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

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

shopt -s extglob

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

hetzcurl() {
	curl -sfH "Auth-API-Token: ${HETZNER_TOKEN}" \
		"https://dns.hetzner.com/api/v1/${1}" \
		"${@:2}"
}

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

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

res="$(hetzcurl "zones")" || die 'Zones lookup failed'
IFS='|' read zone_id zone_name < <(jq -er --arg re "${zone_re}" \
	'[.zones[] | select(.name | test("\\A" + $re + "\\z"))] |
		if . == [] then (null | halt_error) else . end |
		max_by(.name | length) | [.id, .name] | join("|")' \
	<<< "${res}") || die 'Zone not found'
rec_name="${TARGET%%?(.)${zone_name}}"
rec_name="${rec_name:-@}"

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

res="$(hetzcurl "records/${rec_id}")" || die 'Record lookup failed'
old_ip="$(jq -r '.record.value' <<< "${res}")"

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

data="$(jq -c --arg ip "${ip}" \
	'.record | {zone_id, type, name, value: $ip }' <<< "${res}")"
res="$(hetzcurl "records/${rec_id}" \
	-H 'Content-Type: application/json' \
	-X PUT -d "${data}")" || die 'Record update failed'
new_ip="$(jq -r '.record.value' <<< "${res}")"

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