// Copyright 2018 Parity Technologies (UK) Ltd.
//
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// copy of this software and associated documentation files (the "Software"),
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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//! A basic chat application with logs demonstrating libp2p and the gossipsub protocol
//! combined with mDNS for the discovery of peers to gossip with.
//!
//! Using two terminal windows, start two instances, typing the following in each:
//!
//! ```sh
//! cargo run --example gossipsub-chat --features=full
//! ```
//!
//! Mutual mDNS discovery may take a few seconds. When each peer does discover the other
//! it will print a message like:
//!
//! ```sh
//! mDNS discovered a new peer: {peerId}
//! ```
//!
//! Type a message and hit return: the message is sent and printed in the other terminal.
//! Close with Ctrl-c.
//!
//! You can open more terminal windows and add more peers using the same line above.
//!
//! Once an additional peer is mDNS discovered it can participate in the conversation
//! and all peers will receive messages sent from it.
//!
//! If a participant exits (Control-C or otherwise) the other peers will receive an mDNS expired
//! event and remove the expired peer from the list of known peers.

use async_std::io;
use futures::{prelude::*, select};
use libp2p::gossipsub::MessageId;
use libp2p::gossipsub::{
    Gossipsub, GossipsubEvent, GossipsubMessage, IdentTopic as Topic, MessageAuthenticity,
    ValidationMode,
};
use libp2p::{
    gossipsub, identity, mdns, swarm::NetworkBehaviour, swarm::SwarmEvent, PeerId, Swarm,
};
use std::collections::hash_map::DefaultHasher;
use std::error::Error;
use std::hash::{Hash, Hasher};
use std::time::Duration;

#[async_std::main]
async fn main() -> Result<(), Box<dyn Error>> {
    // Create a random PeerId
    let local_key = identity::Keypair::generate_ed25519();
    let local_peer_id = PeerId::from(local_key.public());
    println!("Local peer id: {local_peer_id}");

    // Set up an encrypted DNS-enabled TCP Transport over the Mplex protocol.
    let transport = libp2p::development_transport(local_key.clone()).await?;

    // We create a custom network behaviour that combines Gossipsub and Mdns.
    #[derive(NetworkBehaviour)]
    struct MyBehaviour {
        gossipsub: Gossipsub,
        mdns: mdns::async_io::Behaviour,
    }

    // To content-address message, we can take the hash of message and use it as an ID.
    let message_id_fn = |message: &GossipsubMessage| {
        let mut s = DefaultHasher::new();
        message.data.hash(&mut s);
        MessageId::from(s.finish().to_string())
    };

    // Set a custom gossipsub configuration
    let gossipsub_config = gossipsub::GossipsubConfigBuilder::default()
        .heartbeat_interval(Duration::from_secs(10)) // This is set to aid debugging by not cluttering the log space
        .validation_mode(ValidationMode::Strict) // This sets the kind of message validation. The default is Strict (enforce message signing)
        .message_id_fn(message_id_fn) // content-address messages. No two messages of the same content will be propagated.
        .build()
        .expect("Valid config");

    // build a gossipsub network behaviour
    let mut gossipsub = Gossipsub::new(MessageAuthenticity::Signed(local_key), gossipsub_config)
        .expect("Correct configuration");

    // Create a Gossipsub topic
    let topic = Topic::new("test-net");

    // subscribes to our topic
    gossipsub.subscribe(&topic)?;

    // Create a Swarm to manage peers and events
    let mut swarm = {
        let mdns = mdns::async_io::Behaviour::new(mdns::Config::default(), local_peer_id)?;
        let behaviour = MyBehaviour { gossipsub, mdns };
        Swarm::with_async_std_executor(transport, behaviour, local_peer_id)
    };

    // Read full lines from stdin
    let mut stdin = io::BufReader::new(io::stdin()).lines().fuse();

    // Listen on all interfaces and whatever port the OS assigns
    swarm.listen_on("/ip4/0.0.0.0/tcp/0".parse()?)?;

    println!("Enter messages via STDIN and they will be sent to connected peers using Gossipsub");

    // Kick it off
    loop {
        select! {
            line = stdin.select_next_some() => {
                if let Err(e) = swarm
                    .behaviour_mut().gossipsub
                    .publish(topic.clone(), line.expect("Stdin not to close").as_bytes()) {
                    println!("Publish error: {e:?}");
                }
            },
            event = swarm.select_next_some() => match event {
                SwarmEvent::Behaviour(MyBehaviourEvent::Mdns(mdns::Event::Discovered(list))) => {
                    for (peer_id, _multiaddr) in list {
                        println!("mDNS discovered a new peer: {peer_id}");
                        swarm.behaviour_mut().gossipsub.add_explicit_peer(&peer_id);
                    }
                },
                SwarmEvent::Behaviour(MyBehaviourEvent::Mdns(mdns::Event::Expired(list))) => {
                    for (peer_id, _multiaddr) in list {
                        println!("mDNS discover peer has expired: {peer_id}");
                        swarm.behaviour_mut().gossipsub.remove_explicit_peer(&peer_id);
                    }
                },
                SwarmEvent::Behaviour(MyBehaviourEvent::Gossipsub(GossipsubEvent::Message {
                    propagation_source: peer_id,
                    message_id: id,
                    message,
                })) => println!(
                        "Got message: '{}' with id: {id} from peer: {peer_id}",
                        String::from_utf8_lossy(&message.data),
                    ),
                _ => {}
            }
        }
    }
}