// Copyright (c) 2014, 2015, 2022 Robert Clipsham <robert@octarineparrot.com>
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.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.

extern crate pnet;

use pnet::datalink;
use pnet::packet::ethernet::{EtherTypes, MutableEthernetPacket};
use pnet::packet::ip::IpNextHeaderProtocols;
use pnet::packet::ipv4::{self, MutableIpv4Packet};
use pnet::packet::udp::{self, MutableUdpPacket};
use pnet::packet::MutablePacket;

use std::env;
use std::net::Ipv4Addr;

static IPV4_HEADER_LEN: usize = 20;
static UDP_HEADER_LEN: usize = 8;
static TEST_DATA_LEN: usize = 5;

pub fn build_ipv4_header(packet: &mut [u8]) -> MutableIpv4Packet {
    let mut ip_header = MutableIpv4Packet::new(packet).unwrap();

    let total_len = (IPV4_HEADER_LEN + UDP_HEADER_LEN + TEST_DATA_LEN) as u16;

    ip_header.set_version(4);
    ip_header.set_header_length(5);
    ip_header.set_total_length(total_len);
    ip_header.set_ttl(4);
    ip_header.set_next_level_protocol(IpNextHeaderProtocols::Udp);
    ip_header.set_source(Ipv4Addr::new(127, 0, 0, 1));
    ip_header.set_destination(Ipv4Addr::new(127, 0, 0, 1));

    let checksum = ipv4::checksum(&ip_header.to_immutable());
    ip_header.set_checksum(checksum);

    ip_header
}

pub fn build_udp_header(packet: &mut [u8]) -> MutableUdpPacket {
    let mut udp_header = MutableUdpPacket::new(packet).unwrap();

    udp_header.set_source(1234); // Arbitrary port number
    udp_header.set_destination(1234);
    udp_header.set_length((UDP_HEADER_LEN + TEST_DATA_LEN) as u16);

    udp_header
}

pub fn build_udp4_packet(packet: &mut [u8], msg: &str) {
    let mut ip_header = build_ipv4_header(packet);
    let source = ip_header.get_source();
    let destination = ip_header.get_destination();
    let mut udp_header = build_udp_header(ip_header.payload_mut());

    {
        let data = udp_header.payload_mut();
        let msg = msg.as_bytes();
        data[0] = msg[0];
        data[1] = msg[1];
        data[2] = msg[2];
        data[3] = msg[3];
        data[4] = msg[4];
    }

    let checksum = udp::ipv4_checksum(&udp_header.to_immutable(), &source, &destination);
    udp_header.set_checksum(checksum);
}

fn main() {
    use pnet::datalink::Channel::Ethernet;

    let interface_name = env::args().nth(1).unwrap();
    let destination = (&env::args().nth(2).unwrap()[..]).parse().unwrap();
    // Find the network interface with the provided name
    let interfaces = datalink::interfaces();
    let interface = interfaces
        .iter()
        .filter(|iface| iface.name == interface_name)
        .next()
        .unwrap();

    // Create a channel to send on
    let mut tx = match datalink::channel(interface, Default::default()) {
        Ok(Ethernet(tx, _)) => tx,
        Ok(_) => panic!("rs_sender: unhandled channel type"),
        Err(e) => panic!("rs_sender: unable to create channel: {}", e),
    };

    let mut buffer = [0u8; 64];
    {
        let mut mut_ethernet_header = MutableEthernetPacket::new(&mut buffer[..]).unwrap();
        mut_ethernet_header.set_destination(destination);
        mut_ethernet_header.set_source(interface.mac.unwrap());
        mut_ethernet_header.set_ethertype(EtherTypes::Ipv4);
        build_udp4_packet(mut_ethernet_header.payload_mut(), "rmesg");
    }

    loop {
        tx.send_to(&buffer, None);
    }
}