// Licensed under the Apache License, Version 2.0
// © mihakralj
//@version=6
indicator("Weighted Mean Absolute Percentage Error", "WMAPE", overlay=false, format=format.percent)

//@function Calculates Weighted Mean Absolute Percentage Error
//@param   actual Series of actual values
//@param   predicted Series of predicted/forecast values
//@param   length Rolling window for calculation
//@returns WMAPE value as percentage
wmape(series float actual, series float predicted, simple int length) =>
    float epsilon = 1e-10

    // Compute absolute error and absolute actual for current bar
    float absError = math.abs(nz(actual, 0.0) - nz(predicted, 0.0))
    float absActual = math.abs(nz(actual, 0.0))

    // Rolling sums
    float sumAbsError = ta.sum(absError, length)
    float sumAbsActual = ta.sum(absActual, length)

    // WMAPE = (Σ|error| / Σ|actual|) * 100
    float result = sumAbsActual > epsilon ? (sumAbsError / sumAbsActual) * 100.0 : 0.0
    result

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

// Inputs
i_length = input.int(14, "Length", minval=1)
i_actual = input.source(close, "Actual")
i_predicted = input.source(open, "Predicted")

// Calculation
wmape_value = wmape(i_actual, i_predicted, i_length)

// Plot
plot(wmape_value, "WMAPE", color=color.yellow, linewidth=2)
hline(0, "Perfect", color=color.green, linestyle=hline.style_dotted)