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

//@function Calculates DEM (DeMarker Oscillator)
//@param period SMA lookback period (default 14)
//@returns DEM value in [0, 1] range; 0.3=oversold, 0.7=overbought
//@optimized Uses 2 circular buffers for O(1) per-bar SMA computation
dem(simple int period) =>
    if period <= 0
        runtime.error("Period must be greater than 0")
    if period > 5000
        runtime.error("Period exceeds maximum of 5000")

    float prevHigh = nz(high[1], high)
    float prevLow  = nz(low[1],  low)

    float deMax = math.max(high - prevHigh, 0.0)
    float deMin = math.max(prevLow - low,  0.0)

    var array<float> deMaxBuf = array.new_float(period, 0.0)
    var array<float> deMinBuf = array.new_float(period, 0.0)
    var int idx = 0
    var float deMaxSum = 0.0
    var float deMinSum = 0.0

    deMaxSum -= array.get(deMaxBuf, idx)
    deMinSum -= array.get(deMinBuf, idx)

    array.set(deMaxBuf, idx, deMax)
    array.set(deMinBuf, idx, deMin)

    deMaxSum += deMax
    deMinSum += deMin

    idx := (idx + 1) % period

    float denom = deMaxSum + deMinSum
    float result = denom != 0.0 ? deMaxSum / denom : 0.5

    result

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

// Inputs
i_period = input.int(14, "Period", minval=1, maxval=5000, tooltip="SMA smoothing period (traditional: 14)")

// Calculation
dem_value = dem(i_period)

// Plot
plot(dem_value, "DEM", color.new(color.yellow, 0), 2)
hline(0.7, "Overbought",  color=color.red,   linestyle=hline.style_dotted)
hline(0.5, "Midline",     color=color.gray,  linestyle=hline.style_dotted)
hline(0.3, "Oversold",    color=color.green, linestyle=hline.style_dotted)