Mean Reversion Strategy Based on ATR

/*backtest
start: 2022-10-16 00:00:00
end: 2023-10-16 00:00:00
period: 1d
basePeriod: 1h
exchanges: [{"eid":"Futures_Binance","currency":"BTC_USDT"}]
*/

// This source code is subject to the terms of the Mozilla Public License 2.0 at https://mozilla.org/MPL/2.0/
// © DojiEmoji

//@version=5
strategy("Mean Reversion (ATR) Strategy v2 [KL] ", overlay=true, pyramiding=1)
var string ENUM_LONG = "Long"
var string GROUP_TEST = "Hypothesis testing"
var string GROUP_TSL = "Stop loss"
var string GROUP_TREND = "Trend prediction"

backtest_timeframe_start = input(defval=timestamp("01 Apr 2000 13:30 +0000"), title="Backtest Start Time")
within_timeframe = true

// TSL: calculate the stop loss price. {
ATR_TSL      = ta.atr(input(14, title="Length of ATR for trailing stop loss", group=GROUP_TSL)) * input(2.0, title="ATR Multiplier for trailing stop loss", group=GROUP_TSL)
TSL_source      = low
TSL_line_color  = color.green
TSL_transp      = 100
var stop_loss_price = float(0)

if strategy.position_size == 0 or not within_timeframe
    TSL_line_color := color.black
    stop_loss_price := TSL_source - ATR_TSL
else if strategy.position_size > 0
    stop_loss_price := math.max(stop_loss_price, TSL_source - ATR_TSL)
    TSL_transp := 0

plot(stop_loss_price, color=color.new(TSL_line_color, TSL_transp))
// } end of "TSL" block

// Entry variables {
// ATR diversion test via Hypothesis testing (2-tailed):
//     H0 : atr_fast equals atr_slow
//     Ha : reject H0 if z_stat is above critical value, say reliability factor of 1.96 for a 95% confidence interval
len_fast    = input(14,title="Length of ATR (fast) for diversion test", group=GROUP_TEST)
atr_fast    = ta.atr(len_fast)
std_error   = ta.stdev(ta.tr, len_fast) / math.pow(len_fast, 0.5) // Standard Error (SE) = std / sq root(sample size)

atr_slow = ta.atr(input(28,title="Length of ATR (slow) for diversion test", group=GROUP_TEST))
test_stat = (atr_fast - atr_slow) / std_error
reject_H0 = math.abs(test_stat) > input.float(1.645,title="Reliability factor", tooltip="Strategy uses 2-tailed test; Confidence Interval = Point Estimate (avg ATR) +/- Reliability Factor x Standard Error; i.e use 1.645 for a 90% confidence interval", group=GROUP_TEST)

// main entry signal, subject to confirmation(s), gets passed onto the next bar
var _signal_diverted_ATR = false
if not _signal_diverted_ATR
    _signal_diverted_ATR := reject_H0


// confirmation: trend prediction; based on expected lognormal returns
_prcntge_chng = math.log(close / close[1]) 

// Expected return (drift) = average percentage change + half variance over the lookback period
len_drift = input(14, title="Length of drift", group=GROUP_TREND)
_drift = ta.sma(_prcntge_chng, len_drift) - math.pow(ta.stdev(_prcntge_chng, len_drift), 2) * 0.5
_signal_uptrend = _drift > _drift[1]

entry_signal_all = _signal_diverted_ATR and _signal_uptrend // main signal + confirmations
// } end of "Entry variables" block

// MAIN {
// Update the stop limit if strategy holds a position
if strategy.position_size > 0 and ta.change(stop_loss_price)
    strategy.exit(ENUM_LONG, comment="sl", stop=stop_loss_price)

// Entry
if within_timeframe and entry_signal_all
    strategy.entry(ENUM_LONG, strategy.long, comment=strategy.position_size > 0 ? "adding" : "initial")

// Alerts
_atr = ta.atr(14)
alert_helper(msg) =>
    prefix = "[" + syminfo.root + "] "
    suffix = "(P=" + str.tostring(close, "#.##") + "; atr=" + str.tostring(_atr, "#.##") + ")"
    alert(str.tostring(prefix) + str.tostring(msg) + str.tostring(suffix), alert.freq_once_per_bar)

if strategy.position_size > 0 and ta.change(strategy.position_size)
    if strategy.position_size > strategy.position_size[1]
        alert_helper("BUY")
    else if strategy.position_size < strategy.position_size[1]
        alert_helper("SELL")

// Clean up - set the variables back to default values once no longer in use
if strategy.position_size == 0
    stop_loss_price := float(0)
if ta.change(strategy.position_size)
    _signal_diverted_ATR := false
// } end of MAIN block