#!/bin/bash

#
# you need root access to restart a service! Be carefully!
#

# local base path, you can reuse in config
#SCRIPT_DIR=$(dirname $0);
SCRIPT_DIR=/opt/scripts/ipsec;

#
# libraries
#
#source $SCRIPT_DIR/lib/lib.simulation.sh ;
#source $SCRIPT_DIR/lib/lib.logging.sh ;

#
# configuration, in extra config file or local here
#
#source $SCRIPT_DIR/conf/check.dns.conf.sh;

# directory where the stats file are living
STAT_DIR=${SCRIPT_DIR}/stats ;

# dynamic host names separated by space
#WATCHHOSTS="foo.dyn.ip bar.dynamic.net";
WATCHHOSTS="";

# services to restart separated by space, maybe useful: ipsec, ntp, named, my-smooth-backup 
#SERVICES="ipsec ntp";
SERVICES="";

# email addresses separated by space, for debugging or noisy information, leave blank if not needed
# Note: a local MTA is needed 
#RECEIVER="admin@foobar.net user@foo.com";
RECEIVER="";

# internal parameters, do not change
RESTART=0;
MAILTXT="";

# check stats dir
if [ ! -d $STAT_DIR ];
then
	echo $(date "+%F-%H:%M:%S")": stats directory $STAT_DIR created.";
	mkdir -p $STAT_DIR;
fi;

#
# working on hosts
#
if [ ${#WATCHHOSTS} -gt 0 ];
then
	for SRV in $WATCHHOSTS;
	do 
		# checking stats file
		STAT_FILE=${STAT_DIR}/$SRV.dns ;
		
		# resolving host
		RESOLVE=$(host $SRV | grep "has address");

		if [ ${#RESOLVE} -gt 0 ];
		then
			IP=$(echo $RESOLVE | awk '{print $4}') ;
		else
			IP="";
		fi;
		
		if [ ! -f $STAT_FILE ];
		then
			# no stats file -> create
			echo $(date "+%F-%H:%M:%S")": stat file $STAT_FILE created.";
			touch $STAT_DIR;
			
			if [ ${#IP} -gt 0 ];
			then
				# setting current IP as OLD, because we don't have a stats file
				IP_OLD=$IP ;
				echo $(date "+%F-%H:%M:%S")": setting up old IP for HOST: $SRV to ${IP_OLD}, because we have not monitored it before";
			else
				# could not resolve host
				IP_OLD="NEW_STATS_FILE" ;
			fi;
			
			echo $IP_OLD > $STAT_FILE ;
		else
			# found stats file and reading it
			IP_OLD=$(cat $STAT_FILE);
		fi;
		
		if [ ${#IP} -gt 0 ];
		then
			# we were able to resolve the host
			if [ $IP_OLD != $IP ];
			then
				# remember restart of services
				RESTART=1;

				# IP has changed
				echo $(date "+%F-%H:%M:%S")": Host $SRV has changed their IP $IP, restarting services ...";
				
				# enable for logging to syslog
				# logger "Host $SRV has changed their IP $IP, restarting services ...";
				
				# append to maillog
				MAILTXT=${MAILTXT}"Host: ${SRV}, IP change: ${IP_OLD} to ${IP}"$'\n';

				# write new IP to stats
				echo $IP > $STAT_FILE;
				
			else
				# IP has *NOT* changed
				echo $(date "+%F-%H:%M:%S")": Host $SRV has not changed the IP $IP since we saw them before";
				
				# enable if you want unchanged IPs mailed too
				#MAILTXT=${MAILTXT}"Host: ${SRV}, IP *NOT* changed: ${IP_OLD}"$'\n';
			fi;
		else
			# could not resolve IP
			echo $(date "+%F-%H:%M:%S")": Could not resolve HOST $SRV. Maybe DNS or Internet down?";
		fi;
		
	done;
	
	#
	# restarting services
	#
	if [ $RESTART -eq 1 ];
	then
		# we have an IP change detected
		if [ ${#SERVICES} -gt 0 ];
		then
			# services are defined
			for SVC in $SERVICES;
			do
				echo $(date "+%F-%H:%M:%S")": service $SVC restart";
				
				# be carefully with new upstart scripts, check the cron enviroment for proper configuration
				# UPSTART: service $SVC restart;
				/etc/init.d/$SVC restart;
			done;
		else
			# no restart services defined? You want mailing right?
			echo $(date "+%F-%H:%M:%S")": There are no services for restart defined. But you want mailing right?";		
		fi;
		
		# Mailing to admins?
		if [ ${#RECEIVER} -gt 0 ];
		then
			for MAILRECEIVER in $RECEIVER;
			do
				echo $(date "+%F-%H:%M:%S")": mailing updates to: "$MAILRECEIVER;
				echo "current results for dynamic host monitoring: "$'\n'"-----------------------------------------------------------------------"$'\n'${MAILTXT}$'\n\n'"restarted services: $SERVICES" | mail -s "[$(hostname)] IP change detected" $MAILRECEIVER;
			done;
		else
			if [ ${#SERVICES} -eq 0 ];
			then
				echo $(date "+%F-%H:%M:%S")": Look Ma, I have not setup mailing AND service restarts ;) You want logging right?"; 
			fi;
		fi;
		unset MAILRECEIVER;
		
	fi;
else
	#
	# no WATCHHOSTS defined
	#
	echo $(date "+%F-%H:%M:%S")": What should I look for? Please check the config to setup WATCHHOSTS.";
fi;