/**
* Bollinger %B Indicator
* Shows where price is relative to Bollinger Bands
*/
import { calculateSMA } from './moving-averages'
export interface BBPercentBData {
percentB: number | null
position: 'below_lower' | 'near_lower' | 'middle' | 'near_upper' | 'above_upper' | null
signal: 'oversold' | 'neutral' | 'overbought' | null
}
export function calculateBBPercentB(
closes: number[],
period: number = 20,
stdDev: number = 2
): BBPercentBData {
// 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: number
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: 'below_lower' | 'near_lower' | 'middle' | 'near_upper' | 'above_upper' | null = 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: 'oversold' | 'neutral' | 'overbought' | null = null
if (percentB < 0.1) signal = 'oversold'
else if (percentB > 0.9) signal = 'overbought'
else signal = 'neutral'
return {
percentB,
position,
signal,
}
}
