// an indexing structure for grayscale images

// -all images have the same size

// -images are sorted by

//   1. average brightness

//   2. "lexical" scanline ordering (within same brightness)

// -every image can have an arbitrary value associated (type "A")

persistable sclass ScaledGrayscaleCache<A> extends Meta is WidthAndHeight, IntSize {

  int w, h;

  new TreeSet<Entry> entries;

  persistable class Entry is Comparable<Entry> {

    double brightness;

    BWImage image;

    settable A value;

    *(BWImage *image) {

      brightness = image.averageBrightness();

    }

    public int compareTo(Entry e) {

      if (brightness != e.brightness)

        ret cmp(brightness, e.brightness);

      ret compareBWImagesByScanlineOrdering(image, e.image);

    }

  }

  *(int w) { this(w, w); }

  *(int *w, int *h) {}

  public int getWidth() { ret w; }

  public int getHeight() { ret h; }

  // returns true if image was new

  bool add(IBWImage image) {

    BWImage scaledImage = scaledBWImageFromBWIntegralImage(w, h, image);

    var entry = new Entry(scaledImage);

    var existingEntry = entries.floor(entry);

    if (cmp(entry, existingEntry) == 0)

      false;

    entries.add(entry);

    true;

  }

  public int size() { ret entries.size(); }

}