// type parameter is rect + FEN
// not persistable
sclass ChessOCR_TwoStageRecognizer extends SteppableAndBest<Pair<Rect, S>> {
  replace Segmenter with IF1<BufferedImage, L<Rect>>.
  
  // input
  BufferedImage inputImage;
  Iterator<? extends Segmenter> segmenterStream;
  ChessPieceRecognizer pieceRecognizer;
  bool verbose;
  
  // internal
  L<Rect> rectQueue = syncLinkedList();
  new Set<Rect> rectsTried;

  *() {}
  *(ChessPieceRecognizer *pieceRecognizer, BufferedImage *inputImage, Iterator<? extends Segmenter> *segmenterStream) {}
  
  public bool step() {
    if (nempty(rectQueue))
      ret true with tryRect(popFirst(rectQueue));
    if (segmenterStream.hasNext()) {
      Segmenter seg = segmenterStream.next();
      if (seg == null) true;
      L<Rect> rects = seg.get(inputImage);
      addAll(rectQueue, rects);
      if (verbose) print("Segmenter " + seg + " returned: " + rects);
      true;
    }
    false;
  }
  
  // returns true if rect not seen before
  bool tryRect(Rect r) {
    r = rectSetHeightToWidth(r); // square it
    if (!rectsTried.add(r)) false; // seen
    BufferedImage board = clipBufferedImage(inputImage, r);
    S fen, double score = unpair chessOCR_recognizeBoard_FENAndScore(board, pieceRecognizer);
    if (verbose) print("Score " + score + " for rect: " + r);
    best.put(pair(r, fen), score);
    true;
  }
  
  void verbose(bool verbose) {
    best.verboseNewBest = this.verbose = verbose;
  }
  
  Rect bestBoardLocation() { ret pairA(best!); }
  Pair<Rect, Double> boardLocationAndScore() { ret pair(pairA(best!), score()); }
}