numerica/packages/core/src/utils/numeric.ts

import BigNumber from 'bignumber.js';

const EXPONENT_SEPARATOR = 'e';
const SIGNIFICAND_DECIMAL_POINT = '.';

export const NEGATIVE_SIGN = '-';

export const BLANK_DIGIT = '0'; // must be a value where Number(BLANK_DIGIT) === 0

export type Numeric = number | bigint | string | BigNumber

export type Group = [string, BigNumber]

export const normalizeNumeric = (x: Numeric): string => {
  try {
    switch (typeof x) {
    case 'number':
      return new BigNumber(x).toString(10);
    case 'bigint':
      return x.toString(10);
    case 'string':
      // TODO assume not all strings follow a correct format
      return x.trim();
      // return new BigNumber(x).toString(10)
    case 'object':
      return x.toString(10);
    default:
      break;
    }
  } catch {
    throw new RangeError('Not a valid numeric value in the current locale.');
  }
  throw new TypeError('Not a valid numeric value in any locale.');
};

export const deconstructNumeric = (x: string) => {
  const absolute = x.replaceAll(NEGATIVE_SIGN, '');
  if (!absolute.includes(EXPONENT_SEPARATOR)) {
    return {
      exponent: new BigNumber(absolute.length - 1),
      significandDigits: absolute,
    };
  }
  const [significandStrExp, exponentStr] = absolute.split(EXPONENT_SEPARATOR);
  const [integral] = significandStrExp.split(SIGNIFICAND_DECIMAL_POINT);
  return {
    exponent: new BigNumber(exponentStr).plus(integral.length - 1),
    significandDigits: significandStrExp.replaceAll(SIGNIFICAND_DECIMAL_POINT, ''),
  };
};

export const createBlankDigits = (grouping: number) => new Array<string>(grouping).fill(BLANK_DIGIT).join('');

export const groupDigits = (significandStr: string, exponent: BigNumber, grouping: number) => {
  const blankDigits = createBlankDigits(grouping);
  return significandStr
    .split('')
    .reduceRight(
      (theGroups, c, i): any => {
        const currentGroupIndex = exponent.minus(i).dividedToIntegerBy(grouping).minus(1);
        const [lastGroup = [blankDigits, currentGroupIndex.plus(1)] as Group] = theGroups;
        const [digits, groupIndex] = lastGroup;
        const currentPlaceValue = exponent.minus(i).mod(grouping);
        if (currentPlaceValue.eq(0)) {
          return [[`${blankDigits.slice(0, -c.length)}${c}`, currentGroupIndex.plus(1)], ...theGroups];
        }
        const currentDigitStringIndex = new BigNumber(grouping).minus(1).minus(currentPlaceValue).toNumber();
        const newDigits = digits.slice(
          0,
          currentDigitStringIndex,
        ) + c + digits.slice(currentDigitStringIndex + c.length);
        return [[newDigits, groupIndex] as Group, ...theGroups.slice(1)];
      },
      [] as Group[],
    );
};