#!/usr/bin/env bash

# Usage:
#	configLine [searchPattern] [replaceLine] [filePath]
# Ref https://stackoverflow.com/a/54909102/1460422
config_line() {
	local OLD_LINE_PATTERN NEW_LINE NEW FILE
	OLD_LINE_PATTERN="$1"; shift
	NEW_LINE="$1"; shift
	FILE="$1"
	NEW="$(echo "${NEW_LINE}" | sed 's/\//\\\//g')";
	
	touch "${FILE}"
	sed -i '/'"${OLD_LINE_PATTERN}"'/{s/.*/'"${NEW}"'/;h};${x;/./{x;q100};x}' "${FILE}"
	if [[ $? -ne 100 ]] && [[ ${NEW_LINE} != '' ]]
	then
		echo "${NEW_LINE}" >> "${FILE}"
	fi
}

log_msg() {
	echo -e "[ ${HOSTNAME} ] [ $(date -u +"%Y-%m-%dT%H:%M:%SZ") ] $*" >&2;
}

# Old approach - we've learned we can override /etc/network/interfaces via /etc/dhcp/dhclient.conf
# config_line "dns-nameservers" "dns-nameservers 172.16.230.100" "/etc/network/interfaces";

completed_file="/etc/dhcp/sbrl-dns-configured";

log_msg "Configuring DNS nameserver";
if [[ ! -f "${completed_file}" ]]; then
	log_msg "DNS nameserver not yet configured, appending to /etc/dhcp/dhclient.conf";
	echo "interface \"eth0\" {
	supersede domain-name-servers 172.16.230.100;
}" | sudo tee -a /etc/dhcp/dhclient.conf;
	sudo touch "${completed_file}";
	
	log_msg "Complete, this machine needs a reboot to activate the new config directives";
else
	log_msg "DNS nameserver config written already, no changes made";
fi