// Copyright 2015-2017 Benjamin Fry <benjaminfry@me.com>
//
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
// http://opensource.org/licenses/MIT>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.

//! System configuration loading
//!
//! This module is responsible for parsing and returning the configuration from
//!  the host system. It will read from the default location on each operating
//!  system, e.g. most Unixes have this written to `/etc/resolv.conf`

use std::fs::File;
use std::io;
use std::io::Read;
use std::net::SocketAddr;
use std::path::Path;
use std::str::FromStr;
use std::time::Duration;

use resolv_conf;

use crate::config::*;
use crate::proto::rr::Name;

const DEFAULT_PORT: u16 = 53;

pub fn read_system_conf() -> io::Result<(ResolverConfig, ResolverOpts)> {
    Ok(read_resolv_conf("/etc/resolv.conf")?)
}

fn read_resolv_conf<P: AsRef<Path>>(path: P) -> io::Result<(ResolverConfig, ResolverOpts)> {
    let mut data = String::new();
    let mut file = File::open(path)?;
    file.read_to_string(&mut data)?;
    parse_resolv_conf(&data)
}

fn parse_resolv_conf<T: AsRef<[u8]>>(data: T) -> io::Result<(ResolverConfig, ResolverOpts)> {
    let parsed_conf = resolv_conf::Config::parse(&data).map_err(|e| {
        io::Error::new(
            io::ErrorKind::Other,
            format!("Error parsing resolv.conf: {:?}", e),
        )
    })?;
    into_resolver_config(parsed_conf)
}

// TODO: use a custom parsing error type maybe?
fn into_resolver_config(
    parsed_config: resolv_conf::Config,
) -> io::Result<(ResolverConfig, ResolverOpts)> {
    let domain = if let Some(domain) = parsed_config.get_system_domain() {
        Some(Name::from_str(domain.as_str())?)
    } else {
        None
    };

    // nameservers
    let mut nameservers = Vec::<NameServerConfig>::with_capacity(parsed_config.nameservers.len());
    for ip in &parsed_config.nameservers {
        nameservers.push(NameServerConfig {
            socket_addr: SocketAddr::new(ip.into(), DEFAULT_PORT),
            protocol: Protocol::Udp,
            tls_dns_name: None,
            #[cfg(feature = "dns-over-rustls")]
            tls_config: None,
        });
        nameservers.push(NameServerConfig {
            socket_addr: SocketAddr::new(ip.into(), DEFAULT_PORT),
            protocol: Protocol::Tcp,
            tls_dns_name: None,
            #[cfg(feature = "dns-over-rustls")]
            tls_config: None,
        });
    }
    if nameservers.is_empty() {
        warn!("no nameservers found in config");
    }

    // search
    let mut search = vec![];
    for search_domain in parsed_config.get_last_search_or_domain() {
        search.push(Name::from_str_relaxed(&search_domain).map_err(|e| {
            io::Error::new(
                io::ErrorKind::Other,
                format!("Error parsing resolv.conf: {:?}", e),
            )
        })?);
    }

    let config = ResolverConfig::from_parts(domain, search, nameservers);

    let mut options = ResolverOpts::default();
    options.ndots = parsed_config.ndots as usize;
    options.timeout = Duration::from_secs(u64::from(parsed_config.timeout));
    options.attempts = parsed_config.attempts as usize;

    Ok((config, options))
}

#[cfg(test)]
mod tests {
    use super::*;
    use proto::rr::Name;
    use std::env;
    use std::net::*;
    use std::str::FromStr;

    fn empty_config() -> ResolverConfig {
        ResolverConfig::from_parts(None, vec![], vec![])
    }

    fn nameserver_config(ip: &str) -> [NameServerConfig; 2] {
        let addr = SocketAddr::new(IpAddr::from_str(ip).unwrap(), 53);
        [
            NameServerConfig {
                socket_addr: addr,
                protocol: Protocol::Udp,
                tls_dns_name: None,
                #[cfg(feature = "dns-over-rustls")]
                tls_config: None,
            },
            NameServerConfig {
                socket_addr: addr,
                protocol: Protocol::Tcp,
                tls_dns_name: None,
                #[cfg(feature = "dns-over-rustls")]
                tls_config: None,
            },
        ]
    }

    fn tests_dir() -> String {
        let server_path = env::var("TDNS_SERVER_SRC_ROOT").unwrap_or_else(|_| ".".to_owned());
        format!("{}/../resolver/tests", server_path)
    }

    #[test]
    #[allow(clippy::redundant_clone)]
    fn test_name_server() {
        let parsed = parse_resolv_conf("nameserver 127.0.0.1").expect("failed");
        let mut cfg = empty_config();
        let nameservers = nameserver_config("127.0.0.1");
        cfg.add_name_server(nameservers[0].clone());
        cfg.add_name_server(nameservers[1].clone());
        assert_eq!(cfg.name_servers(), parsed.0.name_servers());
        assert_eq!(ResolverOpts::default(), parsed.1);
    }

    #[test]
    fn test_search() {
        let parsed = parse_resolv_conf("search localnet.").expect("failed");
        let mut cfg = empty_config();
        cfg.add_search(Name::from_str("localnet.").unwrap());
        assert_eq!(cfg.search(), parsed.0.search());
        assert_eq!(ResolverOpts::default(), parsed.1);
    }

    #[test]
    fn test_underscore_in_search() {
        let parsed = parse_resolv_conf("search Speedport_000").expect("failed");
        let mut cfg = empty_config();
        cfg.add_search(Name::from_str_relaxed("Speedport_000.").unwrap());
        assert_eq!(cfg.search(), parsed.0.search());
        assert_eq!(ResolverOpts::default(), parsed.1);
    }

    #[test]
    fn test_domain() {
        let parsed = parse_resolv_conf("domain example.com").expect("failed");
        let mut cfg = empty_config();
        cfg.set_domain(Name::from_str("example.com").unwrap());
        assert_eq!(cfg, parsed.0);
        assert_eq!(ResolverOpts::default(), parsed.1);
    }

    #[test]
    fn test_read_resolv_conf() {
        read_resolv_conf(format!("{}/resolv.conf-simple", tests_dir())).expect("simple failed");
        read_resolv_conf(format!("{}/resolv.conf-macos", tests_dir())).expect("macos failed");
        read_resolv_conf(format!("{}/resolv.conf-linux", tests_dir())).expect("linux failed");
    }
}