Aroon Trend Trail [BackQuant] For ThinkOrSwim

[Typegod]

Author states:
Aroon Trend Trail is a trend overlay that uses the relative recency of recent highs and lows to determine direction, then plots an ATR-based trailing rail whose width changes with the strength of the Aroon bias.

The indicator has two separate parts:

• Aroon state: determines whether the trend is bullish or bearish.
• Trend rail: provides a ratcheting lower or upper boundary based on ATR.

The rail itself does not determine trend changes. Bullish and bearish flips come from the Aroon bias crossing the selected Bias Threshold.

original Tradingview script: https://www.tradingview.com/script/30BBpKLx-Aroon-Trend-Trail-BackQuant/

# Aroon Trend Trail [BackQuant]
# Converted to ThinkScript = W. Kalvin

# Aroon Trend Trail is a trend overlay that uses the relative recency of recent highs and lows to determine direction, then plots an ATR-based trailing rail whose width changes with the strength of the Aroon bias.

# The indicator has two separate parts:

# • Aroon state: determines whether the trend is bullish or bearish.
# • Trend rail: provides a ratcheting lower or upper boundary based on ATR.

# The rail itself does not determine trend changes. Bullish and bearish flips come from the Aroon bias crossing the selected Bias Threshold.


# Inputs
input aroonLen = 25;
input flipThreshold = 0.15;
input atrLen = 14;
input atrFactor = 1.8;
input strongWidth = 0.65;
input weakWidth = 1.25;
input breakOnFlip = yes;

input lineW = 3;
input showFill = yes;
input showGlow = yes;
input showAroon = no;
input paintCandles = yes;

# Aroon Calculations using explicit type casting
def sinceHigh = (GetMaxValueOffset(high, aroonLen));
def sinceLow = (GetMinValueOffset(low, aroonLen));

def aroonUp = 100.0 * (aroonLen - AbsValue(sinceHigh)) / aroonLen;
def aroonDown = 100.0 * (aroonLen - AbsValue(sinceLow)) / aroonLen;

def aroonBias = (aroonUp - aroonDown) / 100.0;
def aroonStrength = Min(AbsValue(aroonBias), 1.0);

# Trend State Logic
rec trend = if IsNaN(trend[1]) then (if aroonBias >= 0.0 then 1 else -1)
else if trend[1] == 0 then (if aroonBias >= 0.0 then 1 else -1)
else if trend[1] != 1 and aroonBias > flipThreshold then 1
else if trend[1] != -1 and aroonBias < -flipThreshold then -1
else trend[1];

def bullFlip = (trend == 1) and (trend[1] == -1);
def bearFlip = (trend == -1) and (trend[1] == 1);
def trendFlip = bullFlip or bearFlip;
def isBull = trend == 1;

# Adaptive Rail Width
def atr = WildersAverage(TrueRange(high, close, low), atrLen);
def widthScale = weakWidth + (strongWidth - weakWidth) * aroonStrength;
def railWidth = atr * atrFactor * widthScale;

def rawLower = hl2 - railWidth;
def rawUpper = hl2 + railWidth;

# Ratcheting Rail
rec lowerRail = if IsNaN(lowerRail[1]) then rawLower
else if trend == 1 then (if bullFlip then rawLower else Max(lowerRail[1], rawLower))
else rawLower;

rec upperRail = if IsNaN(upperRail[1]) then rawUpper
else if trend == -1 then (if bearFlip then rawUpper else Min(upperRail[1], rawUpper))
else rawUpper;

def activeRail = if isBull then lowerRail else upperRail;
def plottedRail = if breakOnFlip and trendFlip then Double.NaN else activeRail;

# Plots
plot TrendRail = plottedRail;
TrendRail.SetLineWeight(lineW);
TrendRail.AssignValueColor(if isBull then Color.GREEN else Color.RED);

# Optional Fill Clouds
plot UpperRef = if showFill then activeRail + (railWidth * 0.5) else Double.NaN;
plot LowerRef = if showFill then activeRail - (railWidth * 0.5) else Double.NaN;

plot BullUpper = if showFill and isBull then UpperRef else Double.NaN;
plot BullLower = if showFill and isBull then LowerRef else Double.NaN;
AddCloud(BullUpper, BullLower, Color.DARK_GREEN, Color.DARK_GREEN);

plot BearUpper = if showFill and !isBull then UpperRef else Double.NaN;
plot BearLower = if showFill and !isBull then LowerRef else Double.NaN;
AddCloud(BearUpper, BearLower, Color.DARK_RED, Color.DARK_RED);

# Candle Coloring
AssignPriceColor(if paintCandles then (if isBull then Color.GREEN else Color.RED) else Color.CURRENT);

# Alerts
Alert(bullFlip, "Aroon Trend Rail turned bullish", Alert.BAR, Sound.Chimes);
Alert(bearFlip, "Aroon Trend Rail turned bearish", Alert.BAR, Sound.Bell);