#!/usr/bin/env bash
#
# Copyright 2022 David Vazgenovich Shakaryan
#
# LINODE_TOKEN=<token> linode-ddns.sh <domain>

IP_RESOLVER='https://ifconfig.co'
TARGET="${1}"

shopt -s extglob

die() {
	[[ -n "${@}" ]] && echo "${@}" >&2
	exit 1
}

lincurl() {
	curl -sfH "Authorization: Bearer ${LINODE_TOKEN}" \
		"https://api.linode.com/v4/domains/${1}" \
		"${@:2}"
}

ip="$(curl -sf4 "${IP_RESOLVER}")" || die 'IP lookup failed'

dom_re="${TARGET}"
while [[ "${dom_re}" =~ ^([^\\]*)\.(.*)$ ]]; do
	dom_re="(${BASH_REMATCH[1]}\\.)?${BASH_REMATCH[2]}"
done

res="$(lincurl)" || die 'Domains lookup failed'
IFS='|' read dom_id dom_name < <(jq -er --arg re "${dom_re}" \
	'[.data[] | select(.domain | test("\\A" + $re + "\\z"))] |
		if . == [] then (null | halt_error) else . end |
		max_by(.domain | length) | [.id, .domain] | join("|")' \
	<<< "${res}") || die 'Domain not found'
rec_name="${TARGET%%?(.)${dom_name}}"

res=$(lincurl "${dom_id}/records") || die 'Records lookup failed'
rec_id="$(jq -er --arg name "${rec_name}" \
	'first(.data[] | select(.type == "A" and .name == $name)) | .id' \
	<<< "${res}")" || die 'Record not found'

res="$(lincurl "${dom_id}/records/${rec_id}")" || die 'Record lookup failed'
old_ip="$(jq -r '.target' <<< "${res}")"

if [[ "${old_ip}" == "${ip}" ]]; then
	echo "IP unchanged from ${ip}"
	exit
fi

res="$(lincurl "${dom_id}/records/${rec_id}" \
	-H 'Content-Type: application/json' \
	-X PUT -d "{\"target\":\"${ip}\"}")" || die 'Record update failed'
new_ip="$(jq -r '.target' <<< "${res}")"

echo "IP changed from ${old_ip} to ${new_ip}"