use std::collections::HashSet;
use std::sync::Arc;

use async_trait::async_trait;
use dashmap::DashMap;
use tokio::sync::mpsc;

use crate::socket::adapter::{Adapter, AdapterError, BroadcastOptions, BusMessage, SocketInfo};
use crate::socket::message_bus::MessageBus;
use crate::socket::packet::Packet;
use crate::socket::parser;
use crate::socket::socket::Socket;

/// Handle incoming bus messages from other servers.
/// Only performs local dispatch — no remote state writes needed.
async fn handle_bus_message(
    msg: BusMessage,
    on_local_broadcast: &Arc<dyn Fn(&Packet, &BroadcastOptions) + Send + Sync + 'static>,
    server_id: &str,
) {
    match msg {
        BusMessage::Broadcast { namespace: _, packet, opts, server_id: sender_id } => {
            if sender_id == server_id {
                return;
            }
            if let Ok(decoded_packet) = parser::decode(&packet) {
                on_local_broadcast(&decoded_packet, &opts);
            }
        }
        // NATS adapter manages room state locally; cross-server join/leave/disconnect
        // are informational only and don't require duplicate state writes.
        BusMessage::SocketJoin { server_id: sender_id, .. }
        | BusMessage::SocketLeave { server_id: sender_id, .. }
        | BusMessage::SocketDisconnect { server_id: sender_id, .. } => {
            if sender_id == server_id {
                return;
            }
        }
    }
}

/// NATS-based adapter that manages room state locally and uses NATS
/// for cross-server broadcast only. Does NOT depend on Redis.
pub struct NatsAdapter {
    message_bus: Arc<dyn MessageBus>,
    room_subscribers: DashMap<String, mpsc::Receiver<Vec<u8>>>,
    socket_rooms: DashMap<String, HashSet<String>>,
    rooms: DashMap<String, HashSet<String>>,
    /// socket_sid → engine_sid mapping for local delivery
    socket_sids: DashMap<String, String>,
    sockets: DashMap<String, Arc<Socket>>,
    server_id: String,
    namespace: String,
    on_local_broadcast: Arc<dyn Fn(&Packet, &BroadcastOptions) + Send + Sync + 'static>,
}

impl NatsAdapter {
    pub fn new(
        message_bus: Arc<dyn MessageBus>,
        server_id: String,
        namespace: String,
        on_local_broadcast: Arc<dyn Fn(&Packet, &BroadcastOptions) + Send + Sync + 'static>,
    ) -> Self {
        Self {
            message_bus,
            server_id,
            namespace,
            on_local_broadcast,
            room_subscribers: DashMap::new(),
            socket_rooms: DashMap::new(),
            rooms: DashMap::new(),
            socket_sids: DashMap::new(),
            sockets: DashMap::new(),
        }
    }

    pub async fn init(&self) -> Result<(), AdapterError> {
        let channels = ["broadcast", "join", "leave", "disconnect"];
        let prefix = format!("socket.io:{}:", self.namespace);

        for channel_type in channels {
            let subject = format!("{}{}", prefix, channel_type);
            match self.message_bus.subscribe(&subject).await {
                Ok(rx) => {
                    self.room_subscribers.insert(channel_type.to_string(), rx);
                }
                Err(e) => return Err(AdapterError::MessageBus(e.to_string())),
            }
        }

        self.spawn_listener();
        Ok(())
    }

    fn spawn_listener(&self) {
        let server_id = self.server_id.clone();
        let on_local_broadcast = self.on_local_broadcast.clone();

        let mut broadcast_rx = self.room_subscribers.remove("broadcast").map(|(_, rx)| rx);
        let mut join_rx = self.room_subscribers.remove("join").map(|(_, rx)| rx);
        let mut leave_rx = self.room_subscribers.remove("leave").map(|(_, rx)| rx);
        let mut disconnect_rx = self.room_subscribers.remove("disconnect").map(|(_, rx)| rx);

        tokio::spawn(async move {
            loop {
                tokio::select! {
                    Some(data) = async { broadcast_rx.as_mut()?.recv().await } => {
                        if let Ok(msg) = serde_json::from_slice::<BusMessage>(&data) {
                            handle_bus_message(msg, &on_local_broadcast, &server_id).await;
                        }
                    }
                    Some(data) = async { join_rx.as_mut()?.recv().await } => {
                        if let Ok(msg) = serde_json::from_slice::<BusMessage>(&data) {
                            handle_bus_message(msg, &on_local_broadcast, &server_id).await;
                        }
                    }
                    Some(data) = async { leave_rx.as_mut()?.recv().await } => {
                        if let Ok(msg) = serde_json::from_slice::<BusMessage>(&data) {
                            handle_bus_message(msg, &on_local_broadcast, &server_id).await;
                        }
                    }
                    Some(data) = async { disconnect_rx.as_mut()?.recv().await } => {
                        if let Ok(msg) = serde_json::from_slice::<BusMessage>(&data) {
                            handle_bus_message(msg, &on_local_broadcast, &server_id).await;
                        }
                    }
                    else => break,
                }
            }
        });
    }
}

#[async_trait]
impl Adapter for NatsAdapter {
    async fn broadcast(&self, packet: &Packet, opts: &BroadcastOptions) -> Result<(), AdapterError> {
        if opts.flags.local_only {
            (self.on_local_broadcast)(packet, opts);
            return Ok(());
        }

        let msg = BusMessage::Broadcast {
            namespace: self.namespace.clone(),
            packet: parser::encode(packet),
            opts: opts.clone(),
            server_id: self.server_id.clone(),
        };

        let payload = serde_json::to_vec(&msg)
            .map_err(|e| AdapterError::Serialization(e.to_string()))?;

        self.message_bus
            .publish(&format!("socket.io:{}:broadcast", self.namespace), &payload)
            .await
            .map_err(|e| AdapterError::MessageBus(e.to_string()))?;

        (self.on_local_broadcast)(packet, opts);
        Ok(())
    }

    async fn register(&self, socket_sid: &str, engine_sid: &str, _ns: &str) -> Result<(), AdapterError> {
        self.socket_sids.insert(socket_sid.to_string(), engine_sid.to_string());
        Ok(())
    }

    async fn add(&self, sid: &str, room: &str, _ns: &str) -> Result<(), AdapterError> {
        self.socket_rooms
            .entry(sid.to_string())
            .and_modify(|set| { set.insert(room.to_string()); })
            .or_insert_with(|| HashSet::from([room.to_string()]));

        self.rooms
            .entry(room.to_string())
            .and_modify(|set| { set.insert(sid.to_string()); })
            .or_insert_with(|| HashSet::from([sid.to_string()]));

        let msg = BusMessage::SocketJoin {
            namespace: self.namespace.clone(),
            sid: sid.to_string(),
            room: room.to_string(),
            server_id: self.server_id.clone(),
        };

        let payload = serde_json::to_vec(&msg)
            .map_err(|e| AdapterError::Serialization(e.to_string()))?;

        self.message_bus
            .publish(&format!("socket.io:{}:join", self.namespace), &payload)
            .await
            .map_err(|e| AdapterError::MessageBus(e.to_string()))?;

        Ok(())
    }

    async fn del(&self, sid: &str, room: &str, _ns: &str) -> Result<(), AdapterError> {
        if let Some(mut entry) = self.socket_rooms.get_mut(sid) {
            entry.value_mut().remove(room);
        }
        if self.socket_rooms.get(sid).map(|e| e.value().is_empty()).unwrap_or(true) {
            self.socket_rooms.remove(sid);
        }

        if let Some(mut entry) = self.rooms.get_mut(room) {
            entry.value_mut().remove(sid);
        }
        if self.rooms.get(room).map(|e| e.value().is_empty()).unwrap_or(true) {
            self.rooms.remove(room);
        }

        let msg = BusMessage::SocketLeave {
            namespace: self.namespace.clone(),
            sid: sid.to_string(),
            room: room.to_string(),
            server_id: self.server_id.clone(),
        };

        let payload = serde_json::to_vec(&msg)
            .map_err(|e| AdapterError::Serialization(e.to_string()))?;

        self.message_bus
            .publish(&format!("socket.io:{}:leave", self.namespace), &payload)
            .await
            .map_err(|e| AdapterError::MessageBus(e.to_string()))?;

        Ok(())
    }

    async fn del_all(&self, sid: &str, _ns: &str) -> Result<(), AdapterError> {
        if let Some((_, rooms)) = self.socket_rooms.remove(sid) {
            for room in &rooms {
                if let Some(mut entry) = self.rooms.get_mut(room) {
                    entry.value_mut().remove(sid);
                }
                if self.rooms.get(room).map(|e| e.value().is_empty()).unwrap_or(true) {
                    self.rooms.remove(room);
                }
            }
        }

        self.socket_sids.remove(sid);
        self.sockets.remove(sid);

        let msg = BusMessage::SocketDisconnect {
            namespace: self.namespace.clone(),
            sid: sid.to_string(),
            server_id: self.server_id.clone(),
        };

        let payload = serde_json::to_vec(&msg)
            .map_err(|e| AdapterError::Serialization(e.to_string()))?;

        self.message_bus
            .publish(&format!("socket.io:{}:disconnect", self.namespace), &payload)
            .await
            .map_err(|e| AdapterError::MessageBus(e.to_string()))?;

        Ok(())
    }

    async fn fetch_sockets(&self, opts: &BroadcastOptions) -> Result<Vec<SocketInfo>, AdapterError> {
        let mut result = Vec::new();

        let target_sids: HashSet<String> = if opts.rooms.is_empty() {
            self.socket_sids.iter().map(|e| e.key().clone()).collect()
        } else {
            let mut sids = HashSet::new();
            for room in &opts.rooms {
                if let Some(entry) = self.rooms.get(room) {
                    sids.extend(entry.value().iter().cloned());
                }
            }
            sids
        };

        for sid in target_sids {
            if opts.except.contains(&sid) {
                continue;
            }
            let rooms = self.socket_rooms.get(&sid).map(|e| e.value().clone()).unwrap_or_default();
            result.push(SocketInfo {
                sid: sid.clone(),
                namespace: self.namespace.clone(),
                rooms,
            });
        }

        Ok(result)
    }

    async fn socket_rooms(&self, sid: &str) -> Result<HashSet<String>, AdapterError> {
        Ok(self.socket_rooms.get(sid).map(|e| e.value().clone()).unwrap_or_default())
    }

    fn server_id(&self) -> &str {
        &self.server_id
    }

    async fn close(&self) -> Result<(), AdapterError> {
        self.message_bus.close().await.map_err(|e| AdapterError::MessageBus(e.to_string()))?;
        Ok(())
    }
}