Decay Min-Max Channel

// Licensed under the Apache License, Version 2.0
// © mihakralj
//@version=6
indicator("Decay Min-Max Channel (DECAYCHANNEL)", "DECAYCHANNEL", overlay=true)

//@function Calculates the Decaying Min-Max Channel with decay towards midpoint
//@param period Lookback period (period > 0)
//@param hi Source series for the highest high calculation (usually high)
//@param lo Source series for the lowest low calculation (usually low)
//@returns Tuple containing [decaying_highest_high, decaying_lowest_low]
//@optimized Uses exponential decay with O(n) complexity per bar
decaychannel(simple int period, series float hi = high, series float lo = low) =>
    if period <= 0
        runtime.error("Period must be > 0")
    float decayLambda = math.log(2.0) / period
    var float[] hbuf = array.new_float(period, na)
    var float[] lbuf = array.new_float(period, na)
    var float currentMax = na
    var float currentMin = na
    var int timeSinceNewMax = 0
    var int timeSinceNewMin = 0
    int idx = bar_index % period
    array.set(hbuf, idx, hi)
    array.set(lbuf, idx, lo)
    float periodMax = na
    float periodMin = na
    float periodSum = 0.0
    int validCount = 0
    for i = 0 to period - 1
        float hVal = array.get(hbuf, i)
        float lVal = array.get(lbuf, i)
        if not na(hVal) and not na(lVal)
            periodMax := na(periodMax) ? hVal : math.max(periodMax, hVal)
            periodMin := na(periodMin) ? lVal : math.min(periodMin, lVal)
            periodSum := periodSum + (hVal + lVal) / 2.0
            validCount := validCount + 1
    float periodAverage = validCount > 0 ? periodSum / validCount : (hi + lo) / 2.0
    if na(currentMax) or na(currentMin)
        currentMax := na(periodMax) ? hi : periodMax
        currentMin := na(periodMin) ? lo : periodMin
        timeSinceNewMax := 0
        timeSinceNewMin := 0
    else
        if hi >= currentMax
            currentMax := hi
            timeSinceNewMax := 0
        else
            timeSinceNewMax := timeSinceNewMax + 1
        if lo <= currentMin
            currentMin := lo
            timeSinceNewMin := 0
        else
            timeSinceNewMin := timeSinceNewMin + 1
        if validCount > 0
            float midpoint = (currentMax + currentMin) / 2.0
            float maxDecayRate = 1 - math.exp(-decayLambda * timeSinceNewMax)
            float minDecayRate = 1 - math.exp(-decayLambda * timeSinceNewMin)
            currentMax := currentMax - maxDecayRate * (currentMax - midpoint)
            currentMin := currentMin - minDecayRate * (currentMin - midpoint)
            if not na(periodMax)
                currentMax := math.min(currentMax, periodMax)
            if not na(periodMin)
                currentMin := math.max(currentMin, periodMin)
    [currentMax, currentMin]

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

// Inputs
i_period = input.int(100, "Period", minval=1)

// Calculation
[highest, lowest] = decaychannel(i_period)

// Plot
p1 = plot(highest, "Decaying High", color=color.yellow, linewidth=2)
p2 = plot(lowest, "Decaying Low", color=color.yellow, linewidth=2)
fill(p1, p2, color=color.new(color.blue, 90), title="Channel Fill")