#!/usr/bin/env bash

# Title               : rm-expired-prefixes
# Last modified date  : 16.03.2023
# Author              : Martin Tonusoo
# Description         : Script removes expired "prefix" statements from
#                       /etc/radvd.conf file based on the expiration
#                       field(ISO 8601 timestamp) at the end of "prefix"
#                       line. The expiration field is added to the "prefix"
#                       statements by dhclient exit hook.
# Options             :
# Notes               :

radvd_conf="/etc/radvd.conf"
new_radvd_conf="${radvd_conf}.rm-expired-prefixes.$$"

while IFS= read -r line; do

	case "$line" in
		"    prefix "*)
			# Add the "prefix" statement if its timestamp
			# is in the future.
			if [[ "${line##* }" > $(date --iso-8601="seconds") ]]; then
				echo "$line"
			else
				prefix="${line%% \{*}"
				logger -t "rm-expired-prefixes" -p daemon.info \
				"INFO: Removed expired ${prefix#    } from $radvd_conf"
			fi
			;;
		*)
			echo "$line"
			;;
	esac

done < "$radvd_conf" >> "$new_radvd_conf"

chown --reference="$radvd_conf" "$new_radvd_conf"
chmod --reference="$radvd_conf" "$new_radvd_conf"

mv -f "$new_radvd_conf" "$radvd_conf"

systemctl is-active --quiet radvd.service && systemctl reload radvd.service