calculate method

@override IndicatorResult calculate(List<Candle> candles)

Pure computation function that produces an IndicatorResult from candles.

Implementation

@override
IndicatorResult calculate(List<Candle> candles) {
  final n = candles.length;
  final adx = List<double?>.filled(n, null);
  final plusDI = List<double?>.filled(n, null);
  final minusDI = List<double?>.filled(n, null);

  if (n < period + 1) {
    return _result(adx, plusDI, minusDI);
  }

  // Calculate True Range, +DM, -DM
  final tr = List<double>.filled(n, 0);
  final pdm = List<double>.filled(n, 0);
  final mdm = List<double>.filled(n, 0);

  for (int i = 1; i < n; i++) {
    final high = candles[i].high;
    final low = candles[i].low;
    final prevClose = candles[i - 1].close;
    final prevHigh = candles[i - 1].high;
    final prevLow = candles[i - 1].low;

    tr[i] = [high - low, (high - prevClose).abs(), (low - prevClose).abs()].reduce((a, b) => a > b ? a : b);

    final upMove = high - prevHigh;
    final downMove = prevLow - low;
    pdm[i] = (upMove > downMove && upMove > 0) ? upMove : 0;
    mdm[i] = (downMove > upMove && downMove > 0) ? downMove : 0;
  }

  // Smoothed (Wilder's) sums
  double atr = 0, aPdm = 0, aMdm = 0;
  for (int i = 1; i <= period; i++) {
    atr += tr[i]; aPdm += pdm[i]; aMdm += mdm[i];
  }

  double adxSum = 0;
  int adxCount = 0;

  for (int i = period; i < n; i++) {
    if (i > period) {
      atr = atr - (atr / period) + tr[i];
      aPdm = aPdm - (aPdm / period) + pdm[i];
      aMdm = aMdm - (aMdm / period) + mdm[i];
    }

    final pdi = atr > 0 ? (100.0 * aPdm / atr) : 0.0;
    final mdi = atr > 0 ? (100.0 * aMdm / atr) : 0.0;
    plusDI[i] = pdi;
    minusDI[i] = mdi;

    final diSum = pdi + mdi;
    final dx = diSum > 0 ? (100.0 * (pdi - mdi).abs() / diSum) : 0.0;

    adxSum += dx;
    adxCount++;
    if (adxCount >= period) {
      adx[i] = adxCount == period
          ? adxSum / period
          : ((adx[i - 1] ?? 0) * (period - 1) + dx) / period;
    }
  }

  return _result(adx, plusDI, minusDI);
}