use anyhow::anyhow;
use hickory_resolver::config::{NameServerConfig, ResolverConfig, ResolverOpts};
use hickory_resolver::TokioAsyncResolver;
use log::warn;
use std::net::{IpAddr, SocketAddr, SocketAddrV4, SocketAddrV6};
use url::{Host, Url};

#[derive(Clone)]
pub enum DnsResolver {
    System,
    TrustDns(TokioAsyncResolver),
}

impl DnsResolver {
    pub async fn lookup_host(&self, domain: &str, port: u16) -> anyhow::Result<Vec<SocketAddr>> {
        let addrs: Vec<SocketAddr> = match self {
            Self::System => tokio::net::lookup_host(format!("{}:{}", domain, port)).await?.collect(),
            Self::TrustDns(dns_resolver) => dns_resolver
                .lookup_ip(domain)
                .await?
                .into_iter()
                .map(|ip| match ip {
                    IpAddr::V4(ip) => SocketAddr::V4(SocketAddrV4::new(ip, port)),
                    IpAddr::V6(ip) => SocketAddr::V6(SocketAddrV6::new(ip, port, 0, 0)),
                })
                .collect(),
        };

        Ok(addrs)
    }

    pub fn new_from_urls(resolvers: &[Url]) -> anyhow::Result<Self> {
        if resolvers.is_empty() {
            // no dns resolver specified, fall-back to default one
            let Ok((cfg, mut opts)) = hickory_resolver::system_conf::read_system_conf() else {
                warn!("Fall-backing to system dns resolver. You should consider specifying a dns resolver. To avoid performance issue");
                return Ok(Self::System);
            };

            opts.timeout = std::time::Duration::from_secs(1);
            // Windows end-up with too many dns resolvers, which causes a performance issue
            // https://github.com/hickory-dns/hickory-dns/issues/1968
            #[cfg(target_os = "windows")]
            {
                opts.cache_size = 1024;
                opts.num_concurrent_reqs = cfg.name_servers().len();
            }
            return Ok(Self::TrustDns(hickory_resolver::AsyncResolver::tokio(cfg, opts)));
        };

        // if one is specified as system, use the default one from libc
        if resolvers.iter().any(|r| r.scheme() == "system") {
            return Ok(Self::System);
        }

        // otherwise, use the specified resolvers
        let mut cfg = ResolverConfig::new();
        for resolver in resolvers.iter() {
            let (protocol, port) = match resolver.scheme() {
                "dns" => (hickory_resolver::config::Protocol::Udp, resolver.port().unwrap_or(53)),
                "dns+https" => (hickory_resolver::config::Protocol::Https, resolver.port().unwrap_or(443)),
                "dns+tls" => (hickory_resolver::config::Protocol::Tls, resolver.port().unwrap_or(853)),
                _ => return Err(anyhow!("invalid protocol for dns resolver")),
            };
            let host = resolver
                .host()
                .ok_or_else(|| anyhow!("Invalid dns resolver host: {}", resolver))?;
            let sock = match host {
                Host::Domain(host) => match Host::parse(host) {
                    Ok(Host::Ipv4(ip)) => SocketAddr::V4(SocketAddrV4::new(ip, port)),
                    Ok(Host::Ipv6(ip)) => SocketAddr::V6(SocketAddrV6::new(ip, port, 0, 0)),
                    Ok(Host::Domain(_)) | Err(_) => {
                        return Err(anyhow!("Dns resolver must be an ip address, got {}", host));
                    }
                },
                Host::Ipv4(ip) => SocketAddr::V4(SocketAddrV4::new(ip, port)),
                Host::Ipv6(ip) => SocketAddr::V6(SocketAddrV6::new(ip, port, 0, 0)),
            };
            cfg.add_name_server(NameServerConfig::new(sock, protocol))
        }

        let mut opts = ResolverOpts::default();
        opts.timeout = std::time::Duration::from_secs(1);
        Ok(Self::TrustDns(hickory_resolver::AsyncResolver::tokio(cfg, opts)))
    }
}