// The MIT License (MIT)
// © mihakralj
//@version=6
indicator("Super Trend Bands (STBANDS)", "STBANDS", overlay=true)

//@function Calculates Super Trend Bands using ATR-based dynamic support/resistance
//@param source Series to calculate bands from
//@param period Lookback period for ATR calculation
//@param multiplier ATR multiplier for band distance
//@returns [upper_band, lower_band, trend] Super Trend band values and trend direction
//@optimized for performance and dirty data
stbands(series float source, simple int period, simple float multiplier) =>
    if period <= 0 or multiplier <= 0.0
        runtime.error("Period and multiplier must be greater than 0")
    var int p = math.max(1, period), var int head = 0, var int count = 0
    var array<float> tr_buffer = array.new_float(p, na)
    var float tr_sum = 0.0
    float high_val = nz(high), float low_val = nz(low), float close_val = nz(source)
    float prev_close = nz(source[1], source)
    float tr = math.max(high_val - low_val, math.max(math.abs(high_val - prev_close), math.abs(low_val - prev_close)))
    float oldest_tr = array.get(tr_buffer, head)
    if not na(oldest_tr)
        tr_sum -= oldest_tr
        count -= 1
    tr_sum += tr
    count += 1
    array.set(tr_buffer, head, tr)
    head := (head + 1) % p
    float atr = count > 0 ? tr_sum / count : tr
    float hl2_val = (high_val + low_val) / 2
    float basic_upper = hl2_val + multiplier * atr
    float basic_lower = hl2_val - multiplier * atr
    var float final_upper = na, var float final_lower = na
    var int trend = 1
    
    // Initialize on first bar
    if bar_index == 0
        final_upper := basic_upper
        final_lower := basic_lower
        trend := 1
    else
        prev_upper = nz(final_upper[1], basic_upper)
        prev_lower = nz(final_lower[1], basic_lower)
        prev_close_val = nz(source[1], source)
        
        final_upper := basic_upper < prev_upper or prev_close_val > prev_upper ? basic_upper : prev_upper
        final_lower := basic_lower > prev_lower or prev_close_val < prev_lower ? basic_lower : prev_lower
        
        prev_trend = nz(trend[1], 1)
        trend := close_val <= prev_lower ? 1 : close_val >= prev_upper ? -1 : prev_trend
    
    [final_upper, final_lower, trend]

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

// Inputs
i_period = input.int(10, "ATR Period", minval=1)
i_source = input.source(close, "Source")
i_multiplier = input.float(3.0, "ATR Multiplier", minval=0.001)

// Calculation
[upper_band, lower_band, trend] = stbands(i_source, i_period, i_multiplier)

// Plot
p_upper = plot(upper_band, "Upper Band", color=color.yellow, linewidth=2)
p_lower = plot(lower_band, "Lower Band", color=color.yellow, linewidth=2)
fill(p_upper, p_lower, color=color.new(color.blue, 90), title="Band Fill")