@0xtorch/big-decimal/toStringBigDecimal.ts

An arbitrary precision Decimal type for TypeScript that extends BigInt.

import type { BigDecimal } from './type'

export const toStringBigDecimal = ({ value, decimals }: BigDecimal): string => {
  if (value === 0n) {
    return '0'
  }

  const isNegative = value < 0
  const prefix = isNegative ? '-' : ''
  const absValue = isNegative ? -value : value
  const valueText = absValue.toString()
  const valueLength = valueText.length
  const decimalLength = decimals
  if (valueLength <= decimalLength) {
    const text = `0.${valueText.padStart(decimalLength, '0')}`
    const formattedText = text.replace(/0+$/, '')
    return `${prefix}${formattedText}`
  }
  const intText = valueText.slice(0, valueLength - decimalLength)
  const decimalText = valueText.slice(valueLength - decimalLength)
  // decimal 末尾の 0 は削除 (正規表現で良い感じに)
  const formattedDecimalText = decimalText.replace(/0+$/, '')
  if (formattedDecimalText.length === 0) {
    return `${prefix}${intText}`
  }
  return `${prefix}${intText}.${formattedDecimalText}`
}