#!/bin/sh
set -f

src='-' dst='-'
case $# in
0 ) ;;
1 )
	src="$1"
	case "$1" in
	*.in ) dst="${1%".in"}" ;;
	esac
;;
2 ) src="$1" ; dst="$2" ;;
* ) exit 1 ;;
esac
[ -n "${src}" ] || exit 1
[ -n "${dst}" ] || exit 1
if [ "${src}" = '-' ] ; then src=/dev/stdin ; fi
if [ "${dst}" = '-' ] ; then dst=/dev/stdout ; fi

is_same_file() {
	find -L "$1" -samefile "$2" -printf . -quit 2>/dev/null | grep -Fq . || return 1
}

if is_same_file "${src}" /dev/stdin ; then src=/dev/stdin ; fi
if is_same_file "${dst}" /dev/stdout ; then dst=/dev/stdout ; fi

while : ; do
	if [ "${src}" = '/dev/stdin' ] && [ "${dst}" = '/dev/stdout' ] ; then
		break
	fi

	if is_same_file "${src}" "${dst}" ; then
		exit 1
	fi
break ; done

set +e ; unset __ret
while [ -n "${ENVSUBST_ARGS}" ] ; do
	[ -f "${ENVSUBST_ARGS}" ] || break
	[ -s "${ENVSUBST_ARGS}" ] || break

	envsubst "$(cat "${ENVSUBST_ARGS}" </dev/null)" < "${src}" > "${dst}"
	__ret=$?
break ; done
if [ -z "${__ret}" ] ; then
	envsubst "$(envsubst-args.sh </dev/null)" < "${src}" > "${dst}"
	__ret=$?
fi

while : ; do
	[ "${ENVSUBST_UNLINK_SRC}" = 1 ] || break
	[ "${src}" != '/dev/stdin' ] || break

	rm -f "${src}"
break ; done

exit ${__ret}