//@version=5
strategy("Cross-Exchange Statistical Arbitrage Strategy", overlay=false, initial_capital=10000, default_qty_type=strategy.percent_of_equity, default_qty_value=100)

// Inputs
secondarySymbol = input.symbol("BINANCE:BTCUSDT", "Secondary Reference Symbol")
lookback        = input.int(20, "Lookback Period for Z-Score", minval=5)
threshold       = input.float(2.0, "Z-Score Entry Threshold", minval=0.5, step=0.1)
exitThreshold   = input.float(0.0, "Z-Score Exit Threshold", step=0.1)

// Fetch secondary asset close price
pricePrimary   = close
priceSecondary = request.security(secondarySymbol, timeframe.period, close)

// Calculate Spread & Z-Score
spread    = pricePrimary - priceSecondary
spreadSMA = ta.sma(spread, lookback)
spreadStd = ta.stdev(spread, lookback)
zScore    = spreadStd != 0.0 ? (spread - spreadSMA) / spreadStd : 0.0

// Plots
plot(zScore, "Spread Z-Score", color=color.blue)
hline(threshold, "Upper Threshold", color=color.red, linestyle=hline.style_dashed)
hline(-threshold, "Lower Threshold", color=color.green, linestyle=hline.style_dashed)
hline(exitThreshold, "Mean Reversion Level", color=color.gray, linestyle=hline.style_dotted)

// Trading Conditions
longCondition  = ta.crossover(zScore, -threshold)
shortCondition = ta.crossunder(zScore, threshold)

exitLongCondition  = zScore >= exitThreshold
exitShortCondition = zScore <= exitThreshold

// Strategy Execution
if (longCondition)
    strategy.entry("Arb_Long", strategy.long)

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

if (strategy.position_size > 0 and exitLongCondition)
    strategy.close("Arb_Long")

if (strategy.position_size < 0 and exitShortCondition)
    strategy.close("Arb_Short")