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

//@function Calculates Mean Arctangent Absolute Percentage Error
//@param   actual Series of actual values
//@param   predicted Series of predicted/forecast values
//@param   length Rolling window for averaging
//@returns MAAPE value (0 to ~1.5708)
maape(series float actual, series float predicted, simple int length) =>
    float epsilon = 1e-10

    // Compute arctangent percentage error for current bar
    float absActual = math.abs(nz(actual, 0.0))
    float absError = math.abs(nz(actual, 0.0) - nz(predicted, 0.0))
    float atanError = absActual > epsilon ? math.atan(absError / absActual) : math.pi / 2.0

    // Rolling mean of arctangent errors
    float result = ta.sma(atanError, length)
    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
maape_value = maape(i_actual, i_predicted, i_length)

// Plot
plot(maape_value, "MAAPE", color=color.yellow, linewidth=2)
hline(0, "Zero", color=color.gray, linestyle=hline.style_dotted)
hline(math.pi / 2.0, "Max (π/2)", color=color.red, linestyle=hline.style_dotted)