//! Domain of chat participants.
//!
//! Player is a single user account, which is used to participate in chats,
//! including sending messages, receiving messaged, retrieving history and running privileged actions.
//! A player corresponds to a single user account. Usually a person has only one account,
//! but it is possible to have multiple accounts for one person and therefore multiple player entities.
//!
//! A player actor is a serial handler of commands from a single player. It is preferable to run all per-player validations in the player actor,
//! so that they don't overload the room actor.
use std::{
    collections::{HashMap, HashSet},
    sync::{Arc, RwLock},
};

use prometheus::{IntGauge, Registry as MetricsRegistry};
use serde::Serialize;
use tokio::sync::mpsc::{channel, Receiver, Sender};

use crate::prelude::*;
use crate::room::{RoomHandle, RoomId, RoomInfo, RoomRegistry};
use crate::table::{AnonTable, Key as AnonKey};

/// Opaque player identifier. Cannot contain spaces, must be shorter than 32.
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize)]
pub struct PlayerId(Str);
impl PlayerId {
    pub fn from(str: impl Into<Str>) -> Result<PlayerId> {
        let bytes = str.into();
        if bytes.len() > 32 {
            return Err(fail("Nickname cannot be longer than 32 symbols"));
        }
        if bytes.contains(' ') {
            return Err(anyhow::Error::msg("Nickname cannot contain spaces"));
        }
        Ok(PlayerId(bytes))
    }
    pub fn as_inner(&self) -> &Str {
        &self.0
    }
    pub fn into_inner(self) -> Str {
        self.0
    }
}

/// Node-local identifier of a connection. It is used to address a connection within a player actor.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct ConnectionId(pub AnonKey);

/// Representation of an authenticated client connection.
/// The public API available to projections through which all client actions are executed.
///
/// The connection is used to send commands to the player actor and to receive updates that might be sent to the client.
pub struct PlayerConnection {
    pub connection_id: ConnectionId,
    pub receiver: Receiver<Updates>,
    player_handle: PlayerHandle,
}
impl PlayerConnection {
    /// Handled in [Player::send_message].
    pub async fn send_message(&mut self, room_id: RoomId, body: Str) -> Result<()> {
        let (promise, deferred) = oneshot();
        let cmd = ClientCommand::SendMessage { room_id, body, promise };
        self.player_handle.send(ActorCommand::ClientCommand(cmd, self.connection_id.clone())).await;
        Ok(deferred.await?)
    }

    /// Handled in [Player::join_room].
    pub async fn join_room(&mut self, room_id: RoomId) -> Result<JoinResult> {
        let (promise, deferred) = oneshot();
        let cmd = ClientCommand::JoinRoom { room_id, promise };
        self.player_handle.send(ActorCommand::ClientCommand(cmd, self.connection_id.clone())).await;
        Ok(deferred.await?)
    }

    /// Handled in [Player::change_topic].
    pub async fn change_topic(&mut self, room_id: RoomId, new_topic: Str) -> Result<()> {
        let (promise, deferred) = oneshot();
        let cmd = ClientCommand::ChangeTopic {
            room_id,
            new_topic,
            promise,
        };
        self.player_handle.send(ActorCommand::ClientCommand(cmd, self.connection_id.clone())).await;
        Ok(deferred.await?)
    }

    /// Handled in [Player::leave_room].
    pub async fn leave_room(&mut self, room_id: RoomId) -> Result<()> {
        let (promise, deferred) = oneshot();
        let cmd = ClientCommand::LeaveRoom { room_id, promise };
        self.player_handle.send(ActorCommand::ClientCommand(cmd, self.connection_id.clone())).await;
        Ok(deferred.await?)
    }

    pub async fn terminate(self) {
        self.player_handle.send(ActorCommand::TerminateConnection(self.connection_id)).await;
    }

    /// Handled in [Player::get_rooms].
    pub async fn get_rooms(&self) -> Result<Vec<RoomInfo>> {
        let (promise, deferred) = oneshot();
        let cmd = ClientCommand::GetRooms { promise };
        self.player_handle.send(ActorCommand::ClientCommand(cmd, self.connection_id.clone())).await;
        Ok(deferred.await?)
    }
}

/// Handle to a player actor.
#[derive(Clone)]
pub struct PlayerHandle {
    tx: Sender<ActorCommand>,
}
impl PlayerHandle {
    pub async fn subscribe(&self) -> PlayerConnection {
        let (sender, receiver) = channel(32);
        let (promise, deferred) = oneshot();
        let cmd = ActorCommand::AddConnection { sender, promise };
        let _ = self.tx.send(cmd).await;
        let connection_id = deferred.await.unwrap();
        PlayerConnection {
            connection_id,
            player_handle: self.clone(),
            receiver,
        }
    }

    async fn send(&self, command: ActorCommand) {
        // TODO either handle the error or doc why it is safe to ignore
        let _ = self.tx.send(command).await;
    }

    pub async fn update(&self, update: Updates) {
        self.send(ActorCommand::Update(update)).await;
    }
}

/// Messages sent to the player actor.
enum ActorCommand {
    /// Establish a new connection.
    AddConnection {
        sender: Sender<Updates>,
        promise: Promise<ConnectionId>,
    },
    /// Terminate an existing connection.
    TerminateConnection(ConnectionId),
    /// Player-issued command.
    ClientCommand(ClientCommand, ConnectionId),
    /// Update which is sent from a room the player is member of.
    Update(Updates),
    Stop,
}

/// Client-issued command sent to the player actor. The actor will respond with by fulfilling the promise.
pub enum ClientCommand {
    JoinRoom {
        room_id: RoomId,
        promise: Promise<JoinResult>,
    },
    LeaveRoom {
        room_id: RoomId,
        promise: Promise<()>,
    },
    SendMessage {
        room_id: RoomId,
        body: Str,
        promise: Promise<()>,
    },
    ChangeTopic {
        room_id: RoomId,
        new_topic: Str,
        promise: Promise<()>,
    },
    GetRooms {
        promise: Promise<Vec<RoomInfo>>,
    },
}

pub enum JoinResult {
    Success(RoomInfo),
    Banned,
}

/// Player update event type which is sent to a player actor and from there to a connection handler.
#[derive(Clone, Debug)]
pub enum Updates {
    RoomTopicChanged {
        room_id: RoomId,
        new_topic: Str,
    },
    NewMessage {
        room_id: RoomId,
        author_id: PlayerId,
        body: Str,
    },
    RoomJoined {
        room_id: RoomId,
        new_member_id: PlayerId,
    },
    RoomLeft {
        room_id: RoomId,
        former_member_id: PlayerId,
    },
    /// The player was banned from the room and left it immediately.
    BannedFrom(RoomId),
}

/// Handle to a player registry — a shared data structure containing information about players.
#[derive(Clone)]
pub struct PlayerRegistry(Arc<RwLock<PlayerRegistryInner>>);
impl PlayerRegistry {
    pub fn empty(room_registry: RoomRegistry, metrics: &mut MetricsRegistry) -> Result<PlayerRegistry> {
        let metric_active_players = IntGauge::new("chat_players_active", "Number of alive player actors")?;
        metrics.register(Box::new(metric_active_players.clone()))?;
        let inner = PlayerRegistryInner {
            room_registry,
            players: HashMap::new(),
            metric_active_players,
        };
        Ok(PlayerRegistry(Arc::new(RwLock::new(inner))))
    }

    pub async fn get_or_create_player(&mut self, id: PlayerId) -> PlayerHandle {
        let mut inner = self.0.write().unwrap();
        if let Some((handle, _)) = inner.players.get(&id) {
            handle.clone()
        } else {
            let (handle, fiber) = Player::launch(id.clone(), inner.room_registry.clone());
            inner.players.insert(id, (handle.clone(), fiber));
            inner.metric_active_players.inc();
            handle
        }
    }

    pub async fn connect_to_player(&mut self, id: PlayerId) -> PlayerConnection {
        let player_handle = self.get_or_create_player(id).await;
        player_handle.subscribe().await
    }

    pub async fn shutdown_all(&mut self) -> Result<()> {
        let mut inner = self.0.write().unwrap();
        for (i, (k, j)) in inner.players.drain() {
            k.send(ActorCommand::Stop).await;
            drop(k);
            j.await?;
            log::debug!("Player stopped #{i:?}")
        }
        log::debug!("All players stopped");
        Ok(())
    }
}

/// The player registry state representation.
struct PlayerRegistryInner {
    room_registry: RoomRegistry,
    players: HashMap<PlayerId, (PlayerHandle, JoinHandle<Player>)>,
    metric_active_players: IntGauge,
}

/// Player actor inner state representation.
struct Player {
    player_id: PlayerId,
    connections: AnonTable<Sender<Updates>>,
    my_rooms: HashMap<RoomId, RoomHandle>,
    banned_from: HashSet<RoomId>,
    rx: Receiver<ActorCommand>,
    handle: PlayerHandle,
    rooms: RoomRegistry,
}
impl Player {
    fn launch(player_id: PlayerId, rooms: RoomRegistry) -> (PlayerHandle, JoinHandle<Player>) {
        let (tx, rx) = channel(32);
        let handle = PlayerHandle { tx };
        let handle_clone = handle.clone();
        let player = Player {
            player_id,
            connections: AnonTable::new(),
            my_rooms: HashMap::new(),
            banned_from: HashSet::from([RoomId::from("Empty").unwrap()]),
            rx,
            handle,
            rooms,
        };
        let fiber = tokio::task::spawn(player.main_loop());
        (handle_clone, fiber)
    }

    async fn main_loop(mut self) -> Self {
        while let Some(cmd) = self.rx.recv().await {
            match cmd {
                ActorCommand::AddConnection { sender, promise } => {
                    let connection_id = self.connections.insert(sender);
                    if let Err(connection_id) = promise.send(ConnectionId(connection_id)) {
                        log::warn!("Connection {connection_id:?} terminated before finalization");
                        self.terminate_connection(connection_id);
                    }
                }
                ActorCommand::TerminateConnection(connection_id) => {
                    self.terminate_connection(connection_id);
                }
                ActorCommand::Update(update) => self.handle_update(update).await,
                ActorCommand::ClientCommand(cmd, connection_id) => self.handle_cmd(cmd, connection_id).await,
                ActorCommand::Stop => break,
            }
        }
        log::debug!("Shutting down player actor #{:?}", self.player_id);
        self
    }

    /// Handle an incoming update by changing the internal state and broadcasting it to all connections if necessary.
    async fn handle_update(&mut self, update: Updates) {
        log::info!(
            "Player received an update, broadcasting to {} connections",
            self.connections.len()
        );
        match update {
            Updates::BannedFrom(ref room_id) => {
                self.banned_from.insert(room_id.clone());
                self.my_rooms.remove(room_id);
            }
            _ => {}
        }
        for (_, connection) in &self.connections {
            let _ = connection.send(update.clone()).await;
        }
    }

    fn terminate_connection(&mut self, connection_id: ConnectionId) {
        if let None = self.connections.pop(connection_id.0) {
            log::warn!("Connection {connection_id:?} already terminated");
        }
    }

    /// Dispatches a client command to the appropriate handler.
    async fn handle_cmd(&mut self, cmd: ClientCommand, connection_id: ConnectionId) {
        match cmd {
            ClientCommand::JoinRoom { room_id, promise } => {
                let result = self.join_room(connection_id, room_id).await;
                let _ = promise.send(result);
            }
            ClientCommand::LeaveRoom { room_id, promise } => {
                self.leave_room(connection_id, room_id).await;
                let _ = promise.send(());
            }
            ClientCommand::SendMessage { room_id, body, promise } => {
                self.send_message(connection_id, room_id, body).await;
                let _ = promise.send(());
            }
            ClientCommand::ChangeTopic {
                room_id,
                new_topic,
                promise,
            } => {
                self.change_topic(connection_id, room_id, new_topic).await;
                let _ = promise.send(());
            }
            ClientCommand::GetRooms { promise } => {
                let result = self.get_rooms().await;
                let _ = promise.send(result);
            }
        }
    }

    async fn join_room(&mut self, connection_id: ConnectionId, room_id: RoomId) -> JoinResult {
        if self.banned_from.contains(&room_id) {
            return JoinResult::Banned;
        }

        let room = match self.rooms.get_or_create_room(room_id.clone()).await {
            Ok(room) => room,
            Err(e) => {
                log::error!("Failed to get or create room: {e}");
                todo!();
            }
        };
        room.subscribe(self.player_id.clone(), self.handle.clone()).await;
        self.my_rooms.insert(room_id.clone(), room.clone());
        let room_info = room.get_room_info().await;
        let update = Updates::RoomJoined {
            room_id,
            new_member_id: self.player_id.clone(),
        };
        self.broadcast_update(update, connection_id).await;
        JoinResult::Success(room_info)
    }

    async fn leave_room(&mut self, connection_id: ConnectionId, room_id: RoomId) {
        let room = self.my_rooms.remove(&room_id);
        if let Some(room) = room {
            room.unsubscribe(&self.player_id).await;
        }
        let update = Updates::RoomLeft {
            room_id,
            former_member_id: self.player_id.clone(),
        };
        self.broadcast_update(update, connection_id).await;
    }

    async fn send_message(&mut self, connection_id: ConnectionId, room_id: RoomId, body: Str) {
        let room = self.rooms.get_room(&room_id).await;
        if let Some(room) = room {
            room.send_message(self.player_id.clone(), body.clone()).await;
        } else {
            tracing::info!("no room found");
        }
        let update = Updates::NewMessage {
            room_id,
            author_id: self.player_id.clone(),
            body,
        };
        self.broadcast_update(update, connection_id).await;
    }

    async fn change_topic(&mut self, connection_id: ConnectionId, room_id: RoomId, new_topic: Str) {
        let room = self.rooms.get_room(&room_id).await;
        if let Some(mut room) = room {
            room.set_topic(self.player_id.clone(), new_topic.clone()).await;
        } else {
            tracing::info!("no room found");
        }
        let update = Updates::RoomTopicChanged { room_id, new_topic };
        self.broadcast_update(update, connection_id).await;
    }

    async fn get_rooms(&self) -> Vec<RoomInfo> {
        let mut response = vec![];
        for (_, handle) in &self.my_rooms {
            response.push(handle.get_room_info().await);
        }
        response
    }

    /// Broadcasts an update to all connections except the one with the given id.
    ///
    /// This is called after handling a client command.
    /// Sending the update to the connection which sent the command is handled by the connection itself.
    async fn broadcast_update(&self, update: Updates, except: ConnectionId) {
        for (a, b) in &self.connections {
            if ConnectionId(a) == except {
                continue;
            }
            let _ = b.send(update.clone()).await;
        }
    }
}