#!/bin/sh /etc/rc.common

# make sure this script is started AFTER the start of dnsmasq
START=66
# make sure this script is stopped AFTER the shutdown of the network
STOP=91

# source the configuration
source "/etc/inithost.cfg"

###
### Functions                                                                                                
###

### unpack_hostfile
# unpacks an persistent, compressed host file thus
# preparing it for usage as an dnsmasq host file
# 1. filters out the whitelisted items
# 2. sorts it and removes duplicates
# 3. adds the redirection IP
unpack_hostfile() {
        zcat $1 | filter_whitelist
}

### is_hostfile_consistent
# this function checks whether the persistent host file under
# $PERSISTENTDIR and its corresponding compressed gz file
# contain consistent context or not
is_hostfile_consistent() {
        local CHKSUM1=$( unpack_hostfile "$PERSISTENTDIR/$1.gz" | md5sum | awk '{print $1}' )
        local CHKSUM2=$( md5sum "$PERSISTENTDIR/$1" | awk '{print $1}' )
        test $CHKSUM1 = $CHKSUM2
}

### restore_persistent_hostfiles
# this function is used prior to any internet accessability
# and will install any persistently saved host files
# this will circumvent users to reboot the router with internet disconnected
# in order to disable DNS blockage
# it will check for <hname>.gz in $PERSISTENTDIR and unpack those to $ACTIVEHOSTDIR/<hname>
# since <hname> can be a symlink the file may be stored elsewhere
restore_persistent_hostfiles() {
        for f in $(ls -1 $PERSISTENTDIR/*.gz) ; do
                # link all host files (symlinks and real host files) to $ACTIVEHOSTDIR
                # host files in gz format get decompressed and written to the corresponding
                # files/symlinks in $PERSISTENTDIR
		hfn=$(basename $f .gz)
		if [ "$(readlink $PERSISTENTDIR/$hfn)" == "$ACTIVEHOSTDIR/$hfn" ] ; then
			logger "$PERSISTENTDIR/$hfn is already a symlink to $ACTIVEHOSTDIR/$hfn"
		else	
                        logger "Linking $ACTIVEHOSTDIR/$hfn to persistent host file $PERSISTENTDIR/$hfn"
                        ln -sf $PERSISTENTDIR/$hfn $ACTIVEHOSTDIR/$hfn
        	fi
                if is_hostfile_consistent "$hfn" ; then
                        logger "$PERSISTENTDIR/$hfn already consistent, no unpacking needed"
                else
                        logger "Unpacking persistent host file $f to $PERSISTENTDIR/$hfn"
                        unpack_hostfile "$f" > $PERSISTENTDIR/$hfn
                fi
	  done
}

### save_persistent_hostfiles
# this function is used after an update from a remote host file
# and will update the permanently stored compressed host files
# it will check for *.gz files in $PERSISTENTDIR and update just those
save_persistent_hostfiles() {
        for f in $(ls -1 $PERSISTENTDIR/*.gz) ; do 
                # update all existing compressed host files from their corresponding files/symlinks
                if test -e $PERSISTENTDIR/$(basename $f .gz); then
                        if is_hostfile_consistent "$(basename $f .gz)"; then
                                logger "Skip $f, contents already consistent"
                        else
                                # TODO keep existing '#' comments and white listed items in orig gz
                                # FIXME for now these get deleted
                                logger "Compressing updated host file to $f"
			        cat $PERSISTENTDIR/$(basename $f .gz) | awk '{print $NF}' | gzip -c > $f
                        fi
                fi
        done
}

### last_mtime
# helper function to check the last modification time of the remote host file and 
# returns a time stamp, if not accessible it returns -1
# $1 -- URL to the remote host file
last_mtime() {
        curl -m 20 -sI $1 | awk '/^HTTP\//{if ($2!=200) exit(1)}/^Last-Modified:/{$1="";mtime=$0}END{print mtime}' |\
        awk 'BEGIN{split("Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec",m); for (i in m) {mn[m[i]]=i}}
             {hhmmss=gensub(/:/," ","g",$5);print mktime(""$4" "mn[$3]" "$2" "hhmmss)}'
}

### update_dnsmasq_cfg
# copy the tld mask rules from $RULESDIR and filter the whitelisted ones
update_dnsmasq_cfg() {
	logger "Rewriting using address rules from $RULESDIR..."
	for f in $(ls -1 $RULESDIR/*) ; do
		cat $f | awk '{print "address=/"$1"/"'$ENDPOINT_IP4'}' > /tmp/dnsmasq.d/$(basename $f)
	done
	# TODO whitelist support
}

### signal_dnsmasq
# Signals a running dnsmasq instance to re-read host files contained in $ACTIVEHOSTDIR
# If dnsmasq is not running it will be restarted
# Run this once after finishing all 'update_active_hostfile' (/etc/inithost.cfg) calls
signal_dnsmasq() {
        if ps -w | grep dns[m]asq; then
                killall -HUP dnsmasq
        else
                /etc/init.d/dnsmasq restart
        fi
}

boot() {
        logger "install iptable rules to force dnsmasq routing for port 53 queries"
        # route every DNS query through dnsmasq
        LAN_IP=$(uci get network.lan.ipaddr) # FIXME make fail safe
        iptables -t nat -A PREROUTING -i br-lan -p tcp --dport 53 -j DNAT --to $LAN_IP
        iptables -t nat -A PREROUTING -i br-lan -p udp --dport 53 -j DNAT --to $LAN_IP

        logger "make sure host directories exist"
        mkdir -p $PERSISTENTDIR
        mkdir -p $ACTIVEHOSTDIR
	start
}

restart() {
	stop
	start
}

start() {
        logger "Start and activate dnsmasq blocking of ads and porn sites"
        restore_persistent_hostfiles
	logger "Activate persistent host files..."
	signal_dnsmasq
        reload
}

reload() {
        logger "Retrieve updated host files from web..."
        update_hostfiles_from_web
        signal_dnsmasq
        logger "...done"
        logger "Make updated host settings persistent..."
        save_persistent_hostfiles
	logger "...done"
}

stop() {
        logger "Stopping host blocking..."
        # TODO delete tmp host files
        # shutdown dnsmasq if still running
        # delete iptables rules
        logger "...done"
}

# TODO that's how to get yoyo dnsmasq tld ruleset... check if those can be more useful...
# wget -O /etc/dnsmasq.d/adblock.conf "http://pgl.yoyo.org/adservers/serverlist.php?hostformat=dnsmasq&showintro=0&mimetype=plaintext" && service dnsmasq restart