#!/bin/sh
set -eu

usage() {
	cat <<-'EOF'
		Usage:
		  until [-n SECONDS] -- COMMAND...
		  until -h
	EOF
}

help() {
	cat <<-'EOF'

		Options:
		  -n SECONDS    the amount of seconds to sleep between
				attempts (default: 5)
		  -h, --help    show this message


		Runs COMMAND until it eventually succeeds.  Sleep SECONDS
		between attempts.


		Examples:

		  Try flaky build until it succeeds:

		    $ until guix home build home.scm


		  Try to build until a new version is successfull,
		  waiting 30 seconds between attempts:

		    $ until -n 30 -- x git pull AND make
	EOF
}


for flag in "$@"; do
	case "$flag" in
		--)
			break
			;;
		--help)
			usage
			help
			exit
			;;
		*)
			;;
	esac
done

_SECONDS=5
while getopts 'n:h' flag; do
	case "$flag" in
		n)
			_SECONDS="$OPTARG"
			;;
		h)
			usage
			help
			exit
			;;
		*)
			usage >&2
			exit 2
			;;
	esac
done
shift $((OPTIND - 1))


ATTEMPT=1
while true; do
	printf 'Attempt %s.\n' "$ATTEMPT" >&2
	ATTEMPT=$((ATTEMPT + 1))
	if "$@"; then
		break
	fi
	sleep "$_SECONDS"
done