package indicators

// RSI calcule le Relative Strength Index (Wilder's smoothing, période 14).
// Retourne NaN si pas assez de données.
func RSI(closes []float64, period int) float64 {
	if period <= 0 {
		period = 14
	}
	if len(closes) < period+1 {
		return -1
	}

	var gains, losses float64
	for i := 1; i <= period; i++ {
		delta := closes[i] - closes[i-1]
		if delta > 0 {
			gains += delta
		} else {
			losses -= delta
		}
	}

	avgGain := gains / float64(period)
	avgLoss := losses / float64(period)

	// Wilder's smoothing pour le reste
	for i := period + 1; i < len(closes); i++ {
		delta := closes[i] - closes[i-1]
		if delta > 0 {
			avgGain = (avgGain*float64(period-1) + delta) / float64(period)
			avgLoss = (avgLoss * float64(period-1)) / float64(period)
		} else {
			avgGain = (avgGain * float64(period-1)) / float64(period)
			avgLoss = (avgLoss*float64(period-1) - delta) / float64(period)
		}
	}

	if avgLoss == 0 {
		return 100
	}
	rs := avgGain / avgLoss
	return 100 - (100 / (1 + rs))
}