#!/bin/sh
set -Ceu

case "${1:-}:${2:-}" in
  "bridge:"|"direct:"|"bridge:<lan>"|"direct:<lan>"|"bridge:<router>"|"direct:<router>")
    mode="${1}" ;;
  *) 
    echo "usage: ${0##*/} bridge|direct"
    exit 1 ;;
esac
func="${2:-}"

xtrace=$(set -o | grep --silent 'xtrace .*on' && printf "%s" "-x" || :)
dir="hairpin.reproduce"
me="${0}"
[ -s "${me}" ] || me=$(which "${me}")

[ x"$(id -u)" = x"0" ] ||
  exec sudo "http_proxy=${http_proxy:-}" "${SHELL}" ${xtrace} "${me}" "$@"

ipld() {
  ! ip link show | egrep --silent "^[0-9]+: ${1}: " ||
    ip link delete dev "${1}"
}
cleanup() {
  set +e
  ipld hp-rt0-host
  ipld hp-rt1-host
  ipld hp-lan-host
  ipld hp-bridge
  ipld hp-internet
  rm -rf "${dir}.lan" "${dir}.router"
}

boot() {
  [ -s "${dir}/${me##*/}" ] || {
    rm -rf "${dir}"
    debootstrap --arch=amd64 --verbose --variant=minbase --include=iproute2,iptables,iputils-ping jessie "${dir}"
  }
  cp "${0}" "${dir}"
  chmod a+rx "${dir}/${me##/}"
  rm -rf "${dir}.router" "${dir}.lan"
  cp -al "${dir}" "${dir}.router"
  cp -al "${dir}" "${dir}.lan"
  trap cleanup 0 1 2 15
  ip link add name hp-rt0-host type veth peer name hp-rt0-client
  ip link add name hp-rt1-host type veth peer name hp-rt1-client
  ip link add name hp-lan-host type veth peer name hp-lan-client
  ip link add name hp-bridge type bridge
  ip link set dev hp-rt0-host master hp-bridge
  ip link set dev hp-rt1-host master hp-bridge
  ip link set up hp-rt0-host
  ip link set up hp-rt1-host
  ip link set dev hp-lan-host master hp-bridge
  ip link set up hp-lan-host
  ip addr add dev hp-bridge 10.99.99.98/30
  ip link set up dev hp-bridge
  ip link add name hp-internet type dummy
  ip addr add dev hp-internet 10.99.99.90/30
  ip link set up dev hp-internet
  echo 1 >|/proc/sys/net/ipv4/ip_forward
  [ -z "${xtrace}" ] || ip addr show
  [ -z "${xtrace}" ] || ip route show
  [ -z "${xtrace}" ] || ping -c 1 -n 10.99.99.90
  [ -z "${xtrace}" ] || echo ================================================
  systemd-nspawn \
    --directory="${dir}.router" \
    --network-interface="hp-rt0-client" \
    --network-interface="hp-rt1-client" \
    --quiet \
    sh ${xtrace} /${me##*/} "${mode}" "<router>" &
  sleep 2
  systemd-nspawn \
    --directory="${dir}.lan" \
    --network-interface="hp-lan-client" \
    --quiet \
    sh ${xtrace} /${me##*/} "${mode}" "<lan>"
  wait
}

router() {
  ip link add name br0 type bridge
  case "${mode}" in
    bridge)
      if=br0
      ip link set dev hp-rt0-client master "${if}"
      ;;
    direct)
      if=hp-rt0-client
      ;;
  esac
  ip link set dev hp-rt1-client master br0
  ip link set up dev br0
  ip addr add dev "${if}" 10.99.99.97/30 
  ip addr add dev "${if}" 10.91.91.1/24
  ip link set up dev hp-rt0-client
  ip link set up dev hp-rt1-client
  ip route add dev "${if}" default via 10.99.99.98
  iptables -t nat -A POSTROUTING -s 10.91.91.0/24 -j MASQUERADE
  echo 1 >|/proc/sys/net/ipv4/ip_forward
  [ -z "${xtrace}" ] || ip addr show
  [ -z "${xtrace}" ] || ip route show
  [ -z "${xtrace}" ] || iptables -t nat -L POSTROUTING --numeric --line-numbers
  sleep 6
}

lan() {
  ip addr add dev hp-lan-client 10.91.91.129/24
  ip link set up dev hp-lan-client
  ip route add dev hp-lan-client default via 10.91.91.1
  [ -z "${xtrace}" ] || ip addr show
  [ -z "${xtrace}" ] || ip route show
  ping -c 1 -n 10.99.99.90 || :
}

case "${func}" in
  "")		boot;;
  "<lan>")	lan;;
  "<router>")	router;;
esac