Average Directional Movement Index (ADX)

// Licensed under the Apache License, Version 2.0
// © mihakralj
//@version=6
indicator("Average Directional Movement Index (ADX)", "ADX", overlay=false)

//@function Calculates ADX using Wilder's smoothing with compensated RMA
//@param period Number of bars used in the calculation
//@returns tuple of ADX value, +DI, -DI
adx(simple int period = 14) =>
    if period <= 0
        runtime.error("Period must be greater than 0")
    float tr = na(close[1]) ? high - low : math.max(high - low, math.max(math.abs(high - close[1]), math.abs(low - close[1])))
    float plus_dm = na(high[1]) ? 0.0 : high - high[1] > low[1] - low and high - high[1] > 0 ? high - high[1] : 0.0
    float minus_dm = na(low[1]) ? 0.0 : low[1] - low > high - high[1] and low[1] - low > 0 ? low[1] - low : 0.0
    var float tr_sum = 0.0
    var float plus_dm_sum = 0.0
    var float minus_dm_sum = 0.0

    tr_sum := nz(tr_sum) - nz(tr_sum[period]) + tr
    plus_dm_sum := nz(plus_dm_sum) - nz(plus_dm_sum[period]) + plus_dm
    minus_dm_sum := nz(minus_dm_sum) - nz(minus_dm_sum[period]) + minus_dm

    float plus_di = tr_sum != 0.0 ? math.min(100 * plus_dm_sum / tr_sum, 50.0) : 0.0
    float minus_di = tr_sum != 0.0 ? math.min(100 * minus_dm_sum / tr_sum, 50.0) : 0.0
    float dx = plus_di + minus_di != 0.0 ? 100 * math.abs(plus_di - minus_di) / (plus_di + minus_di) : 0.0

    var float dx_sum = 0.0
    dx_sum := nz(dx_sum) - nz(dx_sum[period]) + dx
    float adx_value = dx_sum / period
    [adx_value, plus_di, minus_di]

// Inputs
i_period = input.int(14, "Period", minval=1, tooltip="Number of bars used in the calculation")

// Calculate ADX
[adx_value, plus_di, minus_di] = adx(i_period)

// Plot
plot(adx_value, "ADX", color=color.yellow, linewidth=2)
plot(plus_di, "+DI", color=color.yellow, linewidth=2)
plot(minus_di, "-DI", color=color.yellow, linewidth=2)