import java.util.HashMap;
import java.util.Map;
import java.util.Optional;
import java.util.function.Supplier;

public class SnapshotUtil {

    public static Map<String, FileSystemLocationSnapshot> indexByAbsolutePath(FileSystemSnapshot snapshot) {
        HashMap<String, FileSystemLocationSnapshot> index = new HashMap<>();
        snapshot.accept(entrySnapshot -> {
            index.put(entrySnapshot.getAbsolutePath(), entrySnapshot);

        }

        @Override
        public FileCollectionInternal createDelegate() {
            List<File> outputs = previousOutputs.values().stream()
                .map(SnapshotUtil::indexByAbsolutePath)
                .map(Map::keySet)
                .flatMap(Collection::stream)
                .map(File::new)
                .collect(Collectors.toList());