use std::collections::HashMap;
use std::net::SocketAddr;

use anyhow::{anyhow, Result};
use chrono::SecondsFormat;
use futures_util::future::join_all;
use nonempty::nonempty;
use nonempty::NonEmpty;
use prometheus::{IntCounter, IntGauge, Registry as MetricsRegistry};
use serde::Deserialize;
use tokio::io::AsyncReadExt;
use tokio::io::{AsyncBufReadExt, AsyncWrite, AsyncWriteExt, BufReader, BufWriter};
use tokio::net::tcp::{ReadHalf, WriteHalf};
use tokio::net::{TcpListener, TcpStream};
use tokio::sync::mpsc::channel;

use lavina_core::auth::Verdict;
use lavina_core::player::*;
use lavina_core::prelude::*;
use lavina_core::room::{RoomId, RoomInfo};
use lavina_core::terminator::Terminator;
use lavina_core::LavinaCore;
use proto_irc::client::CapabilitySubcommand;
use proto_irc::client::{client_message, ClientMessage};
use proto_irc::server::CapSubBody;
use proto_irc::server::{AwayStatus, ServerMessage, ServerMessageBody};
use proto_irc::user::PrefixedNick;
use proto_irc::{Chan, Recipient, Tag};
use sasl::AuthBody;
mod cap;
use handler::Handler;
mod whois;

use crate::cap::Capabilities;

mod handler;

pub const APP_VERSION: &str = concat!("lavina", "_", env!("CARGO_PKG_VERSION"));

#[derive(Deserialize, Debug, Clone)]
pub struct ServerConfig {
    pub listen_on: SocketAddr,
    pub server_name: Str,
}

#[derive(Debug)]
struct RegisteredUser {
    nickname: Str,
    /**
     * Username is mostly unused in modern IRC.
     *
     * <https://stackoverflow.com/questions/31666247/what-is-the-difference-between-the-nick-username-and-real-name-in-irc-and-wha>
     */
    username: Str,
    realname: Str,
    enabled_capabilities: Capabilities,
}

async fn handle_socket(
    config: ServerConfig,
    mut stream: TcpStream,
    socket_addr: &SocketAddr,
    core: LavinaCore,
    termination: Deferred<()>, // TODO use it to stop the connection gracefully
) -> Result<()> {
    log::info!("Received an IRC connection from {socket_addr}");
    let (reader, writer) = stream.split();
    let mut reader: BufReader<ReadHalf> = BufReader::new(reader);
    let mut writer = BufWriter::new(writer);

    pin!(termination);
    select! {
        biased;
        _ = &mut termination =>{
            log::info!("Socket handling was terminated");
            return Ok(())
        },
        registered_user = handle_registration(&mut reader, &mut writer, &core, &config) =>
            match registered_user {
                Ok(user) => {
                    log::debug!("User registered");
                    handle_registered_socket(config, &core, &mut reader, &mut writer, user).await?;
                }
                Err(err) => {
                    log::debug!("Registration failed: {err}");
                }
            }
    }
    stream.shutdown().await?;
    Ok(())
}

struct RegistrationState {
    /// The last received `NICK` message.
    future_nickname: Option<Str>,
    /// The last received `USER` message.
    future_username: Option<(Str, Str)>,
    enabled_capabilities: Capabilities,
    /// `CAP LS` or `CAP REQ` was received, but not `CAP END`.
    cap_negotiation_in_progress: bool,
    /// The last received `PASS` message.
    pass: Option<Str>,
    authentication_started: bool,
    validated_user: Option<Str>,
}

impl RegistrationState {
    fn new() -> RegistrationState {
        RegistrationState {
            future_nickname: None,
            future_username: None,
            enabled_capabilities: Capabilities::None,
            cap_negotiation_in_progress: false,
            pass: None,
            authentication_started: false,
            validated_user: None,
        }
    }

    /// Handle an incoming message from the client during the registration process.
    ///
    /// Returns `Some` if the user is fully registered, `None` if the registration is still in progress.
    async fn handle_msg(
        &mut self,
        msg: ClientMessage,
        writer: &mut BufWriter<WriteHalf<'_>>,
        core: &LavinaCore,
        config: &ServerConfig,
    ) -> Result<Option<RegisteredUser>> {
        match msg {
            ClientMessage::Pass { password } => {
                self.pass = Some(password);
                Ok(None)
            }
            ClientMessage::Capability { subcommand } => match subcommand {
                CapabilitySubcommand::List { code: _ } => {
                    self.cap_negotiation_in_progress = true;
                    ServerMessage {
                        tags: vec![],
                        sender: Some(config.server_name.clone().into()),
                        body: ServerMessageBody::Cap {
                            target: self.future_nickname.clone().unwrap_or_else(|| "*".into()),
                            subcmd: CapSubBody::Ls("sasl=PLAIN server-time".into()),
                        },
                    }
                    .write_async(writer)
                    .await?;
                    writer.flush().await?;
                    Ok(None)
                }
                CapabilitySubcommand::Req(caps) => {
                    self.cap_negotiation_in_progress = true;
                    let mut acked = vec![];
                    let mut naked = vec![];
                    for cap in caps {
                        if &*cap.name == "sasl" {
                            if cap.to_disable {
                                self.enabled_capabilities &= !Capabilities::Sasl;
                            } else {
                                self.enabled_capabilities |= Capabilities::Sasl;
                            }
                            acked.push(cap);
                        } else if &*cap.name == "server-time" {
                            if cap.to_disable {
                                self.enabled_capabilities &= !Capabilities::ServerTime;
                            } else {
                                self.enabled_capabilities |= Capabilities::ServerTime;
                            }
                            acked.push(cap);
                        } else {
                            naked.push(cap);
                        }
                    }
                    let mut ack_body = String::new();
                    if let Some((first, tail)) = acked.split_first() {
                        if first.to_disable {
                            ack_body.push('-');
                        }
                        ack_body += &*first.name;
                        for cap in tail {
                            ack_body.push(' ');
                            if cap.to_disable {
                                ack_body.push('-');
                            }
                            ack_body += &*cap.name;
                        }
                    }
                    ServerMessage {
                        tags: vec![],
                        sender: Some(config.server_name.clone().into()),
                        body: ServerMessageBody::Cap {
                            target: self.future_nickname.clone().unwrap_or_else(|| "*".into()),
                            subcmd: CapSubBody::Ack(ack_body.into()),
                        },
                    }
                    .write_async(writer)
                    .await?;
                    writer.flush().await?;
                    Ok(None)
                }
                CapabilitySubcommand::End => {
                    let Some((ref username, ref realname)) = self.future_username else {
                        self.cap_negotiation_in_progress = false;
                        return Ok(None);
                    };
                    let Some(nickname) = self.future_nickname.clone() else {
                        self.cap_negotiation_in_progress = false;
                        return Ok(None);
                    };
                    let username = username.clone();
                    let realname = realname.clone();
                    let candidate_user = RegisteredUser {
                        nickname: nickname.clone(),
                        username,
                        realname,
                        enabled_capabilities: self.enabled_capabilities,
                    };
                    self.finalize_auth(candidate_user, writer, core, config).await
                }
            },
            ClientMessage::Nick { nickname } => {
                if self.cap_negotiation_in_progress {
                    self.future_nickname = Some(nickname);
                    Ok(None)
                } else if let Some((username, realname)) = &self.future_username.clone() {
                    let candidate_user = RegisteredUser {
                        nickname: nickname.clone(),
                        username: username.clone(),
                        realname: realname.clone(),
                        enabled_capabilities: self.enabled_capabilities,
                    };
                    self.finalize_auth(candidate_user, writer, core, config).await
                } else {
                    self.future_nickname = Some(nickname);
                    Ok(None)
                }
            }
            ClientMessage::User { username, realname } => {
                if self.cap_negotiation_in_progress {
                    self.future_username = Some((username, realname));
                    Ok(None)
                } else if let Some(nickname) = self.future_nickname.clone() {
                    let candidate_user = RegisteredUser {
                        nickname: nickname.clone(),
                        username,
                        realname,
                        enabled_capabilities: self.enabled_capabilities,
                    };
                    self.finalize_auth(candidate_user, writer, core, config).await
                } else {
                    self.future_username = Some((username, realname));
                    Ok(None)
                }
            }
            ClientMessage::Authenticate(body) => {
                if !self.authentication_started {
                    tracing::debug!("Received authentication request");
                    if &*body == "PLAIN" {
                        tracing::debug!("Authentication request with method PLAIN");
                        self.authentication_started = true;
                        ServerMessage {
                            tags: vec![],
                            sender: Some(config.server_name.clone().into()),
                            body: ServerMessageBody::Authenticate("+".into()),
                        }
                        .write_async(writer)
                        .await?;
                        writer.flush().await?;
                        Ok(None)
                    } else {
                        let target = self.future_nickname.clone().unwrap_or_else(|| "*".into());
                        sasl_fail_message(config.server_name.clone(), target, "Unsupported mechanism".into())
                            .write_async(writer)
                            .await?;
                        writer.flush().await?;
                        Ok(None)
                    }
                } else {
                    let body = AuthBody::from_str(body.as_bytes())?;
                    if let Err(e) = auth_user(core, &body.login, &body.password).await {
                        tracing::warn!("Authentication failed: {:?}", e);
                        let target = self.future_nickname.clone().unwrap_or_else(|| "*".into());
                        sasl_fail_message(config.server_name.clone(), target, "Bad credentials".into())
                            .write_async(writer)
                            .await?;
                        writer.flush().await?;
                        Ok(None)
                    } else {
                        let login: Str = body.login.into();
                        self.validated_user = Some(login.clone());
                        ServerMessage {
                            tags: vec![],
                            sender: Some(config.server_name.clone().into()),
                            body: ServerMessageBody::N900LoggedIn {
                                nick: login.clone(),
                                address: login.clone(),
                                account: login.clone(),
                                message: format!("You are now logged in as {}", login).into(),
                            },
                        }
                        .write_async(writer)
                        .await?;
                        ServerMessage {
                            tags: vec![],
                            sender: Some(config.server_name.clone().into()),
                            body: ServerMessageBody::N903SaslSuccess {
                                nick: login.clone(),
                                message: "SASL authentication successful".into(),
                            },
                        }
                        .write_async(writer)
                        .await?;
                        writer.flush().await?;
                        Ok(None)
                    }
                }

                // TODO handle abortion of authentication
            }
            _ => Ok(None),
        }
    }

    async fn finalize_auth(
        &mut self,
        candidate_user: RegisteredUser,
        writer: &mut BufWriter<WriteHalf<'_>>,
        core: &LavinaCore,
        config: &ServerConfig,
    ) -> Result<Option<RegisteredUser>> {
        if self.enabled_capabilities.contains(Capabilities::Sasl)
            && self.validated_user.as_ref() == Some(&candidate_user.nickname)
        {
            Ok(Some(candidate_user))
        } else {
            let Some(candidate_password) = &self.pass else {
                sasl_fail_message(
                    config.server_name.clone(),
                    candidate_user.nickname.clone(),
                    "User credentials was not provided".into(),
                )
                .write_async(writer)
                .await?;
                writer.flush().await?;
                return Ok(None);
            };
            auth_user(core, &*candidate_user.nickname, &*candidate_password).await?;
            Ok(Some(candidate_user))
        }
    }
}

async fn handle_registration<'a>(
    reader: &mut BufReader<ReadHalf<'a>>,
    writer: &mut BufWriter<WriteHalf<'a>>,
    core: &LavinaCore,
    config: &ServerConfig,
) -> Result<RegisteredUser> {
    let mut buffer = vec![];

    let mut state = RegistrationState::new();

    let user = loop {
        let res = read_irc_message(reader, &mut buffer).await;
        tracing::trace!("Received message: {:?}", res);
        let len = match res {
            Ok(len) => len,
            Err(err) => {
                log::warn!("Failed to read from socket: {err}");
                break Err(err.into());
            }
        };
        if len == 0 {
            log::info!("Terminating socket");
            break Err(anyhow::Error::msg("EOF"));
        }
        let res = match std::str::from_utf8(&buffer[..len - 2]) {
            Ok(res) => res,
            Err(e) => break Err(e.into()),
        };
        tracing::trace!("Incoming raw IRC message: '{res}'");
        let parsed = client_message(res);
        let msg = match parsed {
            Ok(msg) => msg,
            Err(err) => {
                tracing::warn!("Failed to parse IRC message: {err}");
                buffer.clear();
                continue;
            }
        };
        tracing::debug!("Incoming IRC message: {msg:?}");
        if let Some(user) = state.handle_msg(msg, writer, core, config).await? {
            break Ok(user);
        }
        buffer.clear();
    }?;
    // TODO properly implement session temination
    Ok(user)
}

fn sasl_fail_message(sender: Str, nick: Str, text: Str) -> ServerMessage {
    ServerMessage {
        tags: vec![],
        sender: Some(sender),
        body: ServerMessageBody::N904SaslFail { nick, text },
    }
}

async fn auth_user(core: &LavinaCore, login: &str, plain_password: &str) -> Result<()> {
    let verdict = core.authenticate(login, plain_password).await?;
    // TODO properly map these onto protocol messages
    match verdict {
        Verdict::Authenticated => Ok(()),
        Verdict::UserNotFound => Err(anyhow!("no user found")),
        Verdict::InvalidPassword => Err(anyhow!("incorrect credentials")),
    }
}

async fn handle_registered_socket<'a>(
    config: ServerConfig,
    core: &LavinaCore,
    reader: &mut BufReader<ReadHalf<'a>>,
    writer: &mut BufWriter<WriteHalf<'a>>,
    user: RegisteredUser,
) -> Result<()> {
    let mut buffer = vec![];
    log::info!("Handling registered user: {user:?}");

    let player_id = PlayerId::from(user.nickname.clone())?;
    let mut connection = core.connect_to_player(&player_id).await;
    let text: Str = format!("Welcome to {} Server", &config.server_name).into();

    ServerMessage {
        tags: vec![],
        sender: Some(config.server_name.clone()),
        body: ServerMessageBody::N001Welcome {
            client: user.nickname.clone(),
            text: text.clone(),
        },
    }
    .write_async(writer)
    .await?;
    ServerMessage {
        tags: vec![],
        sender: Some(config.server_name.clone()),
        body: ServerMessageBody::N002YourHost {
            client: user.nickname.clone(),
            text: text.clone(),
        },
    }
    .write_async(writer)
    .await?;
    ServerMessage {
        tags: vec![],
        sender: Some(config.server_name.clone()),
        body: ServerMessageBody::N003Created {
            client: user.nickname.clone(),
            text: text.clone(),
        },
    }
    .write_async(writer)
    .await?;
    ServerMessage {
        tags: vec![],
        sender: Some(config.server_name.clone()),
        body: ServerMessageBody::N004MyInfo {
            client: user.nickname.clone(),
            hostname: config.server_name.clone(),
            softname: APP_VERSION.into(),
        },
    }
    .write_async(writer)
    .await?;
    ServerMessage {
        tags: vec![],
        sender: Some(config.server_name.clone()),
        body: ServerMessageBody::N005ISupport {
            client: user.nickname.clone(),
            params: "CHANTYPES=#".into(),
        },
    }
    .write_async(writer)
    .await?;

    let rooms_list = connection.get_rooms().await?;
    for room in &rooms_list {
        produce_on_join_cmd_messages(&config, &user, &Chan::Global(room.id.as_inner().clone()), room, writer).await?;
    }

    writer.flush().await?;

    loop {
        select! {
            biased;
            len = read_irc_message(reader, &mut buffer) => {
                let len = len?;
                let len = if len == 0 {
                    log::info!("EOF, Terminating socket");
                    break;
                } else {
                    len
                };
                let incoming = std::str::from_utf8(&buffer[0..len-2])?;
                if let HandleResult::Leave = handle_incoming_message(incoming, &config, &user, core, &mut connection, writer).await? {
                    break;
                }
                buffer.clear();
            },
            update = connection.receiver.recv() => {
                match update {
                    Some(ConnectionMessage::Update(update)) => {
                        handle_update(&config, &user, &player_id, writer, core, update).await?;
                    }
                    Some(ConnectionMessage::Stop(_)) => {
                        tracing::debug!("Connection is being terminated");
                        break;
                    }
                    None => {
                        log::warn!("Player is terminated, must terminate the connection");
                        break;
                    }
                }
            }
        }
    }
    ServerMessage {
        tags: vec![],
        sender: Some(config.server_name.clone()),
        body: ServerMessageBody::Error {
            reason: "Leaving the server".into(),
        },
    }
    .write_async(writer)
    .await?;
    writer.flush().await?;

    connection.terminate().await;
    Ok(())
}

// TODO this is public only for tests, perhaps move this into proto-irc
// TODO limit buffer size in size to protect against dos attacks with large payloads
pub async fn read_irc_message(reader: &mut BufReader<ReadHalf<'_>>, buf: &mut Vec<u8>) -> Result<usize> {
    let mut size = 0;
    'outer: loop {
        let res = reader.read_until(b'\r', buf).await?;
        size += res;
        let next = reader.read_u8().await?;
        buf.push(next);
        size += 1;
        if next != b'\n' {
            continue 'outer;
        }
        return Ok(size);
    }
}

async fn handle_update(
    config: &ServerConfig,
    user: &RegisteredUser,
    player_id: &PlayerId,
    writer: &mut (impl AsyncWrite + Unpin),
    core: &LavinaCore,
    update: Updates,
) -> Result<()> {
    log::debug!("Sending irc message to player {player_id:?} on update {update:?}");
    match update {
        Updates::RoomJoined { new_member_id, room_id } => {
            if player_id == &new_member_id {
                if let Some(room) = core.get_room(&room_id).await {
                    let room_info = room.get_room_info().await;
                    let chan = Chan::Global(room_id.as_inner().clone());
                    produce_on_join_cmd_messages(&config, &user, &chan, &room_info, writer).await?;
                    writer.flush().await?;
                } else {
                    log::warn!("Received join to a non-existant room");
                }
            } else {
                ServerMessage {
                    tags: vec![],
                    sender: Some(new_member_id.as_inner().clone()),
                    body: ServerMessageBody::Join(Chan::Global(room_id.as_inner().clone())),
                }
                .write_async(writer)
                .await?;
                writer.flush().await?
            }
        }
        Updates::RoomLeft {
            room_id,
            former_member_id,
        } => {
            ServerMessage {
                tags: vec![],
                sender: Some(former_member_id.as_inner().clone()),
                body: ServerMessageBody::Part(Chan::Global(room_id.as_inner().clone())),
            }
            .write_async(writer)
            .await?;
            writer.flush().await?
        }
        Updates::NewMessage {
            author_id,
            room_id,
            body,
            created_at,
        } => {
            let mut tags = vec![];
            if user.enabled_capabilities.contains(Capabilities::ServerTime) {
                let tag = Tag {
                    key: "time".into(),
                    value: Some(created_at.to_rfc3339_opts(SecondsFormat::Millis, true).into()),
                };
                tags.push(tag);
            }
            ServerMessage {
                tags,
                sender: Some(author_id.as_inner().clone()),
                body: ServerMessageBody::PrivateMessage {
                    target: Recipient::Chan(Chan::Global(room_id.as_inner().clone())),
                    body: body.clone(),
                },
            }
            .write_async(writer)
            .await?;
            writer.flush().await?
        }
        Updates::RoomTopicChanged { room_id, new_topic } => {
            ServerMessage {
                tags: vec![],
                sender: Some(config.server_name.clone()),
                body: ServerMessageBody::N332Topic {
                    client: user.nickname.clone(),
                    chat: Chan::Global(room_id.as_inner().clone()),
                    topic: new_topic,
                },
            }
            .write_async(writer)
            .await?;
            writer.flush().await?
        }
        Updates::BannedFrom(room_id) => {
            // TODO think about the case when the user was banned, but was not in the room - no need to send PART in this case
            ServerMessage {
                tags: vec![],
                sender: Some(player_id.as_inner().clone()),
                body: ServerMessageBody::Part(Chan::Global(room_id.as_inner().clone())),
            }
            .write_async(writer)
            .await?;
            writer.flush().await?
        }
        Updates::NewDialogMessage {
            sender,
            receiver,
            body,
            created_at,
        } => {
            let mut tags = vec![];
            if user.enabled_capabilities.contains(Capabilities::ServerTime) {
                let tag = Tag {
                    key: "time".into(),
                    value: Some(created_at.to_rfc3339_opts(SecondsFormat::Millis, true).into()),
                };
                tags.push(tag);
            }
            ServerMessage {
                tags,
                sender: Some(sender.as_inner().clone()),
                body: ServerMessageBody::PrivateMessage {
                    target: Recipient::Nick(receiver.as_inner().clone()),
                    body: body.clone(),
                },
            }
            .write_async(writer)
            .await?;
            writer.flush().await?
        }
    }
    Ok(())
}

enum HandleResult {
    Continue,
    Leave,
}

#[tracing::instrument(skip_all, name = "handle_incoming_message")]
async fn handle_incoming_message(
    buffer: &str,
    config: &ServerConfig,
    user: &RegisteredUser,
    core: &LavinaCore,
    user_handle: &mut PlayerConnection,
    writer: &mut (impl AsyncWrite + Unpin),
) -> Result<HandleResult> {
    log::debug!("Incoming raw IRC message: '{buffer}'");
    let parsed = client_message(buffer);
    log::debug!("Incoming IRC message: {parsed:?}");
    match parsed {
        Ok(msg) => match msg {
            ClientMessage::Ping { token } => {
                ServerMessage {
                    tags: vec![],
                    sender: Some(config.server_name.clone()),
                    body: ServerMessageBody::Pong {
                        from: config.server_name.clone(),
                        token,
                    },
                }
                .write_async(writer)
                .await?;
                writer.flush().await?;
            }
            ClientMessage::Join(ref chan) => {
                handle_join(&config, &user, user_handle, chan, writer).await?;
            }
            ClientMessage::Part { chan, message } => {
                handle_part(config, user, user_handle, &chan, writer).await?;
            }
            ClientMessage::PrivateMessage { recipient, body } => match recipient {
                Recipient::Chan(Chan::Global(chan)) => {
                    let room_id = RoomId::from(chan)?;
                    user_handle.send_message(room_id, body).await?;
                }
                Recipient::Nick(nick) => {
                    let receiver = PlayerId::from(nick)?;
                    user_handle.send_dialog_message(receiver, body).await?;
                }
                _ => log::warn!("Unsupported target type"),
            },
            ClientMessage::Topic { chan, topic } => {
                match chan {
                    Chan::Global(chan) => {
                        let room_id = RoomId::from(chan)?;
                        user_handle.change_topic(room_id.clone(), topic.clone()).await?;
                        ServerMessage {
                            tags: vec![],
                            sender: Some(config.server_name.clone()),
                            body: ServerMessageBody::N332Topic {
                                client: user.nickname.clone(),
                                chat: Chan::Global(room_id.as_inner().clone()),
                                topic,
                            },
                        }
                        .write_async(writer)
                        .await?;
                        writer.flush().await?;
                    }
                    Chan::Local(_) => {}
                };
            }
            ClientMessage::Who { target } => match &target {
                Recipient::Nick(nick) => {
                    // TODO handle non-existing user
                    ServerMessage {
                        tags: vec![],
                        sender: Some(config.server_name.clone()),
                        body: user_to_who_msg(config, user, nick),
                    }
                    .write_async(writer)
                    .await?;
                    ServerMessage {
                        tags: vec![],
                        sender: Some(config.server_name.clone()),
                        body: ServerMessageBody::N315EndOfWho {
                            client: user.nickname.clone(),
                            mask: target.clone(),
                            msg: "End of WHO list".into(),
                        },
                    }
                    .write_async(writer)
                    .await?;
                    writer.flush().await?;
                }
                Recipient::Chan(Chan::Global(chan)) => {
                    let room = core.get_room(&RoomId::from(chan.clone())?).await;
                    if let Some(room) = room {
                        let room_info = room.get_room_info().await;
                        for member in room_info.members {
                            ServerMessage {
                                tags: vec![],
                                sender: Some(config.server_name.clone()),
                                body: user_to_who_msg(config, user, member.as_inner()),
                            }
                            .write_async(writer)
                            .await?;
                        }
                    }
                    ServerMessage {
                        tags: vec![],
                        sender: Some(config.server_name.clone()),
                        body: ServerMessageBody::N315EndOfWho {
                            client: user.nickname.clone(),
                            mask: target.clone(),
                            msg: "End of WHO list".into(),
                        },
                    }
                    .write_async(writer)
                    .await?;
                    writer.flush().await?;
                }
                Recipient::Chan(Chan::Local(_)) => {
                    log::warn!("Local chans not supported");
                }
            },
            ClientMessage::Whois { arg } => {
                arg.handle(handler::IrcConnection {
                    server_name: config.server_name.clone(),
                    client: user.nickname.clone(),
                    writer,
                    player_connection: user_handle,
                })
                .await?;

                writer.flush().await?;
            }
            ClientMessage::Mode { target } => {
                match target {
                    Recipient::Nick(nickname) => {
                        if nickname == user.nickname {
                            ServerMessage {
                                tags: vec![],
                                sender: Some(config.server_name.clone()),
                                body: ServerMessageBody::N221UserModeIs {
                                    client: user.nickname.clone(),
                                    modes: "+r".into(),
                                },
                            }
                            .write_async(writer)
                            .await?;
                            writer.flush().await?;
                        } else {
                            ServerMessage {
                                tags: vec![],
                                sender: Some(config.server_name.clone()),
                                body: ServerMessageBody::N502UsersDontMatch {
                                    client: user.nickname.clone(),
                                    message: "Cant change mode for other users".into(),
                                },
                            }
                            .write_async(writer)
                            .await?;
                            writer.flush().await?;
                        }
                    }
                    Recipient::Chan(_) => {
                        // TODO handle chan mode handling
                    }
                }
            }
            ClientMessage::Quit { reason } => {
                log::info!("Received QUIT");
                return Ok(HandleResult::Leave);
            }
            cmd => {
                log::warn!("Not implemented handler for client command: {cmd:?}");
            }
        },
        Err(err) => {
            log::warn!("Failed to parse IRC message: {err}");
        }
    }
    Ok(HandleResult::Continue)
}

fn user_to_who_msg(config: &ServerConfig, requestor: &RegisteredUser, target_user_nickname: &Str) -> ServerMessageBody {
    // Username is equal to nickname
    let username = format!("~{target_user_nickname}").into();

    // User's host is not public, replace it with `user/<nickname>` pattern
    let host = format!("user/{target_user_nickname}").into();

    ServerMessageBody::N352WhoReply {
        client: requestor.nickname.clone(),
        username,
        host,
        server: config.server_name.clone(),
        flags: AwayStatus::Here,
        nickname: target_user_nickname.clone(),
        hops: 0,
        // TODO Realname is not available yet, should be matched to a future core's player field
        realname: target_user_nickname.clone(),
    }
}

async fn handle_join(
    config: &ServerConfig,
    user: &RegisteredUser,
    user_handle: &mut PlayerConnection,
    chan: &Chan,
    writer: &mut (impl AsyncWrite + Unpin),
) -> Result<()> {
    match chan {
        Chan::Global(chan_name) => {
            let room_id = RoomId::from(chan_name.clone())?;
            if let JoinResult::Success(room_info) = user_handle.join_room(room_id).await? {
                produce_on_join_cmd_messages(&config, &user, chan, &room_info, writer).await?;
            } else {
                ServerMessage {
                    tags: vec![],
                    sender: Some(config.server_name.clone()),
                    body: ServerMessageBody::N474BannedFromChan {
                        client: user.nickname.clone(),
                        chan: chan.clone(),
                        message: "U dun goofed".into(),
                    },
                }
                .write_async(writer)
                .await?;
            }
            writer.flush().await?;
        }
        Chan::Local(_) => {}
    };
    Ok(())
}

async fn handle_part(
    config: &ServerConfig,
    user: &RegisteredUser,
    user_handle: &mut PlayerConnection,
    chan: &Chan,
    writer: &mut (impl AsyncWrite + Unpin),
) -> Result<()> {
    if let Chan::Global(chan_name) = chan {
        let room_id = RoomId::from(chan_name.clone())?;
        user_handle.leave_room(room_id).await?;
        ServerMessage {
            tags: vec![],
            sender: Some(user.nickname.clone()),
            body: ServerMessageBody::Part(Chan::Global(chan_name.clone())),
        }
        .write_async(writer)
        .await?;
        writer.flush().await?;
    } else {
        log::warn!("Local chans unsupported");
    }
    Ok(())
}

async fn produce_on_join_cmd_messages(
    config: &ServerConfig,
    user: &RegisteredUser,
    chan: &Chan,
    room_info: &RoomInfo,
    writer: &mut (impl AsyncWrite + Unpin),
) -> Result<()> {
    ServerMessage {
        tags: vec![],
        sender: Some(user.nickname.clone()),
        body: ServerMessageBody::Join(chan.clone()),
    }
    .write_async(writer)
    .await?;
    ServerMessage {
        tags: vec![],
        sender: Some(config.server_name.clone()),
        body: ServerMessageBody::N332Topic {
            client: user.nickname.clone(),
            chat: chan.clone(),
            topic: room_info.topic.clone(),
        },
    }
    .write_async(writer)
    .await?;
    let prefixed_members: Vec<PrefixedNick> =
        room_info.members.iter().map(|member| PrefixedNick::from_str(member.clone().into_inner())).collect();
    let non_empty_members: NonEmpty<PrefixedNick> =
        NonEmpty::from_vec(prefixed_members).unwrap_or(nonempty![PrefixedNick::from_str(user.nickname.clone())]);

    ServerMessage {
        tags: vec![],
        sender: Some(config.server_name.clone()),
        body: ServerMessageBody::N353NamesReply {
            client: user.nickname.clone(),
            chan: chan.clone(),
            members: non_empty_members.into(),
        },
    }
    .write_async(writer)
    .await?;
    ServerMessage {
        tags: vec![],
        sender: Some(config.server_name.clone()),
        body: ServerMessageBody::N366NamesReplyEnd {
            client: user.nickname.clone(),
            chan: chan.clone(),
        },
    }
    .write_async(writer)
    .await?;
    Ok(())
}

pub struct RunningServer {
    pub addr: SocketAddr,
    terminator: Terminator,
}

impl RunningServer {
    pub async fn terminate(self) -> Result<()> {
        self.terminator.terminate().await
    }
}

pub async fn launch(config: ServerConfig, core: LavinaCore, metrics: MetricsRegistry) -> Result<RunningServer> {
    log::info!("Starting IRC projection");
    let (stopped_tx, mut stopped_rx) = channel(32);
    let current_connections = IntGauge::new("irc_current_connections", "Open and alive TCP connections")?;
    let total_connections = IntCounter::new("irc_total_connections", "Total number of opened connections")?;
    metrics.register(Box::new(current_connections.clone()))?;
    metrics.register(Box::new(total_connections.clone()))?;

    let listener = TcpListener::bind(config.listen_on).await?;
    let addr = listener.local_addr()?;

    let terminator = Terminator::spawn(|mut rx| async move {
        // TODO probably should separate logic for accepting new connection and storing them
        // into two tasks so that they don't block each other
        let mut actors = HashMap::new();
        loop {
            select! {
                biased;
                _ = &mut rx => break,
                stopped = stopped_rx.recv() => match stopped {
                    Some(stopped) => { let _ = actors.remove(&stopped); },
                    None => unreachable!(),
                },
                new_conn = listener.accept() => {
                    match new_conn {
                        Ok((stream, socket_addr)) => {
                            let config = config.clone();
                            total_connections.inc();
                            current_connections.inc();
                            log::debug!("Incoming connection from {socket_addr}");

                            if actors.contains_key(&socket_addr) {
                                log::warn!("Already contains connection form {socket_addr}");
                                // TODO kill the older connection and restart it
                                continue;
                            }

                            let terminator = Terminator::spawn(|termination| {
                                let core = core.clone();
                                let current_connections_clone = current_connections.clone();
                                let stopped_tx = stopped_tx.clone();
                                async move {
                                    match handle_socket(config, stream, &socket_addr, core, termination).await {
                                        Ok(_) => log::info!("Connection terminated"),
                                        Err(err) => log::warn!("Connection failed: {err}"),
                                    }
                                    current_connections_clone.dec();
                                    stopped_tx.send(socket_addr).await?;
                                    Ok(())
                                }
                            });
                            actors.insert(socket_addr, terminator);
                        },
                        Err(err) => log::warn!("Failed to accept new connection: {err}"),
                    }
                },
            }
        }

        log::info!("Stopping IRC projection");
        join_all(actors.into_iter().map(|(socket_addr, terminator)| async move {
            log::debug!("Stopping IRC connection at {socket_addr}");
            match terminator.terminate().await {
                Ok(_) => log::debug!("Stopped IRC connection at {socket_addr}"),
                Err(err) => {
                    log::warn!("IRC connection to {socket_addr} finished with error: {err}")
                }
            }
        }))
        .await;
        log::info!("Stopped IRC projection");
        Ok(())
    });

    log::info!("Started IRC projection");
    Ok(RunningServer { addr, terminator })
}