/**
* Bollinger %B Indicator
* Shows where price is relative to Bollinger Bands
*/
import { calculateSMA } from './moving-averages';
export function calculateBBPercentB(closes, period = 20, stdDev = 2) {
// Minimum 5 data points required
if (closes.length < 5) {
return {
percentB: null,
position: null,
signal: null,
};
}
// Use adaptive period
const effectivePeriod = Math.min(period, closes.length);
const currentPrice = closes[closes.length - 1];
// Calculate SMA for middle band
const sma = calculateSMA(closes, effectivePeriod);
let middleBand;
if (sma.length === 0) {
// Fallback: use simple average
middleBand = closes.slice(-effectivePeriod).reduce((a, b) => a + b, 0) / effectivePeriod;
}
else {
middleBand = sma[sma.length - 1];
}
// Calculate standard deviation
const recentData = closes.slice(-effectivePeriod);
const variance = recentData.reduce((sum, value) => {
return sum + Math.pow(value - middleBand, 2);
}, 0) / effectivePeriod;
const standardDeviation = Math.sqrt(variance);
// Calculate bands
const upperBand = middleBand + (standardDeviation * stdDev);
const lowerBand = middleBand - (standardDeviation * stdDev);
// Calculate %B
const bandWidth = upperBand - lowerBand;
const percentB = bandWidth !== 0 ? (currentPrice - lowerBand) / bandWidth : 0.5;
// Determine position
let position = null;
if (percentB < 0)
position = 'below_lower';
else if (percentB < 0.2)
position = 'near_lower';
else if (percentB < 0.8)
position = 'middle';
else if (percentB < 1.0)
position = 'near_upper';
else
position = 'above_upper';
// Determine signal
let signal = null;
if (percentB < 0.1)
signal = 'oversold';
else if (percentB > 0.9)
signal = 'overbought';
else
signal = 'neutral';
return {
percentB,
position,
signal,
};
}
