use socket2::{Domain, Protocol, Socket, Type};
use std::io::{Error, ErrorKind};
use std::mem::MaybeUninit;
use std::net::Ipv4Addr;
use vrrpd::vrrpv2::{self, VRRPv2, VRRPv2Error};

fn main() -> std::io::Result<()> {
    let sock = Socket::new(Domain::IPV4, Type::RAW, Some(Protocol::from(112)))?;
    sock.join_multicast_v4(
        &Ipv4Addr::new(224, 0, 0, 18),
        &Ipv4Addr::UNSPECIFIED,
    )?;
    let vrrp = recv_vrrp(sock).map_err(|err| {
        Error::new(ErrorKind::InvalidData, format!("recv_vrrp(): {err}"))
    })?;
    eprintln!("vrrp: {vrrp:?}");
    Ok(())
}

fn recv_vrrp(sock: Socket) -> Result<VRRPv2, VRRPv2Error> {
    let mut buf = [MaybeUninit::<u8>::uninit(); 512];
    let (nbytes, _) = sock.recv_from(&mut buf)?;
    let bytes = unsafe {
        std::slice::from_raw_parts(buf.as_ptr() as *const u8, nbytes)
    };
    let ttl: u8 = bytes[8];
    if ttl != 255 {
        return Err(VRRPv2Error::InvalidTTL);
    }
    let ihl = bytes[0] & 0xF;
    let data_offset = (ihl * 4) as usize;
    vrrpv2::from_bytes(&bytes[data_offset..])
}