use anyhow::Result;
use bytes::Bytes;
use std::collections::HashMap;

use ostp_core::relay::RelayMessage;
use tokio::io::AsyncReadExt;
use tokio::net::UdpSocket;
use tokio::sync::mpsc;

use crate::dispatcher::Dispatcher;
use crate::outbound::{self, OutboundConfig};
use crate::{RemoteState, UiEvent};

pub async fn handle_relay_message(
    peer_addr: std::net::SocketAddr,
    session_id: u32,
    stream_id: u16,
    payload: Bytes,
    dispatcher: &mut Dispatcher,
    socket: &UdpSocket,
    remotes: &mut HashMap<(u32, u16), RemoteState>,
    ui_event_tx: &mpsc::UnboundedSender<UiEvent>,
    stream_tx: mpsc::UnboundedSender<(u32, u16, Vec<u8>)>,
    udp_reply_tx: mpsc::UnboundedSender<(u32, u16, String, Vec<u8>)>,
    connect_tx: mpsc::UnboundedSender<(u32, u16, String, Result<(tokio::net::tcp::OwnedWriteHalf, mpsc::Sender<()>), String>)>,
    outbound_cfg: Option<OutboundConfig>,
    dns_server: std::sync::Arc<crate::dns::DnsServer>,
    debug: bool,
    tcp_map: &std::sync::Arc<tokio::sync::RwLock<HashMap<std::net::SocketAddr, tokio::sync::mpsc::Sender<Bytes>>>>,
) -> Result<()> {
    match RelayMessage::decode(&payload)? {
        RelayMessage::Connect(target) => {
            // Intercept DNS queries directed at the TUN gateway if our internal DNS is enabled
            let is_internal_dns = {
                target == "10.1.0.1:53" && dns_server.config.read().await.enabled
            };

            if is_internal_dns {
                let client_ip = peer_addr.ip();
                let dns_srv = dns_server.clone();
                let stream_tx_dns = stream_tx.clone();
                let (cancel_tx, _) = mpsc::channel::<()>(1);
                
                let (dns_query_tx, mut dns_query_rx) = mpsc::unbounded_channel::<Bytes>();

                tokio::spawn(async move {
                    if let Some(query_bytes) = dns_query_rx.recv().await {
                        if let Some(resp_bytes) = dns_srv.resolve(&query_bytes, client_ip).await {
                            let _ = stream_tx_dns.send((session_id, stream_id, resp_bytes));
                        }
                    }
                    let _ = stream_tx_dns.send((session_id, stream_id, Vec::new()));
                });

                remotes.insert((session_id, stream_id), RemoteState {
                    data_tx: dns_query_tx,
                    udp_tx: None,
                    cancel_tx,
                    is_dns: true,
                });

                send_relay_to_stream(session_id, stream_id, RelayMessage::ConnectOk, dispatcher, socket, ui_event_tx, tcp_map).await?;
                return Ok(());
            }

            let mut connect_target = target.clone();
            if connect_target.starts_with("10.1.0.1:") {
                connect_target = connect_target.replace("10.1.0.1:", "127.0.0.1:");
            }

            let target_clone = connect_target.clone();
            let connect_tx_clone = connect_tx.clone();
            let stream_tx_clone = stream_tx.clone();
            let outbound_clone = outbound_cfg.clone();
            tokio::spawn(async move {
                let stream_res = outbound::connect_target(&target_clone, outbound_clone.as_ref(), debug).await;
                match stream_res {
                    Ok(stream) => {
                        let (mut reader, writer) = stream.into_split();
                        let (cancel_tx, mut cancel_rx) = mpsc::channel::<()>(1);
                        tokio::spawn(async move {
                            let mut buf = [0_u8; 4096];
                            loop {
                                tokio::select! {
                                    _ = cancel_rx.recv() => break,
                                    read_res = reader.read(&mut buf) => {
                                        match read_res {
                                            Ok(0) | Err(_) => {
                                                let _ = stream_tx_clone.send((session_id, stream_id, Vec::new()));
                                                break;
                                            }
                                            Ok(n) => {
                                                if stream_tx_clone.send((session_id, stream_id, buf[..n].to_vec())).is_err() {
                                                    break;
                                                }
                                            }
                                        }
                                    }
                                }
                            }
                        });
                        let _ = connect_tx_clone.send((session_id, stream_id, target_clone, Ok((writer, cancel_tx))));
                    }
                    Err(e) => {
                        let _ = connect_tx_clone.send((session_id, stream_id, target_clone, Err(e.to_string())));
                    }
                }
            });
        }
        RelayMessage::Data(data) => {
            if let Some(remote) = remotes.get_mut(&(session_id, stream_id)) {
                let _ = remote.data_tx.send(bytes::Bytes::from(data));
            } else {
                let _ = ui_event_tx.send(UiEvent::Log(format!("Relay DATA for unknown stream [{session_id}:{stream_id}] ({})", data.len())));
            }
        }
        RelayMessage::KeepAlive => {}
        RelayMessage::Close => {
            if let Some(state) = remotes.remove(&(session_id, stream_id)) {
                let _ = state.cancel_tx.try_send(());
                let _ = ui_event_tx.send(UiEvent::Log(format!("Relay CLOSE [{session_id}:{stream_id}]")));
            }
        }
        RelayMessage::ConnectOk => {}
        RelayMessage::Error(msg) => {
            let _ = ui_event_tx.send(UiEvent::Log(format!("Relay error from [{session_id}:{stream_id}]: {msg}")));
        }
        RelayMessage::Ping(ts) => {
            send_relay_to_stream(session_id, stream_id, RelayMessage::Pong(ts), dispatcher, socket, ui_event_tx, tcp_map).await?;
        }
        RelayMessage::Pong(_) => {}
        RelayMessage::UdpAssociate => {
            if debug {
                let _ = ui_event_tx.send(UiEvent::Log(format!("Relay UDP ASSOCIATE stream_id={stream_id}")));
            }
            let udp_bind_result = match UdpSocket::bind("[::]:0").await {
                Ok(s) => Ok(s),
                Err(_) => UdpSocket::bind("0.0.0.0:0").await,
            };
            let server_udp = match udp_bind_result {
                Ok(s) => std::sync::Arc::new(s),
                Err(e) => {
                    let _ = ui_event_tx.send(UiEvent::Log(format!("UDP bind failed: {e}")));
                    return Ok(());
                }
            };
            
            let (udp_tx, mut udp_rx) = mpsc::unbounded_channel::<(String, Bytes)>();
            let (cancel_tx, mut cancel_rx) = mpsc::channel::<()>(1);
            let (dummy_data_tx, _) = mpsc::unbounded_channel::<Bytes>();

            // Outbound UDP loop (tunnel -> target)
            let tx_sock = server_udp.clone();
            let dns_srv = dns_server.clone();
            let udp_reply_clone_dns = udp_reply_tx.clone();
            let client_ip = peer_addr.ip();
            tokio::spawn(async move {
                while let Some((target, data)) = udp_rx.recv().await {
                    let is_internal_dns = target == "10.1.0.1:53" && dns_srv.config.read().await.enabled;
                    if is_internal_dns {
                        if let Some(resp_bytes) = dns_srv.resolve(&data, client_ip).await {
                            let _ = udp_reply_clone_dns.send((session_id, stream_id, target, resp_bytes));
                        }
                    } else {
                        let mut forward_target = target.clone();
                        if forward_target.starts_with("10.1.0.1:") {
                            forward_target = forward_target.replace("10.1.0.1:", "127.0.0.1:");
                        }
                        let _ = tx_sock.send_to(&data, &forward_target).await;
                    }
                }
            });

            // Inbound UDP loop (target -> tunnel)
            let rx_sock = server_udp.clone();
            let udp_reply_clone = udp_reply_tx.clone();
            tokio::spawn(async move {
                let mut buf = vec![0u8; 65536];
                loop {
                    tokio::select! {
                        _ = cancel_rx.recv() => break,
                        res = rx_sock.recv_from(&mut buf) => {
                            match res {
                                Ok((len, addr)) => {
                                    let _ = udp_reply_clone.send((session_id, stream_id, addr.to_string(), buf[..len].to_vec()));
                                }
                                Err(_) => break,
                            }
                        }
                    }
                }
            });

            remotes.insert((session_id, stream_id), RemoteState {
                data_tx: dummy_data_tx,
                udp_tx: Some(udp_tx),
                cancel_tx,
                is_dns: false,
            });

            send_relay_to_stream(session_id, stream_id, RelayMessage::ConnectOk, dispatcher, socket, ui_event_tx, tcp_map).await?;
        }
        RelayMessage::UdpData(target, data) => {
            if let Some(remote) = remotes.get_mut(&(session_id, stream_id)) {
                if let Some(ref udp_tx) = remote.udp_tx {
                    let _ = udp_tx.send((target, Bytes::from(data)));
                }
            } else {
                let _ = ui_event_tx.send(UiEvent::Log(format!("Relay UDP DATA for unknown stream [{session_id}:{stream_id}]")));
            }
        }
    }
    Ok(())
}

pub async fn send_relay_to_stream(
    session_id: u32,
    stream_id: u16,
    msg: RelayMessage,
    dispatcher: &mut Dispatcher,
    socket: &UdpSocket,
    ui_event_tx: &mpsc::UnboundedSender<UiEvent>,
    tcp_map: &std::sync::Arc<tokio::sync::RwLock<HashMap<std::net::SocketAddr, tokio::sync::mpsc::Sender<Bytes>>>>,
) -> Result<()> {
    let payload = Bytes::from(msg.encode());
    if let Some((frame, peer_addr)) = dispatcher.outbound_to_session(session_id, stream_id, payload)? {
        let response_len = frame.len();
        let mut sent_tcp = false;
        {
            let map = tcp_map.read().await;
            if let Some(tx) = map.get(&peer_addr) {
                let _ = tx.try_send(frame.clone());
                sent_tcp = true;
            }
        }
        if !sent_tcp {
            let _ = socket.send_to(&frame, peer_addr).await?;
        }
        let _ = ui_event_tx.send(UiEvent::Tx {
            peer: peer_addr.ip(),
            bytes: response_len,
        });
    }
    Ok(())
}