#!/bin/bash

#
# simplify-subnets.sh
#
# Developed by Ondrej Jombik <nepto@platon.sk>
# Copyright (c) 2018 Platon Group, http://platon.sk/
# Licensed under terms of GNU General Public License.
# All rights reserved.
#
# Changelog:
# 2018-05-07 - created
# 2018-05-08 - merging multiple C-class into one B-class
#              based on C-class subnets counting
#

# $Platon: scripts/shell/firewall/firewall.d/subnets/simplify-subnets.sh,v 1.6 2018/05/08 00:51:39 nepto Exp $

# Minimum amount of C-classes to be merged into one B-class
MIN_C_CLASS_MERGE=120;
SUBNET_FILE="$1";

if [ -z "$SUBNET_FILE" ]; then
	echo "Usage: $0 <sorted-file>";
	exit 1;
fi

# Simple subnet implementation of pow()
# It returns 1 for /24, 2 for /23, 4 for /22, and so on
c_class_subnets_count () # {{{
{
	local pow ret i
	pow=$(( 24 - $1 ))
	ret=1
	i=1
	while [ $i -le $pow ]; do
		ret=$(( ret * 2 ))
		i=$(( i + 1 ))
	done
	echo $ret;
} # }}}

prev_C='';
prev_B='';
cnt_CinB=1;

while IFS='' read -r line; do
	if [ -z "$line" -o "${line#\#}"x != "${line}x" ]; then
		echo "$line";
		continue;
	fi

	subnet="`echo "$line" | cut -f1 -d/`";
	mask="`echo "$line" | cut -f2 -d/`";
	if [ "$mask" -gt 24 ]; then
		mask=24;
	fi

	subnet_C="`echo "$subnet" | sed 's/\.[0-9]\+$/.0/'`";
	subnet_B="`echo "$subnet" | sed 's/\.[0-9]\+\.[0-9]\+$/.0.0/'`";

	if [ -z "$to_write" ]; then
		prev_C="$subnet_C";
		prev_B="$subnet_B";
		to_write="$subnet_C/$mask";
	fi

	if [ "$subnet_C" = "$prev_C" ]; then
		continue;
	fi

	if [ "$subnet_B" = "$prev_B" ]; then
		to_write="$to_write"$'\n'; # newline
		to_write="$to_write$subnet_C/$mask";
		prev_C="$subnet_C";
		# /24=1, /23=2, /22=4, /21=8, ...
		subnet_count="`c_class_subnets_count $mask`";
		cnt_CinB=$(( cnt_CinB + subnet_count ));
		continue;
	fi

	# Output
	if [ "$cnt_CinB" -gt "$MIN_C_CLASS_MERGE" ]; then
		echo "# Merged $cnt_CinB C-classes into one B-class";
		echo "$prev_B/16";
	else
		if [ "$cnt_CinB" -gt 1 ]; then
			echo "# Found $cnt_CinB similar networks";
			echo "$to_write";
		else
			if [[ "$to_write" = */24 ]]; then
				echo "# Simplified to C-class";
				echo "$to_write";
			else
				echo "# Unchanged network";
				echo "$to_write";
			fi
		fi
	fi

	to_write="$subnet_C/$mask";
	prev_B="$subnet_B";
	prev_C="$subnet_C";
	cnt_CinB=1;
done < "$SUBNET_FILE";