#!/usr/bin/env bash

#rdns.sh - script for dealing with rDNS.

#TODO
#Add more _BIN variables to decrease reliance on $PATH
#IPv6 support
#Finish domain validation function
#RDNS_QUERY_SERVER round-robin?

#variables
PROVIDERNAME=""
DEFAULT_RDNS="hosted-by.$PROVIDERNAME."
ZONE_LOCATION="/var/named/"
ZONE_TAIL="in-addr.arpa"
ZONE_FTAIL=".db"
SYNC_SCRIPT="/scripts/dnscluster synczone"
RDNS_QUERY_SERVER="8.8.4.4"
DIG_BIN="$(command -v dig)"
if [ $? -ne 0 -o -z "$DIG_BIN" ]; then
	echo "Failed to locate 'dig'."
	exit 1
fi

#functions
function usage () {
	# Usage function. Obvious.
	echo "$0 - Usage
$0 ip.address                  : Show current rDNS for the given IP address.
$0 ip.address dns.address      : Set given IP address's rDNS to the given DNS address.
$0 -v ip.address dns.address   : Set given IP's rDNS, and verify it after syncing.
$0 -nv ip.address dns.address  : Set given IP's rDNS without checking forward DNS first.
$0 -r ip.address               : Reset given IP's rDNS to the default ($DEFAULT_RDNS).
$0 -rS ip.address              : Reset given IP's rDNS as -r does, but don't sync to DNS cluster.
$0 -R ip.address               : Remove the given IP's rDNS entry altogether.
$0 -S ip.address               : Sync the authoritative zone for the given IP address to the DNS cluster.
$0 [-h|--help]                 : Show this help text."
}

function validateIP () {
	#validateIP - validates a given IP to ensure it isn't invalid.
	local IP=$1
	local stat=1
	#Regex to do basic IP validation.
	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
		if [[ ${ip[0]} -le 255 && ${ip[1]} -le 255 && ${ip[2]} -le 255 && ${ip[3]} -le 255 ]]; then
			stat=0
		else
			stat=1
		fi
	fi
	return $stat
}

function convertIPToDNSZone () {
	#Converts a given IP to an in-addr.arpa zone (ie, convertIPToDNSZone 192.210.132.5 would return "132.210.192.in-addr.arpa."
	OIFS=$IFS
	set `IFS=".";echo $1`
	IFS=$OIFS
	echo $3.$2.$1.$ZONE_TAIL
}

function getLastOctet () {
	#Gets the last octet of an IP. Since all our IP ranges are /24s, this is okay.
	OIFS=$IFS
	set `IFS=".";echo $1`
	IFS=$OIFS
	echo $4
}

function validateDomain () {
	#Validate a given domain to ensure it's a real domain.
	#This will be implemented later. For now, just please make sure the PTR value is valid.
	return 0
}

function setRDNS () {
	#Modify the rDNS record for the given IP.
	TARGET_IP=$1
	NEW_PTR=$2
	ZONEFILE=$(convertIPToDNSZone $TARGET_IP)
	RECORD=$(getLastOctet $TARGET_IP)
	if [ ! -w "$ZONE_LOCATION$ZONEFILE$ZONE_FTAIL" ]; then
		echo "Failed to locate: $ZONE_LOCATION$ZONEFILE$ZONE_FTAIL"
		return 1
	fi
	CUR_REC=$(getRDNS $TARGET_IP)
	if [ $? -ne 0 ]; then
		#we create the record
		APPENDREC="$RECORD     14400   IN      PTR     $DEFAULT_RDNS"
		#This is disabled for now. We warn, but do not touch.
		echo "$APPENDREC" >> $ZONE_LOCATION$ZONEFILE$ZONE_FTAIL
		echo "Warning: Record for $TARGET_IP did not exist, new record has been created."
		CUR_REC=$(getRDNS $TARGET_IP)
	fi
	#I would use sed for this, but for some reason I can't get match groups to work in sed.
	perl -pi.bak -e "s/^($RECORD\s+.*)\s$CUR_REC/\1\t$NEW_PTR/" $ZONE_LOCATION$ZONEFILE$ZONE_FTAIL
	return 0
}

function getRDNS () {
	#Retrieve the current rDNS record (if any) for the given IP
	ZONEFILE=$(convertIPToDNSZone $1)
	RECORD=$(getLastOctet $1)
	if [ ! -w "$ZONE_LOCATION$ZONEFILE$ZONE_FTAIL" ]; then
		echo "Failed to locate: $ZONE_LOCATION$ZONEFILE$ZONE_FTAIL"
		return 1
	fi
	ZRECORD=$(egrep "^$RECORD\s.*PTR" $ZONE_LOCATION$ZONEFILE$ZONE_FTAIL)
	if [ $? -ne 0 ]; then
		echo "ZONEFILE: $ZONEFILE$ZONE_FTAIL ; LAST OCTET: $RECORD"
		return 1
	fi
	echo $ZRECORD|perl -pe 's/^.*PTR\s+//'
	return 0
}

function removeRDNS () {
        TARGET_IP=$1
        ZONEFILE=$(convertIPToDNSZone $TARGET_IP)
        RECORD=$(getLastOctet $TARGET_IP)
	CUR_PTR="$(getRDNS $TARGET_IP)"
	if [ $? -ne 0 ]; then
		echo "rDNS entry doesn't exist for $TARGET_IP!"
		return 1
	fi
        perl -pi.bak -e "s/^($RECORD\s+.*\n)//" $ZONE_LOCATION$ZONEFILE$ZONE_FTAIL
}

function verifyRDNS () {
	#Check that the rDNS was actually set, using 'host'.
	HOSTOUT=$($DIG_BIN @$RDNS_QUERY_SERVER +short -x $1|sed 's/^[\s ]+//'|sed 's/[\s ]+$//')
	if [ "$HOSTOUT" != "$2" ]; then
		echo $HOSTOUT
		return 1
	fi
	return 0
}

function checkForwardDNS () {
	#Verify that forward DNS is set properly, using 'dig'. This specifically requests an A record, we won't need to worry about AAAA records for a while.
	DIGOUT="$($DIG_BIN @$RDNS_QUERY_SERVER +short $1 A)"
	if [ "$DIGOUT" != "$2" ]; then
		return 1
	fi
	return 0
}

#main script
MODE=""
GOPTS=""
IPADDR=""
DESTDNS=""
ZONE_FILE=""
DO_SYNC=0

#Get options and arguments. I do this old school because I'm too lazy to l2getopts
if [ "$1" == "-h" -o "$1" == "-r" -o "$1" == "-v" -o "$1" == "-R" -o "$1" == "-nv" -o "$1" == "-rS" -o "$1" == "-S" ]; then
	GOPTS="$1"
	IPADDR="$2"
	DESTDNS="$3"
else
	IPADDR="$1"
	DESTDNS="$2"
fi
#First, we ensure that DESTDNS ends with a period.
#We make sure the new PTR value ends with a period.
if [ ! -z "$DESTDNS" ]; then
	TAILREC="$(echo $DESTDNS|tail -c2)"
	if [ "$TAILREC" != "." ]; then
		DESTDNS="$DESTDNS."
	fi
fi
#First we get usage out of the way. Usage is shown if there are no options, or if the only option given is -h, or if $IPADDR is empty.
if [ -z "$IPADDR" -o "$GOPTS" == "-h" ]; then
	usage
	exit
fi

#Then we validate input. $IPADDR should -always- be an IP address, and $DESTDNS should always be a valid DNS address that exists.
validateIP $IPADDR
if [ $? -ne 0 ]; then
	echo "Error: IP address given ($IPADDR) was not valid."
	usage
	exit 1
fi
#Now we can be sure the IP address given exists. Get our "mode" and then start working.
case $GOPTS in
	-r)
		MODE="RESET"
		;;
	-rS)
		MODE="RESETNOSYNC"
		;;
	-R)
		MODE="REMOVE"
		;;
	-S)
		MODE="NOOP"
		DO_SYNC="1"
		;;
	-v)	MODE="SETANDVALIDATE"
		;;
	*)
		if [ ! -z "$DESTDNS" ]; then
			MODE="SET"
		elif [ ! -z "$IPADDR" ]; then
			MODE="GET"
		fi
		;;
esac
if [ "$MODE" == "SET" -a "$GOPTS" == "-nv" ]; then
	MODE="SETNOVERIFY"
fi
#We do the work.
case $MODE in
	RESET)
		setRDNS $IPADDR $DEFAULT_RDNS
		if [ $? -ne 0 ]; then
			echo "Failed to set rDNS!"
			exit 1
		fi
		echo "rDNS set!"
		DO_SYNC=1
		;;
	RESETNOSYNC)
		setRDNS $IPADDR $DEFAULT_RDNS
		if [ $? -ne 0 ]; then
			echo "Failed to set rDNS!"
			exit 1
		fi
		echo "rDNS set!"
		;;
	GET)
		RDNS=$(getRDNS $IPADDR)
		if [ $? -ne 0 ]; then
			echo "Failed to get rDNS for '$IPADDR'! Message: $RDNS"
			exit 1
		fi
		echo "rDNS for '$IPADDR': $RDNS"
		;;
	SET)
		checkForwardDNS $DESTDNS $IPADDR
		if [ $? -ne 0 ]; then
			echo "Forward DNS does not match requested reverse!"
			exit 1
		fi
		setRDNS $IPADDR $DESTDNS
		if [ $? -ne 0 ]; then
			echo "Failed to set rDNS!"
			exit 1
		fi
		echo "rDNS set!"
		DO_SYNC=1
		;;
	SETNOVERIFY)
		checkForwardDNS $DESTDNS $IPADDR
		if [ $? -ne 0 ]; then
			echo "Warning: Forward DNS does not match requested reverse! Continuing anyway.."
		fi
		setRDNS $IPADDR $DESTDNS
		if [ $? -ne 0 ]; then
			echo "Failed to set rDNS!"
			exit 1
		fi
		echo "rDNS set!"
		DO_SYNC=1
		;;
	SETANDVALIDATE)
		checkForwardDNS $DESTDNS $IPADDR
		if [ $? -ne 0 ]; then
			echo "Forward DNS does not match requested reverse!"
			exit 1
		fi
		setRDNS $IPADDR $DESTDNS
		if [ $? -ne 0 ]; then
			echo "Failed to set rDNS!"
			exit 1
		fi
		echo "rDNS set!"
		DO_SYNC=1
		;;
	REMOVE)
		removeRDNS $IPADDR
		if [ $? -ne 0 ]; then
			echo "Failed to remove rDNS record!"
			exit 1
		fi
		echo "rDNS record removed!"
		DO_SYNC=1
		;;
	NOOP)
		;;
	*)
		echo "Clearly, you used this script incorrectly."
		usage
		exit 1
		;;
esac

if [ $DO_SYNC -eq 1 ]; then
	$SYNC_SCRIPT $(convertIPToDNSZone $IPADDR)
	if [ $? -ne 0 ]; then
		echo "Sync failed!"
	fi
	if [ "$MODE" == "SETANDVALIDATE" ]; then
		sleep 5
		FORWARDDNS=$(verifyRDNS $IPADDR $DESTDNS)
		if [ $? -ne 0 ]; then
			echo "Current rDNS for $IPADDR ($FORWARDDNS) does not match '$DESTDNS'!"
		else
			echo "rDNS was properly synchronised and is set to '$DESTDNS'."
		fi
	fi
fi