#!/bin/sh

ping -qc 1 "${server}" > /dev/null
if [ ${?} != 0 ]; then
  # We are offline
  exit
fi

cache=.update_ip.cache
server=ns1.example.com
zone=dyn.example.com
host=desktop
secret=""

server_ip=$( dig +short ${server} | grep [0-9] | head -1 )
iface=$( ip route get ${server_ip} | grep -Po '(?<=(dev ))(\S+)' )

# TODO trigger not via cron, but using ip monitor in a while/sleep loop:
#ip monitor address dev ${iface} | while read event; do
#    case "$event" in
#    'Deleted default'*)
#        ...
#        ;;
#    'local '*)
#        ...
#        ;;
#    ...)
#        ...
#        ;;
#    ...
#    esac
#done

# This has to be retrieved externally
new_ip4=$( wget -4 -q -O - https://treehouse.org.za/ip )
# If the iface call fails, we will get several interfaces, so pipe through head to get the first (default) interface
new_ip6=$( ip -6 addr show ${iface} scope global | grep -vE '(mngtmpaddr|deprecated)' | grep -oP '(?<=inet6\s)[\da-f:]+' | grep -vE '^fc' | head -1 )

cur_ip4=$( nslookup -type=a ${host}.${zone} | grep -oP '(?<=^Address:\ )\d+(\.\d+){3}$' | head -1 )
cur_ip6=$( nslookup -type=aaaa ${host}.${zone} | grep -oP '(?<=^Address:\ )[\da-f:]+$' | head -1 )

#if [ -z ${new_ip4} ] && [ -z ${new_ip6} ]; then
if [ -z ${new_ip4} ]; then
        exit;
fi

if [ -z ${cache} ]; then
        exit;
fi

if [ -f "${HOME}/${cache}" ]; then
        old_ip4=$( cat "${HOME}/${cache}" | grep "\." )
        old_ip6=$( cat "${HOME}/${cache}" | grep "\:" )
fi

if [ "${cur_ip4}" = "${new_ip4}" ] && [ "${new_ip4}" = "${old_ip4}" ] &&
   [ "${cur_ip6}" = "${new_ip6}" ] && [ "${new_ip6}" = "${old_ip6}" ]; then
        exit;
else
        rm -f "${HOME}/${cache}"
fi

if [ -f "${HOME}/${cache}" ]; then
        old_ip4=$( cat "${HOME}/${cache}" | grep "\." )
        old_ip6=$( cat "${HOME}/${cache}" | grep "\:" )
fi

if [ "${cur_ip4}" = "${new_ip4}" ] && [ "${new_ip4}" = "${old_ip4}" ] &&
   [ "${cur_ip6}" = "${new_ip6}" ] && [ "${new_ip6}" = "${old_ip6}" ]; then
        exit;
else
        rm -f "${HOME}/${cache}"
fi

ipv6_line=""
if [ -n "${new_ip6}" ] && [ "${cur_ip6}" != "${new_ip6}" ]; then
    ipv6_line="update add ${host}.${zone}. 60 AAAA ${new_ip6}"
fi

update=$( cat <<-EOF
        server ${server}.
        zone ${zone}.
        key ${host}.${zone} ${secret}
        update delete ${host}.${zone}.
        update add ${host}.${zone}. 60 A ${new_ip4}
        ${ipv6_line}
        update add ${host}.${zone}. 60 TXT "Updated on $( date )"
        send
EOF
)

if echo "${update}" | nsupdate ; then
    echo "${new_ip4}" >> "${HOME}/${cache}"
    echo "${new_ip6}" >> "${HOME}/${cache}"
else
    echo "Request was:"
    echo "${update}"
fi