// I'm not sure where I got this module from, but it's probably from the
// quinn examples, so the license should be okay.

use std::{
	net::SocketAddr,
	sync::Arc,
	time::Duration,
};

use quinn::{
	ClientConfig, Endpoint,
	ServerConfig,
};

/// Constructs a QUIC endpoint configured for use a client only.
///
/// ## Args
///
/// - server_certs: list of trusted certificates.
#[allow(unused)]
pub fn make_client_endpoint(
	bind_addr: SocketAddr,
	server_certs: &[&[u8]],
) -> anyhow::Result<Endpoint> {
	let mut client_cfg = configure_client (server_certs)?;
	let mut transport = quinn::TransportConfig::default ();
	transport.keep_alive_interval (Some (Duration::from_millis (5_000)));
	
	client_cfg.transport_config (Arc::new (transport));
	
	let mut endpoint = Endpoint::client (bind_addr)?;
	endpoint.set_default_client_config (client_cfg);
	Ok(endpoint)
}

/// Constructs a QUIC endpoint configured to listen for incoming connections
/// on a certain address and port.
///
/// ## Returns
///
/// - a stream of incoming QUIC connections
/// - server certificate serialized into DER format
#[allow(unused)]
pub fn make_server_endpoint(bind_addr: SocketAddr) -> anyhow::Result<(Endpoint, Vec<u8>)> {
	let (server_config, server_cert) = configure_server()?;
	let endpoint = Endpoint::server (server_config, bind_addr)?;
	Ok((endpoint, server_cert))
}

/// Builds default quinn client config and trusts given certificates.
///
/// ## Args
///
/// - server_certs: a list of trusted certificates in DER format.
fn configure_client (server_certs: &[&[u8]]) -> anyhow::Result<ClientConfig> {
	let mut certs = rustls::RootCertStore::empty ();
	for cert in server_certs {
		certs.add (&rustls::Certificate (cert.to_vec ()))?;
	}
	
	Ok (ClientConfig::with_root_certificates (certs))
}

/// Returns default server configuration along with its certificate.
#[allow(clippy::field_reassign_with_default)] // https://github.com/rust-lang/rust-clippy/issues/6527
fn configure_server () -> anyhow::Result<(ServerConfig, Vec<u8>)> {
	let cert = rcgen::generate_simple_self_signed(vec!["localhost".into()]).unwrap();
	let cert_der = cert.serialize_der().unwrap();
	let priv_key = cert.serialize_private_key_der();
	let priv_key = rustls::PrivateKey (priv_key);
	let cert_chain = vec! [rustls::Certificate (cert_der.clone ())];
	
	let mut server_config = ServerConfig::with_single_cert (cert_chain, priv_key)?;
	Arc::get_mut (&mut server_config.transport)
	.unwrap ()
	.max_concurrent_uni_streams (0_u8.into ());
	
	Ok ((server_config, cert_der))
}