#!/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'}
: ${S6_DIST_PATH:="$S6_PATH/dist"}
: ${S6_RC_PATH:="$S6_PATH/rc"}
: ${S6_ENV_PATH:="$S6_PATH/env"}
: ${S6_SV_PATH:="$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="$?" error "Failed to update live state of the database"
}

swap() {
	[ -d "$S6_SV_PATH/current.$DB_FRESH_NAC" ] || error "There's no database to switch to"

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

dist() {
	SDIR="$S6_DIST_PATH/rc" DPATH="$S6_RC_PATH" distdefs
	SDIR="$S6_DIST_PATH/env" DPATH="$S6_ENV_PATH" distdefs
}

distdefs() {
	[ -z "$SDIR" ] && error "SDIR not defined"
	[ -z "$DPATH" ] && error "DPATH not defined"
	for cdir in "$SDIR"/*; do
		local srv="${cdir##*/}"
		local dsv="$DPATH/$srv"
		if [ ! -e "$dsv" ]; then
			ln -sv "$cdir" "$dsv" || ERR="$?" error "Failed to create reference"
		fi
	done
}

custom() {
	local SVC="$1"
	[ -e "$S6_RC_PATH/$SVC" ] || error "Service $SVC doesn't exist"
	[ -h "$S6_RC_PATH/$SVC" ] || error "Service $SVC is already a custom instance"
	rm -rf "$S6_RC_PATH/$SVC"
	cp -r "$S6_DIST_PATH/rc/$SVC" "$S6_RC_PATH/$SVC"
}

cmd="$1"
shift
cstate
case "$cmd" in
	generate|update|swap|dist|custom) eval "$cmd" $@;;
	*) error "Invalid command $cmd";;
esac