muddle-ts/index.ts at main · typeclasses/muddle-ts · GitHub

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const re = /[a-zA-Z0-9]/

function match(x: string): boolean {
  return x.match(re) !== null
}

function countMatches(xs: string): number {
  let n = 0
  for (const x of xs) if (match(x)) n++
  return n
}

export type Options = {
  /**
   * A random generator. Should fill the array with uniformly
   * random bytes.
   */
  getRandomValues: ((a: Uint8Array) => void),

  /**
   * If sensitive, upper-case letters will not be changed to
   * lower case, and vice versa.
   *
   * Default: 'sensitive'
   */
  letterCase?: 'sensitive' | 'insensitive',

  /**
   * If sensitive, letters A-F will stay within that range. (This
   * prevents hexadecimal strings from becoming not hexadecimal.)
   *
   * Default: 'sensitive'
   */
  hexLetters?: 'sensitive' | 'insensitive',
}

export function muddle(input: string, options: Options): string {

  const letterCase = options.letterCase ?? 'sensitive'
  const hexLetters = options.hexLetters ?? 'sensitive'

  let n = countMatches(input)
  if (n === 0) return input

  const entropy = new Uint8Array(n)
  options.getRandomValues(entropy)

  let i = 0

  const output: Array<string> = []
  for (const x of input) {
    const y = x.codePointAt(0) as number

    if (y < 48) output.push(x)
    else if (y <= 57)
      output.push(String.fromCodePoint(48 + (entropy.at(i++) as number % 10)))
    else if (y < 65) output.push(x)
    else if (hexLetters === 'sensitive' && y <= 70) {
      if (letterCase === 'sensitive')
        output.push(String.fromCodePoint(65 + (entropy.at(i++) as number % 6)))
      else {
        const offset = entropy.at(i++) as number % (2 * 6)
        if (offset < 6)
          output.push(String.fromCodePoint(65 + offset))
        else
          output.push(String.fromCodePoint(97 + (offset - 6)))
      }
    }
    else if (y <= 90) {
      if (letterCase === 'sensitive')
        output.push(String.fromCodePoint(65 + (entropy.at(i++) as number % 26)))
      else {
        const offset = entropy.at(i++) as number % (2 * 26)
        if (offset < 26)
          output.push(String.fromCodePoint(65 + offset))
        else
          output.push(String.fromCodePoint(97 + (offset - 26)))
      }
    }
    else if (y < 97) output.push(x)
    else if (hexLetters === 'sensitive' && y <= 102) {
      if (letterCase === 'sensitive')
        output.push(String.fromCodePoint(97 + (entropy.at(i++) as number % 6)))
      else {
        const offset = entropy.at(i++) as number % (2 * 6)
        if (offset < 6)
          output.push(String.fromCodePoint(65 + offset))
        else
          output.push(String.fromCodePoint(97 + (offset - 6)))
      }
    }
    else if (y <= 122)
      if (letterCase === 'sensitive')
        output.push(String.fromCodePoint(97 + (entropy.at(i++) as number % 26)))
      else {
        const offset = entropy.at(i++) as number % (2 * 26)
        if (offset < 26)
          output.push(String.fromCodePoint(65 + offset))
        else
          output.push(String.fromCodePoint(97 + (offset - 26)))
      }
    else output.push(x)
  }
  return output.join('')
}