#!/bin/sh

export PATH="/usr/bin:/bin"

error() {
	: ${ERR:=1}
	echo "$@" >&2
	return "$ERR"
}

alt_ab() {
	if [ "$1" == "a" ]; then echo "b"; else echo "a"; fi
}

: ${S6_PATH:='/etc/s6'}
: ${S6_RC_PATH:="$S6_PATH/rc"}
: ${S6_SV_PATH:="$S6_PATH/sv"}

# A/B mode, always keep last copy
DB_FRESH_ACT=""
DB_FRESH_NAC=""

cstate() {
	DB_FRESH_ACT="$(readlink "$S6_SV_PATH/current" | cut -d. -f2)" # if it fails (missing), it will be empty and 'a' will be used as inactive by default
	DB_FRESH_NAC="$(alt_ab "$DB_FRESH_ACT")"
}

generate() {
	mkdir -p "$S6_SV_PATH" || ERR="$?" error "Failed to create sv directory"

	# A/B current
	if [ -d "$S6_SV_PATH/current.$DB_FRESH_NAC" ]; then
		rm -rf "$S6_SV_PATH/current.$DB_FRESH_NAC" || ERR="$?" error "Failed to remove inactive database path"
	fi
	s6-rc-compile "$S6_SV_PATH/current.$DB_FRESH_NAC" "$S6_RC_PATH"/* || ERR="$?" error "Failed to compile current s6 database"
}

update() {
	s6-rc-update "$S6_SV_PATH/current.$DB_FRESH_ACT" || ERR="$?" "Failed to update live state of the database"
}

swap() {
	ln -sfn "current.$DB_FRESH_NAC" "$S6_SV_PATH/current" || ERR="$?" "Failed to update A/B current symlink"
}

for act in $@; do
	cstate
	if [ "$act" == "generate" ]; then
		generate
	elif [ "$act" == "update" ]; then
		update
	elif [ "$act" == "swap" ]; then
		swap
	else
		error "Action must be generate, update or swap"
	fi
done