Function convertArbitraryBaseBigIntVersion

Conversions/ArbitraryBase.js:73–117

(
  stringInBaseOne,
  baseOneCharacterString,
  baseTwoCharacterString
)

 * @returns {string}
 */
const convertArbitraryBaseBigIntVersion = (
  stringInBaseOne,
  baseOneCharacterString,
  baseTwoCharacterString
) => {
  if (
    [stringInBaseOne, baseOneCharacterString, baseTwoCharacterString]
      .map((arg) => typeof arg)
      .some((type) => type !== 'string')
  ) {
    throw new TypeError('Only string arguments are allowed')
  }

  const baseOneCharacters = [...baseOneCharacterString]
  const baseTwoCharacters = [...baseTwoCharacterString]

  for (const charactersInBase of [baseOneCharacters, baseTwoCharacters]) {
    if (charactersInBase.length !== new Set(charactersInBase).size) {
      throw new TypeError(
        'Duplicate characters in character set are not allowed'
      )
    }
  }
  const reversedStringOneChars = [...stringInBaseOne].reverse()
  const stringOneBase = BigInt(baseOneCharacters.length)
  let value = 0n
  let placeValue = 1n
  for (const digit of reversedStringOneChars) {
    const digitNumber = BigInt(baseOneCharacters.indexOf(digit))
    if (digitNumber === -1n) {
      throw new TypeError(`Not a valid character: ${digit}`)
    }
    value += digitNumber * placeValue
    placeValue *= stringOneBase
  }
  const outputChars = []
  const stringTwoBase = BigInt(baseTwoCharacters.length)
  while (value > 0n) {
    const divisionResult = value / stringTwoBase
    const remainder = value % stringTwoBase
    outputChars.push(baseTwoCharacters[remainder])
    value = divisionResult
  }
  return outputChars.reverse().join('') || baseTwoCharacters[0]
}

export { convertArbitraryBase, convertArbitraryBaseBigIntVersion }