#!/usr/bin/env bash

# Title               : mcast_converter
# Last modified date  : 12.04.2023
# Author              : Martin Tonusoo
# Description         : Script converts IPv4 multicast address to
#                       multicast MAC address or multicast MAC
#                       address to IPv4 multicast addresses depending
#                       on the input.
# Options             : IPv4 multicast address or multicast MAC address.
# Notes               :


# 224.0.0.0 - 239.255.255.255
read -r mip_regex << EOF
^2(2[4-9]|3[0-9])\.\
(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]?|0)\.\
(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]?|0)\.\
(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]?|0)$
EOF


# 01:00:5e:00:00:00 - 01:00:5e:7f:ff:ff
read -r mac_regex << EOF
^01:00:5e:\
([0-7][0-9a-f]):\
([0-9a-f]{2}):\
([0-9a-f]{2})$
EOF


if [[ "$1" =~ $mip_regex ]]; then

	for (( n="${BASH_REMATCH[2]}"; n>0; n >>= 1 )); do
		o2_bits="$(( n & 1 ))$o2_bits"
	done

	printf -v o2_bits "%08d" "$o2_bits"
	o2_bits="0${o2_bits:1}"

	printf "%s:%02x:%02x:%02x\n" \
						"01:00:5e" \
						"$(( 2#$o2_bits ))" \
						"${BASH_REMATCH[3]}" \
						"${BASH_REMATCH[4]}"

elif [[ "$1" =~ $mac_regex ]]; then

	o4_dec=$(( 16#"${BASH_REMATCH[1]}" ))

	for (( n="$o4_dec"; n>0; n >>= 1 )); do
		o4_bits="$(( n & 1 ))$o4_bits"
	done

	printf -v o4_bits "%08d" "$o4_bits"
	o4_bits="${o4_bits:1}"

	for bits in {0..1}{0..1}{0..1}{0..1}{0..1}; do

		printf "%d.%d.%d.%d\n" \
				$(( 2#"1110${bits:0:4}" )) \
				$(( 2#"${bits:4:1}$o4_bits" )) \
				$(( 16#"${BASH_REMATCH[2]}" )) \
				$(( 16#"${BASH_REMATCH[3]}" ))

	done

else

	printf "%s\n%s\n" \
		"Invalid multicast MAC or IPv4 address" \
		"Examples: '${0##*/} 01:00:5e:00:99:0a' or '${0##*/} 239.1.2.100'" >&2
	exit 1

fi