#!/bin/sh

ENABLE=yes
NAME=Ethernet
IPADDRESS=192.168.1.20
CIDRLEN=
NETWORK=192.168.1.0
NETMASK=255.255.255.0
GATEWAY=192.168.1.1
BROADCAST=
DHCP=no
CIDRLEN=24
NETWORK=192.168.1.0

netinfo() {
   local ipaddr=$1 netmask=$2 oifs=${IFS} mask=255
   local ipb1 ipb2 ipb3 ipb4 nmb1 nmb2 nmb3 nmb4
   IFS=.
   set -- ${ipaddr}; ipb1=${1}; ipb2=${2}; ipb3=${3}; ipb4=${4}
   set -- ${netmask}; nmb1=${1}; nmb2=${2}; nmb3=${3}; nmb4=${4}
   IFS=$SaveIFS

   local network bcast
   network=$(($ipb1 & $nmb1)).$(($ipb2 & $nmb2)).$(($ipb3 & $nmb3)).$(($ipb4 & $nmb4))
   bcast=$(($ipb1 | ($mask ^ $nmb1))).$(($ipb2 | ($mask ^ $nmb2))).$(($ipb3 | ($mask ^ $nmb3))).$(($ipb4 | ($mask ^ $nmb4)))

   _RET_NETWORK=${network}
   _RET_BCAST=${bcast}
}

iface="${1:-eth0}"
file=${2:-/etc/network/interfaces}
[ "$file" = "-" ] || exec <"$file"

hash="#"
cur_iface=""
found=0
while read line; do
	line=${line%%${hash}*}
	[ -n "$line" ] || continue
	set -- ${line}
	case $1 in
		auto) [ "$2" = "$iface" ] && ENABLE=yes;;
		iface)
			[ "$2" = "$iface" ] || continue;
			# if its not static, let the default path handle
			[ "$4" = "static" ] || { DHCP=yes; continue; }
			cur_iface=$2
			found=1
			;;
		*)
			[ "$cur_iface" = "$iface" ] || continue;
			case $1 in
				address) IPADDRESS=${2};;
				netmask) NETMASK=${2};;
				gateway) GATEWAY=${2};;
				address) IPADDRESS=${2};;
			esac
			;;
	esac
done 

[ -n "$IPADDRESS" -a -n "$NETMASK" ] && netinfo "$IPADDRESS" "$NETMASK" &&
	BROADCAST=${_RET_BCAST}

cat <<EOF
# this file was written by: $0 $iface $file
# some short experimentation shows that you must define
# ENABLE NAME CIDRLEN NETWORK and DHCP to get working DHCP
ENABLE=$ENABLE
NAME=Ethernet
IPADDRESS=$IPADDRESS
NETMASK=$NETMASK
GATEWAY=$GATEWAY
BROADCAST=$BROADCAST
DHCP=$DHCP
# the following are not set right, but not believed to matter
CIDRLEN=$CIDRLEN;
NETWORK=$NETWORK
EOF