//! A chat server that broadcasts a message to all connections.
//!
//! This is a simple line-based server which accepts WebSocket connections,
//! reads lines from those connections, and broadcasts the lines to all other
//! connected clients.
//!
//! You can test this out by running:
//!
//!     cargo run --features="async-std-runtime" --example server 127.0.0.1:12345
//!
//! And then in another window run:
//!
//!     cargo run --features="async-std-runtime" --example client ws://127.0.0.1:12345/
//!
//! You can run the second command in multiple windows and then chat between the
//! two, seeing the messages from the other client as they're received. For all
//! connected clients they'll all join the same room and see everyone else's
//! messages.

use std::{
    collections::HashMap,
    env,
    io::Error as IoError,
    net::SocketAddr,
    sync::{Arc, Mutex},
};

use futures::prelude::*;
use futures::{
    channel::mpsc::{unbounded, UnboundedSender},
    future, pin_mut,
};

use async_std::net::{TcpListener, TcpStream};
use async_std::task;
use tungstenite::protocol::Message;

type Tx = UnboundedSender<Message>;
type PeerMap = Arc<Mutex<HashMap<SocketAddr, Tx>>>;

async fn handle_connection(peer_map: PeerMap, raw_stream: TcpStream, addr: SocketAddr) {
    println!("Incoming TCP connection from: {}", addr);

    let ws_stream = async_tungstenite::accept_async(raw_stream)
        .await
        .expect("Error during the websocket handshake occurred");
    println!("WebSocket connection established: {}", addr);

    // Insert the write part of this peer to the peer map.
    let (tx, rx) = unbounded();
    peer_map.lock().unwrap().insert(addr, tx);

    let (outgoing, incoming) = ws_stream.split();

    let broadcast_incoming = incoming.try_for_each(|msg| {
        println!(
            "Received a message from {}: {}",
            addr,
            msg.to_text().unwrap()
        );
        let peers = peer_map.lock().unwrap();

        // We want to broadcast the message to everyone except ourselves.
        let broadcast_recipients = peers
            .iter()
            .filter(|(peer_addr, _)| peer_addr != &&addr)
            .map(|(_, ws_sink)| ws_sink);

        for recp in broadcast_recipients {
            recp.unbounded_send(msg.clone()).unwrap();
        }

        future::ok(())
    });

    let receive_from_others = rx.map(Ok).forward(outgoing);

    pin_mut!(broadcast_incoming, receive_from_others);
    future::select(broadcast_incoming, receive_from_others).await;

    println!("{} disconnected", &addr);
    peer_map.lock().unwrap().remove(&addr);
}

async fn run() -> Result<(), IoError> {
    let addr = env::args()
        .nth(1)
        .unwrap_or_else(|| "127.0.0.1:8080".to_string());

    let state = PeerMap::new(Mutex::new(HashMap::new()));

    // Create the event loop and TCP listener we'll accept connections on.
    let try_socket = TcpListener::bind(&addr).await;
    let listener = try_socket.expect("Failed to bind");
    println!("Listening on: {}", addr);

    // Let's spawn the handling of each connection in a separate task.
    while let Ok((stream, addr)) = listener.accept().await {
        task::spawn(handle_connection(state.clone(), stream, addr));
    }

    Ok(())
}

fn main() -> Result<(), IoError> {
    task::block_on(run())
}