number-name/src/ConverterStream.ts

import { Transform } from 'stream'
import { Digit, NumberSystem, ReadStreamOptions } from './common'

export default class ConverterStream extends Transform {
  private thousandPower: bigint = 0n

  constructor(private readonly system: NumberSystem, private readonly options: ReadStreamOptions) {
    super()
    this.thousandPower = 0n
  }

  _transform(chunk: Buffer, _encoding: BufferEncoding, callback: Function) {
    const { scale, encoding } = this.options

    const [ones = 0, tens = 0, hundreds = 0] = chunk
      .toString(encoding!)
      .split('')
      .filter((s: string) => /[0-9]/.test(s))
      .map((d: string) => Number(d)) // todo use encoding

    if (!(ones === 0 && tens === 0 && hundreds === 0)) {
      if (this.thousandPower > 0) {
        this.push(
          this.system.getKiloName[scale!]!(this.thousandPower)
            .split('')
            .reverse()
            .join(''),
        )
        this.push(' ')
      }
      this.push(
        this.system
          .getKiloCount(hundreds as Digit, tens as Digit, ones as Digit)
          .split('')
          .reverse()
          .join(''),
      )
      this.push(' ')
    }

    this.thousandPower = this.thousandPower + 1n
    callback()
  }
}