use hyper::body::Incoming;
use hyper::{Request, Response, StatusCode};
use hyper::service::service_fn;
use hyper_util::rt::TokioIo;
use http_body_util::{BodyExt, Full};
use rustdns_protocol::packet::DnsPacket;
use rustls::ServerConfig;
use std::net::SocketAddr;
use std::sync::Arc;
use tokio::net::TcpListener;
use tokio_rustls::TlsAcceptor;
use tracing::{error, info};

/// Configuration for the HTTPS DoH server.
pub struct HttpsServerConfig {
    pub bind_addr: SocketAddr,
    pub tls_config: Arc<ServerConfig>,
}

/// An HTTPS DNS-over-HTTPS server.
pub struct HttpsServer {
    shutdown: tokio::sync::watch::Sender<bool>,
    local_addr: SocketAddr,
}

impl HttpsServer {
    /// Start the HTTPS DoH server.
    pub async fn start<F, Fut>(
        config: HttpsServerConfig,
        resolver: F,
    ) -> Result<Self, Box<dyn std::error::Error + Send + Sync>>
    where
        F: Fn(DnsPacket) -> Fut + Send + Sync + 'static,
        Fut: std::future::Future<Output = DnsPacket> + Send + 'static,
    {
        let listener = TcpListener::bind(config.bind_addr).await?;
        let local_addr = listener.local_addr()?;
        let (shutdown_tx, shutdown_rx) = tokio::sync::watch::channel(false);

        let tls_acceptor = TlsAcceptor::from(config.tls_config);
        let resolver = Arc::new(resolver);

        info!("HTTPS DoH server listening on {}", local_addr);

        tokio::spawn(async move {
            let mut shutdown_rx = shutdown_rx;

            loop {
                tokio::select! {
                    result = listener.accept() => {
                        match result {
                            Ok((stream, _peer_addr)) => {
                                let acceptor = tls_acceptor.clone();
                                let resolver = resolver.clone();

                                tokio::spawn(async move {
                                    match acceptor.accept(stream).await {
                                        Ok(tls_stream) => {
                                            let io = TokioIo::new(tls_stream);
                                            let resolver = resolver.clone();

                                            let service = service_fn(move |req: Request<Incoming>| {
                                                let resolver = resolver.clone();
                                                async move {
                                                    handle_doh_request(req, resolver).await
                                                }
                                            });

                                            if let Err(e) = hyper::server::conn::http1::Builder::new()
                                                .serve_connection(io, service)
                                                .await
                                            {
                                                error!("HTTPS connection error: {}", e);
                                            }
                                        }
                                        Err(e) => {
                                            error!("TLS accept error: {}", e);
                                        }
                                    }
                                });
                            }
                            Err(e) => {
                                error!("TCP accept error: {}", e);
                            }
                        }
                    }
                    _ = shutdown_rx.changed() => {
                        if *shutdown_rx.borrow() {
                            info!("HTTPS DoH server shutting down");
                            break;
                        }
                    }
                }
            }
        });

        Ok(HttpsServer {
            shutdown: shutdown_tx,
            local_addr,
        })
    }

    /// Stop the HTTPS server.
    pub fn stop(&self) {
        let _ = self.shutdown.send(true);
    }

    /// Get the bound local address.
    pub fn local_addr(&self) -> SocketAddr {
        self.local_addr
    }
}

async fn handle_doh_request<F, Fut>(
    req: Request<Incoming>,
    resolver: Arc<F>,
) -> Result<Response<Full<bytes::Bytes>>, hyper::Error>
where
    F: Fn(DnsPacket) -> Fut + Send + Sync,
    Fut: std::future::Future<Output = DnsPacket> + Send,
{
    if req.method() == hyper::Method::POST && req.uri().path() == "/dns-query" {
        let body = req.collect().await?.to_bytes();

        match DnsPacket::parse(&body) {
            Ok(request) => {
                let response = resolver(request).await;
                let encoded = response.encode();

                Ok(Response::builder()
                    .status(StatusCode::OK)
                    .header("Content-Type", "application/dns-message")
                    .body(Full::new(bytes::Bytes::from(encoded)))
                    .unwrap())
            }
            Err(e) => {
                error!("Failed to parse DoH request: {}", e);
                Ok(Response::builder()
                    .status(StatusCode::BAD_REQUEST)
                    .body(Full::new(bytes::Bytes::from(format!("Invalid DNS message: {}", e))))
                    .unwrap())
            }
        }
    } else {
        Ok(Response::builder()
            .status(StatusCode::NOT_FOUND)
            .body(Full::new(bytes::Bytes::new()))
            .unwrap())
    }
}

/// Create a rustls ServerConfig from PEM-encoded certificate and key.
pub fn create_tls_config(cert_pem: &str, key_pem: &str) -> Result<Arc<ServerConfig>, Box<dyn std::error::Error + Send + Sync>> {
    let certs = rustls_pemfile::certs(&mut cert_pem.as_bytes())
        .collect::<Result<Vec<_>, _>>()?;
    let key = rustls_pemfile::private_key(&mut key_pem.as_bytes())?
        .ok_or("no private key found in PEM data")?;

    let config = ServerConfig::builder()
        .with_no_client_auth()
        .with_single_cert(certs, key)?;

    Ok(Arc::new(config))
}