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

use futures_util::future::join_all;
use prometheus::{IntCounter, IntGauge, Registry as MetricsRegistry};
use serde::Deserialize;
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 crate::core::player::*;
use crate::core::room::{RoomId, RoomInfo, RoomRegistry};
use crate::prelude::*;
use crate::protos::irc::client::{client_message, ClientMessage};
use crate::protos::irc::server::{AwayStatus, ServerMessage, ServerMessageBody};
use crate::protos::irc::{Chan, Recipient};
use crate::util::Terminator;

#[cfg(test)]
mod test;

#[derive(Deserialize, Debug, Clone)]
pub struct ServerConfig {
    pub listen_on: SocketAddr,
    pub server_name: Box<str>,
}

#[derive(Debug)]
struct RegisteredUser {
    nickname: Box<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: Box<str>,
    realname: Box<str>,
}

async fn handle_socket(
    config: ServerConfig,
    mut stream: TcpStream,
    socket_addr: &SocketAddr,
    players: PlayerRegistry,
    rooms: RoomRegistry,
    termination: Deferred<()>, // TODO use it to stop the connection gracefully
) -> Result<()> {
    let (reader, writer) = stream.split();
    let mut reader: BufReader<ReadHalf> = BufReader::new(reader);
    let mut writer = BufWriter::new(writer);

    ServerMessage {
        tags: vec![],
        sender: Some(config.server_name.clone().into()),
        body: ServerMessageBody::Notice {
            first_target: "*".into(),
            rest_targets: vec![],
            text: "Welcome to my server!".into(),
        },
    }
    .write_async(&mut writer)
    .await?;
    writer.flush().await?;

    let registered_user: Result<RegisteredUser> =
        handle_registration(&mut reader, &mut writer).await;
    match registered_user {
        Ok(user) => {
            handle_registered_socket(config, players, rooms, &mut reader, &mut writer, user)
                .await?;
        }
        Err(_) => {}
    }

    stream.shutdown().await?;
    Ok(())
}

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

    let mut future_nickname: Option<Box<str>> = None;
    let mut future_username: Option<(Box<str>, Box<str>)> = None;

    loop {
        let res = reader.read_until(b'\n', &mut buffer).await;
        let res = match res {
            Ok(len) => {
                if len == 0 {
                    log::info!("Terminating socket");
                    break Err(anyhow::Error::msg("EOF"));
                }
                match std::str::from_utf8(&buffer[..len]) {
                    Ok(res) => res,
                    Err(e) => break Err(e.into()),
                }
            }
            Err(err) => {
                log::warn!("Failed to read from socket: {err}");
                break Err(err.into());
            }
        };
        let parsed = client_message(res);
        match parsed {
            Ok((_, msg)) => {
                log::info!("Incoming IRC message: {msg:?}");
                match msg {
                    ClientMessage::Nick { nickname } => {
                        if let Some((username, realname)) = future_username {
                            break Ok(RegisteredUser {
                                nickname,
                                username,
                                realname,
                            });
                        } else {
                            future_nickname = Some(nickname);
                        }
                    }
                    ClientMessage::User { username, realname } => {
                        if let Some(nickname) = future_nickname {
                            break Ok(RegisteredUser {
                                nickname,
                                username,
                                realname,
                            });
                        } else {
                            future_username = Some((username, realname));
                        }
                    }
                    _ => {}
                }
            }
            Err(err) => {
                log::warn!("Failed to parse IRC message: {err}");
            }
        }
        buffer.clear();
    }
}

async fn handle_registered_socket<'a>(
    config: ServerConfig,
    mut players: PlayerRegistry,
    rooms: RoomRegistry,
    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_bytes(user.nickname.clone())?;
    let mut connection = players.connect_to_player(player_id.clone()).await;

    ServerMessage {
        tags: vec![],
        sender: Some(config.server_name.clone()),
        body: ServerMessageBody::N001Welcome {
            client: user.nickname.clone(),
            text: "Welcome to Kek Server".into(),
        },
    }
    .write_async(writer)
    .await?;
    ServerMessage {
        tags: vec![],
        sender: Some(config.server_name.clone()),
        body: ServerMessageBody::N002YourHost {
            client: user.nickname.clone(),
            text: "Welcome to Kek Server".into(),
        },
    }
    .write_async(writer)
    .await?;
    ServerMessage {
        tags: vec![],
        sender: Some(config.server_name.clone()),
        body: ServerMessageBody::N003Created {
            client: user.nickname.clone(),
            text: "Welcome to Kek Server".into(),
        },
    }
    .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: "kek-0.1.alpha.3".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_bytes().clone()),
            room,
            writer,
        )
        .await?;
    }

    writer.flush().await?;

    loop {
        select! {
            biased;
            len = reader.read_until(b'\n', &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])?;
                if let HandleResult::Leave = handle_incoming_message(incoming, &config, &user, &rooms, &mut connection, writer).await? {
                    break;
                }
                buffer.clear();
            },
            update = connection.receiver.recv() => {
                if let Some(update) = update {
                    handle_update(&config, &user, &player_id, writer, &rooms, update).await?;
                } else {
                    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(())
}

async fn handle_update(
    config: &ServerConfig,
    user: &RegisteredUser,
    player_id: &PlayerId,
    writer: &mut (impl AsyncWrite + Unpin),
    rooms: &RoomRegistry,
    update: Updates,
) -> Result<()> {
    match update {
        Updates::RoomJoined {
            new_member_id,
            room_id,
        } => {
            if player_id == &new_member_id {
                if let Some(room) = rooms.get_room(&room_id) {
                    let room_info = room.get_room_info().await;
                    let chan = Chan::Global(room_id.as_bytes().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_bytes().clone()),
                    body: ServerMessageBody::Join(Chan::Global(room_id.as_bytes().clone())),
                }
                .write_async(writer)
                .await?;
                writer.flush().await?
            }
        }
        Updates::RoomLeft {
            room_id,
            former_member_id,
        } => {
            ServerMessage {
                tags: vec![],
                sender: Some(former_member_id.as_bytes().clone()),
                body: ServerMessageBody::Part(Chan::Global(room_id.as_bytes().clone())),
            }
            .write_async(writer)
            .await?;
            writer.flush().await?
        }
        Updates::NewMessage {
            author_id,
            room_id,
            body,
        } => {
            ServerMessage {
                tags: vec![],
                sender: Some(author_id.as_bytes().clone()),
                body: ServerMessageBody::PrivateMessage {
                    target: Recipient::Chan(Chan::Global(room_id.as_bytes().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_bytes().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_bytes().clone()),
                body: ServerMessageBody::Part(Chan::Global(room_id.as_bytes().clone())),
            }
            .write_async(writer)
            .await?;
            writer.flush().await?
        }
    }
    Ok(())
}

enum HandleResult {
    Continue,
    Leave,
}

async fn handle_incoming_message(
    buffer: &str,
    config: &ServerConfig,
    user: &RegisteredUser,
    rooms: &RoomRegistry,
    user_handle: &mut PlayerConnection,
    writer: &mut (impl AsyncWrite + Unpin),
) -> Result<HandleResult> {
    let parsed = client_message(buffer);
    match parsed {
        Ok((_, msg)) => match msg {
            ClientMessage::Ping { token } => {
                ServerMessage {
                    tags: vec![],
                    sender: None,
                    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_bytes(chan)?;
                    user_handle.send_message(room_id, body).await?;
                },
                _ => log::warn!("Unsupported target type"),
            },
            ClientMessage::Topic { chan, topic } => {
                match chan {
                    Chan::Global(chan) => {
                        let room_id = RoomId::from_bytes(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_bytes().clone()),
                                topic,
                            },
                        }
                        .write_async(writer)
                        .await?;
                        writer.flush().await?;
                    }
                    Chan::Local(_) => {}
                };
            }
            ClientMessage::Who { target } => match &target {
                Recipient::Nick(nick) => {
                    // TODO handle non-existing user
                    let mut username = format!("~{nick}");
                    let mut host = format!("user/{nick}");
                    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 = rooms.get_room(&RoomId::from_bytes(chan.clone())?);
                    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_bytes()),
                            }
                            .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::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 {
                            // TODO send 502 (not 401) if the user is not the sender
                        }
                    }
                    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: &ByteVec,
) -> 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 mut 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_bytes(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_bytes(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 mut members: String = if let Some(head) = room_info.members.first() {
        head.as_bytes().clone()
    } else {
        user.nickname.clone()
    }.into();
    for i in &room_info.members[1..] {
        members.push(' ');
        members.push_str(i.as_bytes());
    }
    ServerMessage {
        tags: vec![],
        sender: Some(config.server_name.clone()),
        body: ServerMessageBody::N353NamesReply {
            client: user.nickname.clone(),
            chan: chan.clone(),
            members: 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 async fn launch(
    config: ServerConfig,
    players: PlayerRegistry,
    rooms: RoomRegistry,
    metrics: MetricsRegistry,
) -> Result<Terminator> {
    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 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 players = players.clone();
                                let rooms = rooms.clone();
                                let current_connections_clone = current_connections.clone();
                                let stopped_tx = stopped_tx.clone();
                                async move {
                                    match handle_socket(config, stream, &socket_addr, players, rooms, 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(terminator)
}