// Licensed under the Apache License, Version 2.0
// © mihakralj
//@version=6
indicator("Entropy (ENTROPY)", "ENTROPY", overlay=false)

 //@function Calculate normalized Shannon entropy of a series over a lookback period.
 //@param source series<float> Input data series. NA values are ignored.
 //@param length int Lookback period (>= 1).
 //@returns series<float> Normalized entropy value [0, 1], or na if insufficient data.
 //@optimized for performance and dirty data
entropy(source, length) =>
    if length < 1
        runtime.error("Length must be >= 1")
    var float validMin = na
    var float validMax = na
    var int validCount = 0
    for i = 0 to length - 1
        val = source[i]
        if not na(val)
            if na(validMin)
                validMin := val
                validMax := val
            else
                validMin := math.min(validMin, val)
                validMax := math.max(validMax, val)
            validCount += 1
    var float normalizedEntropy = na
    if validCount < 2
        normalizedEntropy := na
    else
        valueRange = validMax - validMin
        if valueRange <= 1e-10
            normalizedEntropy := 0.0
        else
            bins = math.min(math.max(validCount, 2), 100)
            int[] freq = array.new_int(bins, 0)
            float sumOfValidPoints = 0.0
            for i = 0 to length - 1
                val = source[i]
                if not na(val)
                    normVal = (val - validMin) / valueRange
                    bucket = math.floor(math.min(math.max(normVal, 0.0), 1.0 - 1e-10) * bins)
                    safeBucket = math.max(0, math.min(bucket, bins - 1))
                    array.set(freq, safeBucket, array.get(freq, safeBucket) + 1)
                    sumOfValidPoints += 1
            float entropySumComponent = 0.0
            if sumOfValidPoints > 0
                for i = 0 to bins - 1
                    count = array.get(freq, i)
                    if count > 0
                        p = count / sumOfValidPoints
                        entropySumComponent += -p * math.log(p)
                maxEntropy = math.log(bins)
                normalizedEntropy := maxEntropy > 1e-10 ? entropySumComponent / maxEntropy : 0.0
    normalizedEntropy

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

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

// Calculation
entropyValue = entropy(i_source, i_length)

// Plot
plot(entropyValue, "Entropy", color=color.blue, color=color.yellow, linewidth=2)