// Licensed under the Apache License, Version 2.0
// © mihakralj
//@version=6
indicator("Bessel-Weighted Moving Average (BWMA)", "BWMA", overlay=true)

//@function Calculates BWMA using Bessel window weighting
//@param source Series to calculate BWMA from
//@param period Lookback period - FIR window size
//@param order Bessel function order (default: 0)
//@returns BWMA value, calculates from first bar using available data
//@optimized Uses Bessel window coefficients with O(n) complexity per bar due to lookback loop
bwma(series float source, simple int period, simple int order=0) =>
    if period <= 0
        runtime.error("Period must be greater than 0")
    if order < 0
        runtime.error("Bessel order must be non-negative")
    int p = math.min(bar_index + 1, period)
    var array<float> weights = array.new_float(1, 1.0)
    var int last_p = 1
    var int last_order = order
    if last_p != p or last_order != order
        weights := array.new_float(p, 0.0)
        float total_weight = 0.0
        float scale = 2.0 / (p - 1)
        float power = order / 2.0 + 0.5
        for i = 0 to p - 1
            float x = i * scale - 1.0
            float arg = 1.0 - x * x
            float w = 0.0
            if arg > 0.0
                if order == 0
                    w := arg
                else if order == 1
                    w := arg * math.sqrt(arg)
                else
                    w := math.pow(arg, power)
            array.set(weights, i, w)
            total_weight += w
        if total_weight > 0.0
            float inv_total = 1.0 / total_weight
            for i = 0 to p - 1
                array.set(weights, i, array.get(weights, i) * inv_total)
        last_p := p
        last_order := order
    float sum = 0.0
    float weight_sum = 0.0
    for i = 0 to p - 1
        float price = source[i]
        if not na(price)
            float w = array.get(weights, i)
            sum += price * w
            weight_sum += w
    nz(sum / weight_sum, source)

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

// Inputs
i_period = input.int(10, "Period", minval=1)
i_order = input.int(0, "Bessel Order", minval=0, maxval=3, tooltip="Order of the Bessel function (0-3)")
i_source = input.source(close, "Source")

// Calculation
bwma_value = bwma(i_source, i_period, i_order)

// Plot
plot(bwma_value, "BWMA", color=color.yellow, linewidth=2)