number-name/src/systems/en/base/kilo/combiningPrefix.ts

import NAMES from '../../names.json'
import ones from './ones'
import tens from './tens'
import hundreds from './hundreds'

interface CombiningPrefix {
  (kiloHundreds: number, kiloTens: number, kiloOnes: number, kiloPower?: number): string
}

const combiningPrefix: CombiningPrefix = (kiloHundredsRaw, kiloTens, kiloOnes, kiloPower = 0) => {
  let kiloHundreds = kiloHundredsRaw
  let prefix = ''

  const isMillia = kiloHundredsRaw >= 10
  if (isMillia) {
    prefix += combiningPrefix(
      Math.floor(kiloHundredsRaw / 1000),
      Math.floor((kiloHundredsRaw / 100) % 10),
      Math.floor((kiloHundredsRaw / 10) % 10),
      kiloPower + 1,
    )
    kiloHundreds = kiloHundredsRaw % 10
  }

  const hasHundreds = kiloHundreds > 0
  if (hasHundreds) {
    prefix += hundreds(kiloHundreds)
  }

  if (
    kiloPower > 0 &&
    ((kiloHundreds === 0 && kiloTens === 0 && kiloOnes > 1) ||
      ((kiloHundreds > 0 || kiloTens > 0) && kiloOnes > 0) ||
      (kiloHundreds === 0 && kiloTens === 0 && kiloOnes === 1 && prefix.endsWith(NAMES.kiloThousand)))
  ) {
    // http://www.isthe.com/chongo/tech/math/number/howhigh.html
    // Section: Titanic size numbers < 10^3000003
    prefix += ones(kiloOnes, false)
  }
  if (kiloPower === 0 && kiloOnes > 0) {
    const special = kiloHundreds === 0 && kiloTens === 0
    prefix += ones(kiloOnes, special)
    if (special && [5, 6].includes(kiloOnes)) {
      prefix += 't'
    }
  }
  if (kiloTens > 0) {
    prefix += tens(kiloTens)
  }

  if (kiloPower > 0) {
    if (!(kiloHundreds === 0 && kiloTens === 0 && kiloOnes === 0)) {
      for (let p = 0; p < kiloPower; p += 1) {
        prefix += NAMES.kiloThousand
      }
    }
    return prefix
  }

  if ((kiloHundreds === 0 && kiloTens > 1) || (kiloHundreds > 0 && kiloTens !== 1) || kiloHundredsRaw >= 10) {
    prefix += 't'
  }
  return prefix + 'i'
}

export default combiningPrefix