use std::error::Error;
use std::net::SocketAddr;
use std::sync::Arc;
use quinn::{Endpoint, ServerConfig};
use rustls::pki_types::{CertificateDer, PrivatePkcs8KeyDer};
use rustls::pki_types::pem::PemObject;

/// 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
pub fn make_server_endpoint(
    bind_addr: SocketAddr,
    cert_file: Option<String>
) -> Result<(Endpoint, CertificateDer<'static>), Box<dyn Error + Send + Sync + 'static>> {
    let (server_config, server_cert) = configure_server(cert_file)?;
    let endpoint = Endpoint::server(server_config, bind_addr)?;
    Ok((endpoint, server_cert))
}

/// Returns default server configuration along with its certificate.
fn configure_server(
    cert_file: Option<String>
) -> Result<(ServerConfig, CertificateDer<'static>), Box<dyn Error + Send + Sync + 'static>> {
    let cert_closure = |cert_file: Option<String>| {
        return if (cert_file.is_some()) {
            let cert = rcgen::generate_simple_self_signed(vec!["localhost".into()]).unwrap();
            let cert_der = CertificateDer::from(cert.cert);
            (cert_der, PrivatePkcs8KeyDer::from(cert.key_pair.serialize_der()))
        } else {
            let mut certs: Vec<_> = CertificateDer::pem_file_iter(cert_file.clone().unwrap())
                .unwrap()
                .collect();
            let cert = certs.pop().unwrap().unwrap();
            (cert, PrivatePkcs8KeyDer::from_pem_file(cert_file.unwrap()).unwrap())
        }
    };
    let (cert_der, priv_key) = cert_closure(cert_file);
    let mut server_config =
        ServerConfig::with_single_cert(vec![cert_der.clone()], priv_key.into())?;
    let transport_config = Arc::get_mut(&mut server_config.transport).unwrap();
    transport_config.max_concurrent_uni_streams(0_u8.into());

    Ok((server_config, cert_der))
}