sclass BollingerBands extends CandleBasedIndicator<DoubleRange> {

  replace Candle with TradingCandle.

  // length parameter is in base class

  // The magic average + standard deviation generator

  new Welford welford;

  // Probably wrong word. Defines how many times the standard deviation

  // we use as the tunnel size (well, twice that, actually)

  settable double deviation = 2;

  // result

  settable DoubleRange range;

  // Bands collected as tickers

  gettable TickerSequence upperBand = new TickerSequence("Upper Bollinger Band");

  gettable TickerSequence lowerBand = new TickerSequence("Lower Bollinger Band");

  gettable AverageAndStandardDeviation as;

  {

    onCandleRemoved(candle -> welford.remove(candle.endPrice()));

    onCandleAdded(candle -> {

      welford.add(candle.endPrice());

      if (l(candles()) >= length) {

        var bCandles = candles().asList();

        //var prices = mapToDoubleArray(bCandles, ->.endPrice());

        //as = averageAndStandardDeviation(prices);

        as = welford!;

        range(bollingerRange(as, deviation));

        upperBand?.addIfPriceChanged(range.end(), candle.endTime().toLong());

        lowerBand?.addIfPriceChanged(range.start(), candle.endTime().toLong());

        change();

      }

    });

  }

  L<TickerSequence> bandsAsTickers(L<TradingCandle> candles) {

    feed(candles);

    ret ll(upperBand, lowerBand);

  }

  DoubleRange value() { ret range(); }

  void reset :: after {

    resetFields(this, "welford range upperBand lowerBand as");

  }

}