persistable sclass ATR extends CandleBasedIndicator<Double> {
  // For first phase
  new Average initialAverage;
  
  // For second phase
  settable SmoothedMovingAverage sma;
  
  // TR value
  settable double tr = Double.NaN;

  // ATR value
  settable double atr = Double.NaN;
  
  // ATR values collected as ticker
  gettable TickerSequence atrHistory = new TickerSequence("ATR");

  Double value() { ret atr(); }
  
  *(int *length) {}

  {
    length = 14;
    onCandleAdded((IVF1<TradingCandle>) candle -> {
      var x = candle.move();
      var u = max(x, 0.0);
      var d = neg(min(x, 0.0));
      
      // Calculate TR
      if (candles().size() < 2) ret;
      
      tr(trueRange(ll(candles().nextToLast(), candles().last())));
      
      if (initialAverage.count() < length())
        ret with initialAverage.add(tr);
        
      if (sma == null) {
        sma(new SmoothedMovingAverage(length()));
        sma().add(initialAverage!);
      } else
        sma().add(tr);

      atr(sma()!);
      long time = candle.endTime().toLong();
      atrHistory?.addIfPriceChanged(atr, time);
    });
  }
  
  TickerSequence asTicker(L<TradingCandle> candles) {
    feed(candles);
    ret atrHistory;
  }
  
  void reset :: after {
    resetFields(this, "initialAverage sma tr atr atrHistory");
  }
}

Began life as a copy of #1036452