//! Crate for discovering Holochain peers over MDNS
//! Works by broadcasting a service named `HC_SERVICE_NAME`
//! and adding base64 encoded data in a TXT record
//!
//! Uses libmdns crate for broadcasting
//! Uses mdns crate for discovery
use err_derive::Error;
use mdns::RecordKind;
use std::time::Duration;
use tokio_stream::{Stream, StreamExt};

use std::sync::atomic::{AtomicBool, Ordering};

const HC_SERVICE_PROTOCOL: &str = "._udp";
const BROADCAST_INTERVAL_SEC: u64 = 8;
const QUERY_INTERVAL_SEC: u64 = 5;
const MAX_TXT_SIZE: usize = 192;

#[derive(Debug, Error)]
pub enum MdnsError {
    #[error(display = "Regular Mdns error {}", _0)]
    Mdns(#[error(source)] mdns::Error),
    #[error(display = "Base64 decoding error {}", _0)]
    Base64(#[error(source)] base64::DecodeError),
}

/// Stop thread created by `mdns_create_broadcast_thread()`
pub fn mdns_kill_thread(can_run: ::std::sync::Arc<AtomicBool>) {
    can_run.store(false, Ordering::Relaxed);
}

/// Create a thread that will broadcast a holochain service over mdns
/// Returns Sender for sending thread termination command
pub fn mdns_create_broadcast_thread(
    service_type: String,
    service_name: String,
    buffer: &[u8],
) -> ::std::sync::Arc<AtomicBool> {
    let svc_type = format!("_{}{}", service_type, HC_SERVICE_PROTOCOL);
    // Constraints in libmdns
    assert!(
        svc_type.len() < 63,
        "len = {} ({}) ; {}",
        svc_type.len(),
        service_type.len(),
        service_type
    );
    assert!(service_name.len() < 63);
    // Create Termination command variable
    let can_run = ::std::sync::Arc::new(AtomicBool::new(true));
    let can_run_clone = can_run.clone();
    // Change buffer to base64 string
    let mut b64 = format!(
        "u{}",
        base64::encode_config(buffer, base64::URL_SAFE_NO_PAD)
    );
    //println!(
    //    "Broadcasting service type '{}', named '{}' over mdns ({})",
    //    svc_type,
    //    service_name,
    //    b64.len()
    //);
    // Create thread
    let _handle = tokio::task::spawn(async move {
        // Split buffer to fix TXT max size
        let mut substrs = Vec::new();
        while b64.len() > MAX_TXT_SIZE {
            let start: String = b64.drain(..MAX_TXT_SIZE).collect();
            substrs.push(start);
        }
        substrs.push(b64);
        let txts: Vec<_> = substrs.iter().map(AsRef::as_ref).collect();
        //println!("Entering mdns broadcasting thread...");
        // Create mdns responder

        let responder = libmdns::Responder::new().unwrap();
        let _svc = responder.register(svc_type, service_name, 0, &txts);
        // Loop forever unless termination command received
        loop {
            tokio::time::sleep(::std::time::Duration::from_secs(BROADCAST_INTERVAL_SEC)).await;
            if !can_run_clone.load(Ordering::Relaxed) {
                //println!("Terminating.");
                break;
            }
        }
    });
    // Done
    can_run
}

///
#[derive(Debug, Clone)]
pub struct MdnsResponse {
    /// Service type used
    pub service_type: String,
    /// Service name used
    pub service_name: String,
    /// IP address that responded to the mdns query
    pub addr: std::net::IpAddr,
    /// Data contained in the TXT record
    pub buffer: Vec<u8>,
}

/// Queries the network for the holochain service.
/// Returns an iterator over all responses received.
#[allow(clippy::let_and_return)]
pub fn mdns_listen(service_type: String) -> impl Stream<Item = Result<MdnsResponse, MdnsError>> {
    //let service_name = format!("{}.local", HC_SERVICE_TYPE);
    let svc_type = format!("_{}{}.local", service_type, HC_SERVICE_PROTOCOL);
    //println!("MDNS query for service type '{}'", svc_type);
    let query = mdns::discover::all(svc_type, Duration::from_secs(QUERY_INTERVAL_SEC))
        .expect("mdns Discover failed");
    // Get Mdns Response stream
    let response_stream = query.listen();
    // Change it into a MdnsResponse stream
    let mdns_stream = response_stream
        // Filtering out Empty responses
        .filter(move |res| {
            match res {
                Ok(response) => !response.is_empty() && response.ip_addr().is_some(),
                Err(_) => true, // Keep errors
            }
        })
        .map(|maybe_response| {
            if let Err(e) = maybe_response {
                return Err(MdnsError::Mdns(e));
            }
            let response = maybe_response.unwrap();
            // NOTE: if response.ip_addr() is not te right address,
            // we should give all A/AAA records found in the answers instead
            let addr = response.ip_addr().unwrap(); // should have already been filtered out
            let mut buffer = Vec::new();
            let mut service_name = String::new();
            let mut service_type = String::new();
            //println!("Response Answer count = {}", response.answers.len());
            for answer in response.answers {
                match answer.kind {
                    RecordKind::TXT(txts) => {
                        //println!("TXT count = {}", txts.len());
                        let mut b64 = String::new();
                        for txt in txts {
                            //println!("Response TXT = {:?}", txt);
                            b64.push_str(&txt);
                        }
                        buffer = match base64::decode_config(&b64[1..], base64::URL_SAFE_NO_PAD) {
                            Err(e) => return Err(MdnsError::Base64(e)),
                            Ok(s) => s,
                        };
                    }
                    // Retrieve service name stored in PTR record
                    RecordKind::PTR(ptr) => {
                        //println!("PTR = {}", ptr);
                        service_name = ptr
                            .split('.')
                            .next()
                            .expect("Found service without a name")
                            .to_string();
                        let names: Vec<&str> = answer.name.split("._").collect();
                        //println!("answer.name = {}", answer.name);
                        service_type = names[0][1..].to_string();
                    }
                    _ => {}
                }
            }
            Ok(MdnsResponse {
                service_type,
                service_name,
                addr,
                buffer,
            })
        });
    // Done
    mdns_stream
}