extern crate rand;
#[macro_use]
extern crate rust_util;

use std::collections::HashMap;
use std::env;
use std::net::UdpSocket;
use std::sync::Arc;
use std::sync::atomic::{ AtomicBool, Ordering };
use std::sync::mpsc::channel;
use std::thread;
use std::time::Duration;
use clap::{ Arg, App };

const LOCAL_ADDR: &str = "127.0.0.1";
const TIMEOUT: u64 = 3 * 60 * 100; //3 minutes

fn main() {
    let matches = App::new("Simple Rust UDP Proxy")
        .version(env!("CARGO_PKG_VERSION"))
        .about(env!("CARGO_PKG_DESCRIPTION"))
        .arg(Arg::with_name("local_port").short("l").long("local-port").takes_value(true).required(true)
            .help("The local port to which udpproxy should bind to"))
        .arg(Arg::with_name("remote_port").short("r").long("remote-port").takes_value(true).required(true)
            .help("The remote port to which UDP packets should be forwarded"))
        .arg(Arg::with_name("host").short("h").long("host").takes_value(true).required(true)
            .help("The remote address to which packets will be forwarded"))
        .arg(Arg::with_name("bind").short("b").long("bind").takes_value(true)
            .help("The address on which to listen for incoming requests"))
        .arg(Arg::with_name("debug").short("d").long("debug").takes_value(true)
            .help("Enable debug mode"))
        .arg(Arg::with_name("allowed_list").short("A").long("allowed-list").takes_value(true).multiple(true).help("Allowed IP list, e.g. 127.0.0.1, 120.0.0.0/8"))
        .get_matches();

    let local_port: u16 = matches.value_of("local_port").unwrap().parse().unwrap();
    let remote_port: u16 = matches.value_of("remote_port").unwrap().parse().unwrap();
    let remote_host = matches.value_of("host").unwrap();
    let bind_addr = match matches.value_of("bind") {
        Some(addr) => addr.to_owned(),
        None => LOCAL_ADDR.to_owned(),
    };

    forward(&bind_addr, local_port, &remote_host, remote_port);
}

fn forward(bind_addr: &str, local_port: u16, remote_host: &str, remote_port: u16) {
    let local_addr = format!("{}:{}", bind_addr, local_port);
    debugging!("Listen address and port: {}", local_addr);
    let local = UdpSocket::bind(&local_addr).unwrap_or_else(|_| panic!("Unable to bind to {}", &local_addr));
    information!("Listening on {}", local.local_addr().unwrap());

    let remote_addr = format!("{}:{}", remote_host, remote_port);

    let responder = local.try_clone().unwrap_or_else(
        |_| panic!("Failed to clone primary listening address socket {}", local.local_addr().unwrap())
    );
    let (main_sender, main_receiver) = channel::<(_, Vec<u8>)>();
    thread::spawn(move || {
        debugging!("Started new thread to deal out responses to clients");
        loop {
            let (dest, buf) = main_receiver.recv().unwrap();
            let to_send = buf.as_slice();
            responder.send_to(to_send, dest).unwrap_or_else(
                |_| panic!("Failed to forward response from upstream server to client {}", dest)
            );
        }
    });

    let mut client_map = HashMap::new();
    let mut buf = [0; 64 * 1024];
    loop {
        let (num_bytes, src_addr) = local.recv_from(&mut buf).expect("Didn't receive data");
        // TODO check src_addr ...

        //we create a new thread for each unique client
        let mut remove_existing = false;
        loop {
            debugging!("Received packet from client {}", src_addr);

            let mut ignore_failure = true;
            let client_id = format!("{}", src_addr);

            if remove_existing {
                debugging!("Removing existing forwarder from map: {}", client_id);
                client_map.remove(&client_id);
            }

            let sender = client_map.entry(client_id.clone()).or_insert_with(|| {
                //we are creating a new listener now, so a failure to send shoud be treated as an error
                ignore_failure = false;

                let local_send_queue = main_sender.clone();
                let (sender, receiver) = channel::<Vec<u8>>();
                let remote_addr_copy = remote_addr.clone();
                thread::spawn(move|| {
                    //regardless of which port we are listening to, we don't know which interface or IP
                    //address the remote server is reachable via, so we bind the outgoing
                    //connection to 0.0.0.0 in all cases.
                    let temp_outgoing_addr = format!("0.0.0.0:{}", 1024 + rand::random::<u16>());
                    debugging!("Establishing new forwarder for client {} on {}", src_addr, &temp_outgoing_addr);
                    let upstream_send = UdpSocket::bind(&temp_outgoing_addr).unwrap_or_else(
                        |_| panic!("Failed to bind to transient address {}", &temp_outgoing_addr)
                    );
                    let upstream_recv = upstream_send.try_clone().unwrap_or_else(
                        |_| panic!("Failed to clone client-specific connection to upstream!")
                    );

                    let mut timeouts: u64 = 0;
                    let timed_out = Arc::new(AtomicBool::new(false));

                    let local_timed_out = timed_out.clone();
                    thread::spawn(move|| {
                        let mut from_upstream = [0; 64 * 1024];
                        upstream_recv.set_read_timeout(Some(Duration::from_millis(TIMEOUT + 100))).unwrap();
                        loop {
                            match upstream_recv.recv_from(&mut from_upstream) {
                                Ok((bytes_rcvd, _)) => {
                                    let to_send = from_upstream[..bytes_rcvd].to_vec();
                                    local_send_queue.send((src_addr, to_send)).expect("Failed to queue response from upstream server for forwarding!");
                                },
                                Err(_) => {
                                    if local_timed_out.load(Ordering::Relaxed) {
                                        debugging!("Terminating forwarder thread for client {} due to timeout", src_addr);
                                        break;
                                    }
                                },
                            };
                        }
                    });

                    loop {
                        match receiver.recv_timeout(Duration::from_millis(TIMEOUT)) {
                            Ok(from_client) =>  {
                                upstream_send.send_to(from_client.as_slice(), &remote_addr_copy).unwrap_or_else(
                                    |_| panic!("Failed to forward packet from client {} to upstream server!", src_addr)
                                );
                                timeouts = 0; //reset timeout count
                            },
                            Err(_) => {
                                timeouts += 1;
                                if timeouts >= 10 {
                                    debugging!("Disconnecting forwarder for client {} due to timeout", src_addr);
                                    timed_out.store(true, Ordering::Relaxed);
                                    break;
                                }
                            },
                        };
                    }
                });
                sender
            });

            let to_send = buf[..num_bytes].to_vec();
            match sender.send(to_send) {
                Ok(_) => break,
                Err(_) => {
                    if !ignore_failure {
                        panic!("Failed to send message to datagram forwarder for client {}", client_id);
                    }
                    //client previously timed out
                    debugging!("New connection received from previously timed-out client {}", client_id);
                    remove_existing = true;
                    continue;
                },
            }
        }
    }
}