Pig Latin

export const make = (text) => {
  const leadingVowel = /^([aeiouy]|[^aeiouy]+$)/i
  const leadingY = /^y/i
  const trailingY = /y$/i
  const fromFirstVowel = /[aeiouy].*$/i
  const toFirstVowel = /[^aeiouy]+/i

  return text
    .split(/\b/g)
    .map((token) => {
      if (!/[a-z]/i.test(token)) return token

      // Is this a standard case, or is there a leading vowel?
      let [front, back] = leadingVowel.test(token)
        ? [token, "yay"]
        : [token.match(fromFirstVowel)[0], token.match(toFirstVowel)[0] + "ay"]

      // Special case for y
      if (front.length > 1 && leadingY.test(front) && leadingY.test(back)) {
        front =
          front[0] === "y"
            ? front.slice(1)
            : front.slice(1, 2).toUpperCase() + front.slice(2)
      }

      // Flip capitalisation
      if (back[0] !== back[0].toLowerCase()) {
        back = back[0].toLowerCase() + back.slice(1)
        front = front[0].toUpperCase() + front.slice(1)
      }

      // Don't double "y" in the suffix
      if (trailingY.test(front) && leadingY.test(back)) {
        back = back.slice(1)
      }

      return front + back
    })
    .join("")
}