// Licensed under the Apache License, Version 2.0
// © mihakralj
//@version=6
indicator("Geometric Mean (GEOMEAN)", "GEOMEAN", overlay=true)

//@function Calculates the Geometric Mean of a series over a lookback period.
//@param src series float Input data series (must contain positive values).
//@param len simple int Lookback period (must be > 0).
//@returns series float The Geometric Mean, or na if data is not suitable (e.g., non-positive values, insufficient data).
//@optimized for performance and dirty data
geomean(series float src, simple int len) =>
    if len <= 0
        runtime.error("Period must be greater than 0. Found: " + str.tostring(len))
    var float sum_log_src = 0.0
    var int n_valid = 0
    var float[] src_buffer = array.new_float(len, na)
    var int current_index = 0
    float current_val = src
    float current_log_val = na
    bool current_val_is_valid = false
    if not na(current_val) and current_val > 0
        current_log_val := math.log(current_val)
        current_val_is_valid := true
    float old_src_from_buffer = array.get(src_buffer, current_index)
    if not na(old_src_from_buffer) and old_src_from_buffer > 0
        sum_log_src -= math.log(old_src_from_buffer)
        n_valid -= 1
    if current_val_is_valid
        sum_log_src += current_log_val
        n_valid += 1
        array.set(src_buffer, current_index, current_val)
    else
        array.set(src_buffer, current_index, na)
    current_index := (current_index + 1) % len
    if n_valid > 0
        math.exp(sum_log_src / n_valid)
    else
        float(na)

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

// Inputs
i_source = input.source(close, title="Source (must be positive values)")
i_length = input.int(14, title="Lookback Period", minval=1)

// Calculation
geomean_value = geomean(i_source, i_length)

// Plot
plot(geomean_value, "GEOMEAN", color=color.yellow, linewidth=2)