use std::sync::{Arc, Mutex};
use tokio::net::UdpSocket;
use tokio::sync::mpsc::{Receiver, Sender};
use tokio::sync::{mpsc, oneshot};

pub struct TestServer {
    messages: Vec<String>,
    on_next_message: Option<Sender<()>>,
}

impl TestServer {
    pub async fn new(address: String) -> Arc<Mutex<Self>> {
        let server = TestServer {
            messages: vec![],
            on_next_message: None,
        };
        let shared = Arc::new(Mutex::new(server));
        let shared_r = shared.clone();

        let (tx, rx) = oneshot::channel();

        tokio::spawn(async move {
            let socket = UdpSocket::bind(address.clone())
                .await
                .expect(&format!("unable to bind to {:?}", address));

            // Signify that we're listening
            tx.send(()).unwrap();

            loop {
                // tokio::select!
                let mut buf = [0; 100];
                let (amt, _) = socket
                    .recv_from(&mut buf)
                    .await
                    .expect("unable to read from socket");

                let on_next_message: Option<Sender<()>>;
                {
                    let mut s = shared_r.lock().expect("unable to get server mutex");
                    s.message_received(
                        String::from_utf8(buf[0..amt].to_vec())
                            .expect("unable to decode buffer to utf8 string"),
                    );
                    on_next_message = s.on_next_message.clone();
                }
                if let Some(p) = on_next_message {
                    p.send(()).await.expect("unable to resolve promise");
                }
            }
        });

        // Wait for server to be listening
        let _ = rx.await;

        shared
    }
}

impl TestServer {
    pub fn message_received(&mut self, message: String) {
        self.messages.push(message);
    }

    pub fn last_metric(&self) -> Option<&String> {
        self.messages.last()
    }

    pub fn next_message_received(&mut self) -> Receiver<()> {
        let (tx, rx) = mpsc::channel::<()>(1);
        self.on_next_message = Some(tx);
        rx
    }
}