#!/bin/bash -x

##
## Update a Route53 record with this host's IP addresses.
##
## $DIR/.dyndns/config should contain something like:
##   ZONEID="AWS_ZONE_ID"
##   TTL=60
##   ENABLE_IP6=true
##   ENABLE_IP4=false
##
## Adapted from https://willwarren.com/2014/07/03/roll-dynamic-dns-service-using-amazon-route53/
##

DIR=$HOME/.dyndns

if [ ! -f $DIR/config ]; then
    echo "Config is missing. Exiting."
    exit 1
fi

source $DIR/config

RECORDSET=$(hostname --fqdn)
COMMENT="Auto updating @ `date`"

IP4=$(dig +short myip.opendns.com @resolver1.opendns.com)
IP6=$((ip -6 addr list|grep inet6|grep global|grep -v temporary|awk '{print $2}'; ip -6 addr list|grep inet6|grep global|grep temporary|awk '{print $2}')|grep -v '^fd00:'|head -n1|cut -d/ -f1)

function valid_ip4()
{
    local ip=$1
    local stat=1

    if [[ $ip =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]]; then
        OIFS=$IFS
        IFS='.'
        ip=($ip)
        IFS=$OIFS
        [[ ${ip[0]} -le 255 && ${ip[1]} -le 255 \
            && ${ip[2]} -le 255 && ${ip[3]} -le 255 ]]
        stat=$?
    fi
    return $stat
}

function update_dns() {
    local IP=$1
    local TYPE=$2
    local TMPFILE=$(mktemp /tmp/temporary-file.XXXXXXXX)
    cat > ${TMPFILE} << EOF
    {
      "Comment":"$COMMENT",
      "Changes":[
        {
          "Action":"UPSERT",
          "ResourceRecordSet":{
            "ResourceRecords":[
              {
                "Value":"$IP"
              }
            ],
            "Name":"$RECORDSET",
            "Type":"$TYPE",
            "TTL":$TTL
          }
        }
      ]
    }
EOF

    # Update the Hosted Zone record
    aws route53 change-resource-record-sets \
        --hosted-zone-id $ZONEID \
        --change-batch file://"$TMPFILE"
    ret="$?"
    echo

    # Clean up
    rm $TMPFILE

    return $ret
}

IP4FILE="$DIR/ip4"
IP6FILE="$DIR/ip6"

# IPv4
if $ENABLE_IP4 && valid_ip4 $IP4; then
    touch "$IP4FILE"

    if grep -Fxq "$IP4" "$IP4FILE"; then
        echo "IP is still $IP4. Skipping."
    else
        echo "IP4 has changed to $IP4"
        update_dns $IP4 A && echo "$IP4" > "$IP4FILE"
    fi
fi

# IPv6
if $ENABLE_IP6 && [ -n "$IP6" ]; then
    touch "$IP6FILE"

    if grep -Fxq "$IP6" "$IP6FILE"; then
        echo "IP is still $IP6. Skipping."
    else
        echo "IP6 has changed to $IP6"
        update_dns $IP6 AAAA && echo "$IP6" > "$IP6FILE"
    fi
fi