#!/usr/bin/env bash

quiet=false
while getopts 'q' flag; do
    case "$flag" in
        q)
            quiet=true
            ;;
    esac
done
shift "$((OPTIND-1))"

# we need zone and token, we also accept, netmask, and overrides
zone=$1
device=$2
scope=$3

# stop if we do not have the required information
if [ -z "$zone" -o -z "$token" ]; then
    echo '"-q": quiet flag, to suppress "address unchanged" messages'
    echo "Usage: token=<your-authentication-token> [netmask=64] [ipv4=<override>] [ipv6=<override>] $0 your-name.dynv6.net [-q] [device] [scope]"
    exit 1
fi

# we store ip addresses in files, so we only update when there is a change
file4="$HOME/.dynv6.addr4.$zone"
file6="$HOME/.dynv6.addr6.$zone"

# load existing ip addresses, when available
[ -e $file4 ] && old4=`cat $file4`
[ -e $file6 ] && old6=`cat $file6`

# [device] would be something like "eth0" or "wlan0"
if [ -n "$device" ]; then
    device="dev $device"
fi

# [scope] normally "global", but "link" can be useful in select proxy cases (such as wsl)
if [ -n "$scope" ]; then
    scope="scope $scope"
else
    scope="scope global"
fi

# what command should we use to call the API
if [ -e /usr/bin/curl ]; then
    bin="curl -fsS"
elif [ -e /usr/bin/wget ]; then
    bin="wget -O-"
else
    echo "neither curl nor wget found"
    exit 1
fi

# what command should we use to determine IPv4
if [ -e /usr/bin/dig ]; then
    lookup4="dig -4 +short A myip.opendns.com @resolver1.opendns.com"
else
    lookup4="$bin https://ipinfo.io/ip"
fi

# lookup IPv4, will be skipped if variable already set
if [ -z "$ipv4" ]; then
    ipv4=`$lookup4`
    if [ -z "$ipv4" ]; then
        echo "failed to lookup IPv4 address, continuing with 'auto'"
        ipv4="auto"
    fi
fi

if [ -z "$netmask" ]; then
    netmask="128"
fi

# lookup IPv6, will be skipped if variable already set
if [ -z "$ipv6" ]; then
    ipv6=$(ip -6 addr list $scope $device | grep -v " fd" | sed -n 's/.*inet6 \([0-9a-f:]\+\).*/\1/p' | head -n 1)
    if [ -z "$ipv6" ]; then
        echo "no IPv6 address found"
        exit 1
    fi
fi
ipv6="$ipv6/$netmask"

# update IPv4, if changed
if [ "$old4" = "$ipv4" ]; then
    if [ "$quiet" = false ]; then
        echo "IPv4 address unchanged"
    fi
else
    # send IPv4 address to dynv6
    echo -n "Updating IPv4: "
    $bin "https://dynv6.com/api/update?zone=$zone&ipv4=$ipv4&token=$token"
    echo ""

    # save current IPv4 address
    echo $ipv4 > $file4
fi

# update IPv6, if changed
if [ "$old6" = "$ipv6" ]; then
    if [ "$quiet" = false ]; then
        echo "IPv6 address unchanged"
    fi
else
    # send IPv6 address to dynv6
    echo -n "Updating IPv6: "
    $bin "https://dynv6.com/api/update?zone=$zone&ipv6=$ipv6&token=$token"
    echo ""

    # save current IPv6 address
    echo $ipv6 > $file6
fi