Mean Deviation

// Licensed under the Apache License, Version 2.0
// © mihakralj
//@version=6
indicator("Mean Deviation (MEANDEV)", "MEANDEV", overlay=false, precision=8)

//@function Calculates the mean absolute deviation from the mean over the specified period.
//@param src {series float} Source series.
//@param len {int} Lookback length. `len` > 0.
//@returns {series float} Mean deviation of `src` for `len` bars back. Returns 0 if not enough data.
meandev(series float src, int len) =>
    if len <= 0
        runtime.error("Period must be greater than 0")
    var int p = math.max(1, len)
    var array<float> buffer = array.new_float(p, na)
    var int head = 0, var int count = 0
    var float sum = 0.0

    // Update circular buffer and running sum
    float oldest = array.get(buffer, head)
    if not na(oldest)
        sum -= oldest
        count -= 1
    float val = nz(src)
    sum += val
    count += 1
    array.set(buffer, head, val)
    head := (head + 1) % p

    if count < 1
        0.0
    else
        // Calculate mean
        float mean = sum / count

        // Calculate mean absolute deviation
        float devSum = 0.0
        int start = count < p ? 0 : head
        for i = 0 to count - 1
            int idx = (start + i) % p
            float v = array.get(buffer, idx)
            if not na(v)
                devSum += math.abs(v - mean)

        devSum / count


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

// Inputs
i_period = input.int(14, "Period", minval=1)
i_source = input.source(close, "Source")

// Calculation
meandev_value = meandev(i_source, i_period)

// Plot
plot(meandev_value, "MeanDev", color=color.yellow, linewidth=2)