptor.expect("No TLS acceptor provided"),

            },

            server_state,

            clients,

            update_tx,

        }

    }

}