#!/bin/bash

debug=false
#debug=true

function Init
	{

	# constants
	cidr_input_file="./input.list"
	cidr_output_file="./output.list"
	default_maskvalue=24

	# variables
	prev_first3=""
	prev_octet4=""
	prev_comment=""
	match_found=false
	prev_match_found=false
	prev_has_been_written=false
	current_maskvalue=0
	active_maskvalue=0
	exitcode=0

	}

function CondenseOnThreeOctets
	{

	$verbose && echo -n "["$(date)"] -- applying CIDR mask where possible ..."

	# delete and create a new output file
	rm -f "${cidr_output_file}" && touch "${cidr_output_file}"

	while read line ; do
		if [ ! -z "$line" ] ; then				# ignore empty lines
			if [[ $line != \#* ]] ; then        # ignore lines that begin with a # character
				# only take first word on each line as IP address
				current_ip=$( cut -f1 <<< "${line}" )

				# take everything after /* as a comment but only if it exists
				[[ ${line} == */\** ]] && comment=$( sed 's|^.*/\*|/\*|' <<< "${line}" ) || comment=""

				while IFS=. read octet1 octet2 octet3 octet4 ; do
					$debug && echo

					first3="${octet1}.${octet2}.${octet3}"
					$debug && echo "-- now checking - IP entry: ${first3}.${octet4}"

					if [ -z "$prev_first3" ] ; then
						# first time through the loop - no previous values have been saved yet.
						SaveThisIpAsPrev
					else
						if [ "$first3" = "$prev_first3" ] ; then
							# if here then first 3 octets matched so we can combine this IP with the previous IP
							match_found=true
							SaveThisIpAsPrev
						else
							# if here then first3 octets are different so it's OK to save the previous IP
							match_found=false
							WriteIpAsCIDR
						fi
					fi
				done <<< "${current_ip}"
			fi
		fi
	done < "${cidr_input_file}"

	# write out last IP
	WriteIpAsCIDR

	$verbose && echo " done!"

	}

function CalcMasks
	{

	[[ $active_maskvalue -eq 0 ]] && active_maskvalue=${default_maskvalue}

	if [[ $octet4 == *"0/"* ]] ; then
		current_maskvalue=${octet4:2}
		[[ $current_maskvalue -lt $active_maskvalue ]] && active_maskvalue=${current_maskvalue}
	else
		current_maskvalue=0
	fi

	}

function SaveThisIpAsPrev
	{

	$debug && echo "-- saving current IP as previous IP"

	CalcMasks

	prev_first3=$first3
	prev_octet4=$octet4
	prev_comment="$comment"
	prev_match_found=$match_found
	prev_has_been_written=false

	}

function WriteIpAsCIDR
	{

	if [ ! -z "$prev_first3" ] ; then
		if ! $prev_has_been_written ; then
			if $prev_match_found ; then
				buildline="$prev_first3.0/$active_maskvalue\t$prev_comment"
			else
				buildline="$prev_first3.$prev_octet4\t$prev_comment"
			fi

			echo -e "${buildline}" >> "${cidr_output_file}"

			prev_has_been_written=true
			active_maskvalue=0
		fi
	fi

	SaveThisIpAsPrev

	}

echo "["$(date)"] >> started [$0@$HOSTNAME]"

Init
CondenseOnThreeOctets

echo "["$(date)"] << finished [$0@$HOSTNAME]"

exit $exitcode