number-name/src/Converter.ts

import Big from 'big.js'
import ConverterStream from './ConverterStream'
import { ReadStreamOptions, ConvertOptions, NumberSystem, Digit } from './common'

export default class Converter {
  constructor(private readonly system: NumberSystem, private options: ConvertOptions) {}

  public convert = (value: string | number | bigint): string => {
    let converted: string[] = []
    const valueStr = value as string
    switch (typeof value!) {
      case 'string':
        // TODO bail out when exponent is too large!
        try {
          return this.convert(BigInt(new Big(valueStr).toFixed()))
        } catch (e) {}
        return this.convert(BigInt(valueStr))
      case 'number':
        return this.convert(BigInt(value as number))
      case 'bigint':
        let current = value as bigint
        let thousandPower = 0n
        while (current > 0n) {
          const hundreds = Number(((current % 1000n) / 100n) % 10n) as Digit
          const tens = Number(((current % 100n) / 10n) % 10n) as Digit
          const ones = Number(current % 10n) as Digit

          let kiloName: string | undefined
          let kiloCount: string
          if (!(ones === 0 && tens === 0 && hundreds === 0)) {
            if (thousandPower > 0n) {
              const { scale = 'short' } = this.options
              kiloName = this.system.getKiloName[scale!]!(thousandPower)
            }
            kiloCount = this.system.getKiloCount(hundreds, tens, ones)
            converted.unshift(this.system.joinKilo(kiloCount, kiloName))
          }

          thousandPower = thousandPower + 1n
          current = current / 1000n
        }
        return converted.join(' ')
      default:
        break
    }
    throw TypeError('Invalid argument passed to value.')
  }

  public readStream = (streamOptions: ReadStreamOptions): ConverterStream => {
    return new ConverterStream(this.convert, streamOptions)
  }
}