// Licensed under the Apache License, Version 2.0
// © mihakralj
//@version=6
indicator("Triple Exponential Average (TRIX)", "TRIX", overlay=false)

//@function Calculates TRIX oscillator with compensation
//@param source Series to calculate TRIX from
//@param period Period for triple exponential smoothing
//@returns TRIX value (percentage rate of change of triple EMA)
trix(series float source, simple int period) =>
    if period <= 0
        runtime.error("Period must be positive")
    float src = na(source) ? source[1] : source
    float alpha = 2.0 / (period + 1)
    float d = 1 - alpha
    var float e1 = 1.0, var float e2 = 1.0, var float e3 = 1.0
    var bool warmup = true
    var float rema1 = 0, var float rema2 = 0, var float rema3 = 0
    var float ema1 = src, var float ema2 = src, var float ema3 = src
    var float prev_ema3 = src
    rema1 := alpha * (src - rema1) + rema1
    if warmup
        e1 *= d, e2 *= d, e3 *= d
        ema1 := rema1 / (1.0 - e1)
        rema2 := alpha * (ema1 - rema2) + rema2
        ema2 := rema2 / (1.0 - e2)
        rema3 := alpha * (ema2 - rema3) + rema3
        ema3 := rema3 / (1.0 - e3)
        warmup := e1 > 1e-10
    else
        ema1 := rema1
        rema2 := alpha * (ema1 - rema2) + rema2
        ema2 := rema2
        rema3 := alpha * (ema2 - rema3) + rema3
        ema3 := rema3
    trix_value = prev_ema3 != 0 ? 100 * (ema3 - prev_ema3) / prev_ema3 : 0
    prev_ema3 := ema3
    na(source) ? na : trix_value

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

// Inputs
i_period = input.int(14, "Period", minval=1, maxval=100, tooltip="Period for triple exponential smoothing")
i_source = input.source(close, "Source", tooltip="Price series to analyze")

// Calculation
trix_value = trix(i_source, i_period)

// Plot
plot(trix_value, "TRIX", color=color.yellow, linewidth=2)