#!/usr/bin/env bash
set -euo pipefail

if [[ $# -ne 0 ]]; then
	echo "Usage: $0" >&2
	exit 2
fi
if [[ ${EUID} -ne 0 ]]; then
	echo "Run this rollback tool as root." >&2
	exit 2
fi

install_root="${NETFISHING_INSTALL_ROOT:-/opt/netfishing-server}"
service_name="${NETFISHING_SERVICE_NAME:-netfishing-server.service}"
releases_dir="${install_root}/releases"

if [[ "${install_root}" != /* || "${install_root}" == "/" ]]; then
	echo "NETFISHING_INSTALL_ROOT must be a specific absolute directory." >&2
	exit 2
fi
if [[ ! -L "${install_root}/current" || ! -L "${install_root}/previous" ]]; then
	echo "Both current and previous release links are required." >&2
	exit 1
fi

current_target="$(readlink -f -- "${install_root}/current")"
previous_target="$(readlink -f -- "${install_root}/previous")"
for target in "${current_target}" "${previous_target}"; do
	if [[ ! -d "${target}" || "${target}" != "${releases_dir}/"* ]]; then
		echo "Refusing to use a release outside ${releases_dir}." >&2
		exit 1
	fi
	(cd -- "${target}" && sha256sum -c SHA256SUMS)
done

replace_symlink() {
	local target="$1"
	local link_path="$2"
	local temporary_link="${install_root}/.$(basename -- "${link_path}").new.$$"
	ln -s -- "${target}" "${temporary_link}"
	mv -Tf -- "${temporary_link}" "${link_path}"
}

service_active=false
if systemctl is-active --quiet "${service_name}"; then
	service_active=true
	systemctl stop "${service_name}"
fi

replace_symlink "${previous_target}" "${install_root}/current"
replace_symlink "${current_target}" "${install_root}/previous"

if ${service_active}; then
	if ! systemctl start "${service_name}"; then
		start_succeeded=false
	else
		sleep 1
		start_succeeded=true
		systemctl is-active --quiet "${service_name}" || start_succeeded=false
	fi
	if ! ${start_succeeded}; then
		echo "Rollback target failed to start; restoring the original release." >&2
		replace_symlink "${current_target}" "${install_root}/current"
		replace_symlink "${previous_target}" "${install_root}/previous"
		systemctl start "${service_name}" || true
		exit 1
	fi
fi

echo "Rolled back to $(basename -- "${previous_target}")."