#!/bin/sh

# save as /usr/local/bin/tdyndns

set -u

# debug?

if [ $# -gt 0 ] ; then
	DOIT="echo "
	set -x
else
	DOIT=""
fi

# functions

die() {
	echo "$1" >&2
	exit 1
}

warn() {
	echo "$1" >&2
}

# variables

USERNAME=sue
PASSWORD=hygCithOrs5
HOSTNAME=$(hostname)
ZONE=dyn.example.com
FQDN=$HOSTNAME.$USERNAME.$ZONE
NS=ns.example.com
URL="http://dyndns.example.com/nic/update?hostname=$FQDN&myip="

if [ -z "$HOSTNAME" ] ; then
	die "No hostname found."
fi

# data

# alternative: -4 icanhazip.com, -6 icanhazip.com or ipv{4,6}.icanhazip.com
NEWIPV4=$(wget -q -O- http://ipv4.wtfismyip.com/text)
NEWIPV6=$(wget -q -O- http://ipv6.wtfismyip.com/text)

if command -v dig >/dev/null ; then
	OLDIPV4=$(dig -t a    +short $FQDN @$NS)
	OLDIPV6=$(dig -t aaaa +short $FQDN @$NS)
fi
OLDIPV4=${OLDIPV4:-""}
OLDIPV6=${OLDIPV6:-""}

# actions

# old ipv4 gone
if [ -n "$OLDIPV4" -a -z "$NEWIPV4" ] ; then
	$DOIT wget -q -O/dev/null --user=$USERNAME --password=$PASSWORD "${URL}${OLDIPV4}&offline=yes"
	logger -t${0##*/} -perr -- "removing $FQDN / $OLDIPV4"
fi

# old ipv6 gone
if [ -n "$OLDIPV6" -a -z "$NEWIPV6" ] ; then
	$DOIT wget -q -O/dev/null --user=$USERNAME --password=$PASSWORD "${URL}${OLDIPV6}&offline=yes"
	logger -t${0##*/} -perr -- "removing $FQDN / $OLDIPV6"
fi

# new ipv4
if [ -n "$NEWIPV4" -a "$NEWIPV4" != "$OLDIPV4" ] ; then
	$DOIT wget -q -O/dev/null --user=$USERNAME --password=$PASSWORD "${URL}${NEWIPV4}"
	logger -t${0##*/} -perr -- "updating $FQDN to $NEWIPV4"
fi

# new ipv6
if [ -n "$NEWIPV6" -a "$NEWIPV6" != "$OLDIPV6" ] ; then
	$DOIT wget -q -O/dev/null --user=$USERNAME --password=$PASSWORD "${URL}${NEWIPV6}"
	logger -t${0##*/} -perr -- "updating $FQDN to $NEWIPV6"
fi