private void build(ImageSegment segment) throws IOException {
SortedSet<ImageSegment> set = segments.get(segment.getId());
if (set == null) {
set = new TreeSet<>();
segments.put(segment.getId(), set);
}
set.add(segment);
segment = set.last();
if (segment.isLast() && set.size() > segment.getIndex()) {
segments.remove(segment.getId());
build(set);
}
}
