// The MIT License (MIT)
// © mihakralj
//@version=6
indicator("Average True Range Percent (ATRP)", "ATRP", overlay=false, format=format.percent, precision=2)

//@function Calculates the Average True Range Percent (ATRP)
//@param length The period length for the ATR calculation.
//@returns The ATRP value.
//@optimized Beta precomputation for RMA warmup compensation
atrp(simple int length) =>
    if length <= 0
        runtime.error("Period must be greater than 0")
    var float prevClose = close
    float tr1 = high - low
    float tr2 = math.abs(high - prevClose)
    float tr3 = math.abs(low - prevClose)
    float trueRange = math.max(tr1, tr2, tr3)
    prevClose := close
    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 atr = na
    if not na(trueRange)
        raw_rma := (raw_rma * (length - 1) + trueRange) / length
        e *= beta
        atr := e > EPSILON ? raw_rma / (1.0 - e) : raw_rma
    close != 0.0 ? atr / close * 100 : na

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

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

// Calculation
atrpValue = atrp(i_length)

// Plot
plot(atrpValue, "ATRP", color=color.yellow, linewidth=2)