srecord noeq G22_RegionToSSIs_v2(IImageRegion region) extends Meta {

  RGB color;

  L<SSI> ssis;

  new L<GrowingSSI> growingSSIs;

  settable bool withDiagonals;

  settable bool checkCoherence = true;

  settable bool checkStreaks = true;

  private int x1, y;

  class GrowingSSI {

    settable int y1;

    new ShortBuffer data;

    int y2() { ret y1+l(data)/2; }

    SSI finish() {

      ret addAndReturn(ssis, new SSI(y1, y2()).data(data.toArray())

        .color(color));

    }

    bool isEmpty() { ret data.isEmpty(); }

    int lastx1() { ret data.get(l(data)-2); }

    int lastx2() { ret data.get(l(data)-1); }

    IntRange lastRange() { ret isEmpty() ? null : intRange(lastx1(), lastx2()); }

    void add(int x1, int x2) {

      if (checkCoherence() && !isEmpty()

        && !intRangesOverlap(x1, x2, lastx1()-diag(), lastx2()+diag()))

        fail("Coherence fail", +lastx1(), +lastx2(), +x1, +x2);

      data.add(toShort_enforce(x1));

      data.add(toShort_enforce(x2));

    }

  }

  void finishSSI(int iSSI) {

    growingSSIs.remove(iSSI).finish();

  }

  private GrowingSSI startSSI(int iSSI default l(growingSSIs), IntRange range) {

    if (scaffoldingEnabled()) printVars("startSSI", +iSSI, +range);

    var ssi = new GrowingSSI().y1(y);

    ssi.add(range.start, range.end);

    ret addAndReturn(growingSSIs, iSSI, ssi);

  }

  L<IntRange> lastStreaks() {

    ret reallyLazyMap(growingSSIs, -> .lastRange());

  }

  int diag() { ret withDiagonals ? 1 : 0; }

  L<SSI> get() {

    if (region == null) null;

    color = region.color();

    ssis = new L;

    Rect r = region.bounds();

    int x1 = this.x1 = r.x1(), y1 = r.y1(), y2 = r.y2(), h = y2-y1, w = r.w;

    bool scaff = scaffoldingEnabled();

    for (y = y1; y < y2; y++) {

      reMutable y;

      L<IntRange> streaks = shiftIntRanges(x1, genericStreaks(w, x -> region.contains(x1+x, y)));

      var lastStreaks = lastStreaks();

      if (checkStreaks())

        assertProperStreaks(lastStreaks);

      // advance iSSI & iStreak simultaneously

      int iStreak = 0, iSSI = 0;

      int nStreaks = l(streaks);

      if (scaff) printVars(+y, +lastStreaks, +streaks);

      while ping (iStreak < nStreaks) {

        var range = streaks.get(iStreak);

        var ssi = _get(growingSSIs, iSSI);

        if (scaff) printVars(+y, +iStreak, +iSSI, +range, ssi := ssi?.lastRange());

        // case 1:

        //           ------

        // -------

        //

        // case 2:

        //

        // -------

        // (left of current SSI or to the right of everything)

        if (ssi == null || range.end <= ssi.lastx1()-diag()) {

          startSSI(iSSI++, range);

          ++iStreak;

          continue;

        }

        // Now we know that we have another SSI.

        // case 3:

        // -------

        //          ------

        // (Just end current SSI and do streak again.)

        if (range.start >= ssi.lastx2()+diag()) {

          finishSSI(iSSI);

          continue;

        }

        // Find the rightmost streak still under the current SSI

        int jStreak = iStreak+1;

        while (jStreak < nStreaks && streaks.get(jStreak).start < ssi.lastx2()+diag())

          ++jStreak;

        range = streaks.get(jStreak-1);

        // Check if we have to merge with right neighbor(s)

        int jSSI = iSSI+1;

        while (jSSI < l(growingSSIs)

          && range.end > growingSSIs.get(jSSI).lastx1()-diag())

          ++jSSI;

        int nSSI = jSSI-iSSI, nStreak = jStreak-iStreak;

        if (scaff) printVars(+jStreak, +jSSI, +nSSI, +nStreak, +nStreaks, nSSIs := l(growingSSIs));

        if (scaff) printVars(+nSSI, +nStreak);

        // Now we go from [iSSI;jSSI) to [iStreak;jStreak)

        // The only case without structural changes is when

        // nSSI = nStreak = 1. Then we just add the line.

        if (nSSI == 1 && nStreak == 1) {

          ssi.add(range.start, range.end);

          iSSI = jSSI; iStreak = jStreak; continue;

        }

        // If 2 -> 2, we can just assign them one-to-one I think

        if (nSSI == 2 && nStreak == 2) {

          if (scaff) printVars("2->2", ssis := subList(lastStreaks(), iSSI, jSSI),

            streaks := subList(streaks, iStreak, jStreak));

          while (iSSI < jSSI) {

            range = streaks.get(iStreak++);

            growingSSIs.get(iSSI++).add(range.start, range.end);

          }

          continue;

        }

        if (nSSI > 1 && nStreak > 1)

          printVars("ANOMALY", +nSSI, +nStreak,

            ssis := subList(lastStreaks(), iSSI, jSSI),

            streaks := subList(streaks, iStreak, jStreak));

        // Any kind of structural change means end all involved

        // SSIs and start new ones.

        while (jSSI-- > iSSI)

          finishSSI(iSSI);

        while (iStreak < jStreak)

          startSSI(iSSI++, streaks.get(iStreak++));

      }

      // end SSIs to the right of all streaks

      while (iSSI < l(growingSSIs))

        finishSSI(iSSI);

    }

    for (ssi : cloneAndClear(growingSSIs)) ssi.finish();

    ret ssis;

  }

}