// A is the user object associated with each mask (aka a "label")
sclass G22HashedMasks<A> {
  record noeq Mask(Image2B image, A label) {
    long hash;
    
    public long hashCode() {
      if (hash == 0)
        hash = hashImage2B(image);
      ret hash;
    }
  }

  settable WidthAndHeight maskSize;
  new Map<Long, Mask> masksByHash;
  new MultiSet<A> labels;

  // default mask size
  { maskSize(16); }
  
  selfType maskSize(int size) {
    ret maskSize(widthAndHeight(size));
  }
  
  Image2B regionToMaskImage(IImageRegion region) {
    ret toImage2B(scaledIBinaryImage(maskSize, regionToIBinaryImage(region)));
  }
  
  void addRegion(IImageRegion region, A label) {
    var mask = new Mask(regionToMaskImage(region), label);
    var existingMask = masks.get(mask.hashCode());
    if (existingMask != null)
      labels.remove(existingMask.label);
      existingMask.label = combineLabels(existingMask.label, mask.label);
      mask = existingMask;
    } else
      masks.put(mask.hashCode(), mask);
    ghost_cache = null;
    certainty_cache = null;
    labels.add(mask.label);
  }
  
  swappable A combineLabels(A a, A b) {
    if (a == null) ret b;
    if (b == null) ret a;
    if (eq(a, b)) ret a;
    fail("Label conflict: " + a + " / " + b);
  }
  
  L<Image2B> maskImages() {
    ret map(masks, mask -> mask.image);
  }
  
  BufferedImage masksSquare() {
    ret mergeBufferedImagesAsSquare(allToBufferedImage(maskImages()));
  }
  
  toString {
    ret renderVars(shortClassName(this), +maskSize, masks := n2(masks));
  }
  
  simplyCached FloatBWImage ghost() {
    ret preciseAverageOfBinaryImages(maskImages());
  }
  
  simplyCached double certainty() {
    ret preciseCertaintyImage(ghost()).averageBrightness();
  }
}