#! /bin/bash
function log() {
    echo "$@"
    "$@"
}

bridge="br0"
tap="$1"
net="$(echo "${tap}" | sed -re 's:[^0-9]+::g')"

case "$0" in
    *.ifup.sh)
        action="up"
        ;;
    *.ifdown.sh)
        action="down"
        ;;
esac

if [ "${action}" = "up" ]
then
    log ifconfig "${tap}" "10.0.${net}.1" up netmask 255.255.255.0

    if [ "$(cat /proc/sys/net/ipv4/ip_forward)" != "1" ]
    then
        echo "echo 1 > /proc/sys/net/ipv4/ip_forward"
              echo 1 > /proc/sys/net/ipv4/ip_forward
    fi
fi

iptables -L -v | awk '
  BEGIN {
    n = 0
  }
  /^Chain FORWARD/,/^$/ {
    if (match($0, /^  /)) {
      n ++
      if ($6 == "'$tap'" || $7 == "'$tap'") {
        print n
      }
    }
  }
' | tac | while read num
do
    log iptables -D FORWARD "${num}"
done

iptables -t nat -L -v | awk '
  BEGIN {
    n = 0
  }
  /^Chain POSTROUTING/,/^$/ {
    if (match($0, /^  /)) {
      n ++
      if ($3 == "MASQUERADE" && $7 == "'$bridge'") {
        print n
      }
    }
  }
' | tac | while read num
do
    log iptables -t nat -D POSTROUTING "${num}"
done

if [ "${action}" = "up" ]
then
    log iptables -t nat -A POSTROUTING -o "${bridge}" -j MASQUERADE

    log iptables -I FORWARD 1 -i "${tap}" -j ACCEPT
    log iptables -I FORWARD 1 -o "${tap}" -m state --state RELATED,ESTABLISHED -j ACCEPT
else
    log ifconfig "${tap}" down
fi