#! @shell@

WORKING_DIRECTORY=$(mktemp -d "${TMPDIR:-/tmp}"/nix-reduce-build-XXXXXX);
cd "$WORKING_DIRECTORY";

if test -z "$1" ; then
	echo 'nix-reduce-build (paths or Nix expressions) -- (logins at remote computers)' >&2
	echo As in: >&2
	echo nix-reduce-build /etc/nixos/nixos -- user@somewhere.nowhere.example.org >&2
	exit;
fi;

while ! test "$1" = "--" || test "$1" = "" ; do 
	echo "$1" >> initial; >&2
	shift;
done
shift;
echo Will work on $(cat initial | wc -l) targets. >&2

while read ; do
	case "$REPLY" in 
		${NIX_STORE_PATH:-/nix/store}/*)
			echo "$REPLY" >> paths; >&2
			;;
		*)
			nix-instantiate "$REPLY" >> paths;
			;;
	esac;
done < initial;
echo Proceeding $(cat paths | wc -l) paths. >&2

while read; do
	case "$REPLY" in
		*.drv)
			echo "$REPLY" >> derivers; >&2
			;;
		*)
			nix-store --query --deriver "$REPLY" >>derivers;
			;;
	esac;
done < paths;
echo Found $(cat derivers | wc -l) derivers. >&2

cat derivers | xargs nix-store --query -R > derivers-closure;
echo Proceeding at most $(cat derivers-closure | wc -l) derivers. >&2

cat derivers-closure | egrep '[.]drv$' | xargs nix-store --query --outputs > wanted-paths;
cat derivers-closure | egrep -v '[.]drv$' >> wanted-paths;
echo Prepared $(cat wanted-paths | wc -l) paths to get. >&2

cat wanted-paths | xargs nix-store --check-validity --print-invalid > needed-paths;
echo We need $(cat needed-paths | wc -l) paths. >&2

if test -z "$1" ; then
	cat needed-paths;	
fi;

for i in "$@"; do 
	cat needed-paths | while read; do 
		nix-copy-closure --from "$i" --gzip "$REPLY" </dev/null || true; 
	done;
	mv needed-paths wanted-paths;
	cat wanted-paths | xargs nix-store --check-validity --print-invalid > needed-paths;
	echo We still need $(cat needed-paths | wc -l) paths. >&2
done;

cd /
rm -r "$WORKING_DIRECTORY"