// Licensed under the Apache License, Version 2.0
// © mihakralj
//@version=6
indicator("Normalized Average True Range", "NATR", overlay=false, format=format.percent, precision=2)

//@function Calculates the Normalized Average True Range (NATR)
//@param length The period length for the ATR calculation.
//@returns The NATR value as a percentage of close price.
//@optimized Beta precomputation for RMA warmup compensation
natr(simple int length) =>
    float prevClose = nz(close[1], close)
    float tr1 = high - low
    float tr2 = math.abs(high - prevClose)
    float tr3 = math.abs(low - prevClose)
    float trueRange = math.max(tr1, math.max(tr2, tr3))
    float alpha = 1.0 / float(length)
    float beta = 1.0 - alpha
    var float EPSILON = 1e-10
    var float raw_rma = 0.0
    var float e = 1.0
    float atrValue = na
    if not na(trueRange)
        raw_rma := (raw_rma * (length - 1) + trueRange) / length
        e *= beta
        atrValue := e > EPSILON ? raw_rma / (1.0 - e) : raw_rma
    float natrValue = close != 0 ? (atrValue / close) * 100 : 0
    natrValue

// ---------- Main loop ----------

// Inputs
i_length = input.int(14, "Length", minval=1, tooltip="Number of bars used for the ATR calculation")

// Calculation
natrValue = natr(i_length)

// Plot
plot(natrValue, "NATR", color=color.yellow, linewidth=2)