Bollinger Band Mean Reversion

//@version=5
strategy("Bollinger Band Mean Reversion", overlay=true, initial_capital=10000, default_qty_type=strategy.percent_of_equity, default_qty_value=100, commission_type=strategy.commission.percent, commission_value=0.1)

// === INPUTS ===
bbLength = input.int(20, "Bollinger Band Period", minval=5, maxval=200)
bbMult = input.float(2.0, "Bollinger Band StdDev", minval=0.5, maxval=4.0, step=0.1)
atrLength = input.int(14, "ATR Period for Stop", minval=5, maxval=50)
atrMultiplier = input.float(1.5, "ATR Stop Multiplier", minval=0.5, maxval=5.0, step=0.1)

// === INDICATORS ===
[bbMiddle, bbUpper, bbLower] = ta.bb(close, bbLength, bbMult)
atrValue = ta.atr(atrLength)

// === SIGNALS ===
// Long: price touches or crosses below lower band
longCondition = ta.crossunder(close, bbLower)
// Close long: price reaches middle band
closeLongCondition = ta.crossover(close, bbMiddle)

// Short: price touches or crosses above upper band
shortCondition = ta.crossover(close, bbUpper)
// Close short: price reaches middle band
closeShortCondition = ta.crossunder(close, bbMiddle)

// === EXECUTION ===
if longCondition
    strategy.entry("Long", strategy.long)

if closeLongCondition
    strategy.close("Long")

if shortCondition
    strategy.entry("Short", strategy.short)

if closeShortCondition
    strategy.close("Short")

// ATR-based stop loss
if strategy.position_size > 0
    longStop = strategy.position_avg_price - atrValue * atrMultiplier
    strategy.exit("Long SL", "Long", stop=longStop)

if strategy.position_size < 0
    shortStop = strategy.position_avg_price + atrValue * atrMultiplier
    strategy.exit("Short SL", "Short", stop=shortStop)

// === PLOTTING ===
plot(bbMiddle, "BB Middle", color=color.yellow, linewidth=1)
plot(bbUpper, "BB Upper", color=color.red, linewidth=1)
plot(bbLower, "BB Lower", color=color.green, linewidth=1)
fill(plot(bbUpper, display=display.none), plot(bbLower, display=display.none), color=color.new(color.gray, 90))