/**
* Bollinger Bands Width Indicator
* Measures the width between Bollinger Bands upper and lower bands
*/
import { calculateSMA } from './moving-averages'
export interface BBWidthData {
width: number | null
squeeze: 'extreme' | 'tight' | 'normal' | 'wide' | null
trend: 'expanding' | 'contracting' | 'stable' | null
}
export function calculateBBWidth(
closes: number[],
period: number = 20,
stdDev: number = 2
): BBWidthData {
// Minimum 5 data points required
if (closes.length < 5) {
return {
width: null,
squeeze: null,
trend: null,
}
}
// Use adaptive period
const effectivePeriod = Math.min(period, closes.length)
// 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 width
const width = (upperBand - lowerBand) / middleBand
// Determine squeeze level
let squeeze: 'extreme' | 'tight' | 'normal' | 'wide' | null = null
if (width < 0.02) squeeze = 'extreme' // Very tight bands
else if (width < 0.05) squeeze = 'tight' // Tight bands
else if (width > 0.15) squeeze = 'wide' // Wide bands
else squeeze = 'normal'
// Determine trend (simplified - would need historical data for proper trend)
let trend: 'expanding' | 'contracting' | 'stable' | null = null
if (closes.length >= effectivePeriod * 2) {
// Compare with previous period
const prevData = closes.slice(-(effectivePeriod * 2), -effectivePeriod)
const prevSMA = calculateSMA(prevData, effectivePeriod)
const prevMiddle = prevSMA.length > 0 ? prevSMA[prevSMA.length - 1] : prevData.reduce((a, b) => a + b, 0) / prevData.length
if (prevMiddle) {
const prevVariance = prevData.reduce((sum, value) => {
return sum + Math.pow(value - prevMiddle, 2)
}, 0) / effectivePeriod
const prevStdDev = Math.sqrt(prevVariance)
const prevUpper = prevMiddle + (prevStdDev * stdDev)
const prevLower = prevMiddle - (prevStdDev * stdDev)
const prevWidth = (prevUpper - prevLower) / prevMiddle
if (width > prevWidth * 1.1) trend = 'expanding'
else if (width < prevWidth * 0.9) trend = 'contracting'
else trend = 'stable'
}
}
return {
width,
squeeze,
trend,
}
}
