#!/bin/sh
# Manage uid/gid maps for containers
#
# This script manages uids/gids assigned to certain containers or groups of containers. It uses /etc/subuid and
# /etc/subgid by default to save the information. All the ranges are owned by root as we don't want to support creation
# of containers by unprivileged users, but rather want to create unprivileged containers as root user.

USER_ID=0
FIRST_ID=1000000
DEFAULT_COUNT=65536
FILENAME="/etc/sub_____id"

get_filename () (
	TYPE="${1}"
	echo "${FILENAME}" | sed "s/_____/${TYPE}/"
)

find_range () (
	TYPE="${1}"
	NAME="${2}"
	FILENAME="$(get_filename ${TYPE})"

	grep -A 1 "^# ${NAME}$" "${FILENAME}" -A 1 | tail -n 1
)

get_last_range () (
	TYPE="${1}"
	grep "^${USER_ID}:" "$(get_filename ${TYPE})" | tail -n 1
)

get_new_range () (
	TYPE="${1}"
	LAST_RANGE=$(get_last_range "${TYPE}")
	if [ "${LAST_RANGE}" = "" ]; then
		NEW_ID=$FIRST_ID;
	else
		LAST_ID=$(echo "${LAST_RANGE}" | cut -d : -f 2)
		LAST_COUNT=$(echo "${LAST_RANGE}" | cut -d : -f 3)
		NEW_ID=$(( $LAST_ID + $LAST_COUNT ))
	fi
	echo "${USER_ID}:${NEW_ID}:${DEFAULT_COUNT}"
)

append_range () (
	TYPE="${1}"
	FILENAME="$(get_filename ${TYPE})"
	NAME="${2}"
	RANGE="${3}"
	printf "# ${NAME}\n${RANGE}\n" >> "${FILENAME}"
)

usage () {
	echo "usage: get-lxc-idmap-config <u|g> <container-group-name>"
	exit 1
}


TYPE="${1}"
if [ "${TYPE}" = "" ] || [ "${TYPE}" = "--help" ] || [ "${TYPE}" = "-h" ]; then
	usage
fi

NAME="${2}"
if [ "${NAME}" = "" ]; then
	usage
fi

RANGE=$(find_range "${TYPE}" "${NAME}")

if [ "${RANGE}" = "" ]; then
	RANGE=$(get_new_range "${TYPE}")
	if [ "${RANGE}" = "" ]; then
		exit 1
	fi
	append_range "${TYPE}" "${NAME}" "${RANGE}"
fi

RANGE_START=$(echo ${RANGE} | cut -d : -f 2)
RANGE_COUNT=$(echo ${RANGE} | cut -d : -f 3)
printf "lxc.idmap = %s 0 %s %s\n" "${TYPE}" "${RANGE_START}" "$(( ${RANGE_COUNT} - 1))"