tiny tracery, take two

minitrace-2.js

const randomInArray = arr => arr[Math.floor(Math.random() * arr.length)]
const isVowel = char => /^[aeiou]$/i.test(char)

const matcher = /\[([^\[\]]+)\]/g

export default function trace({concepts, concept, maxCycles = 10, seen = {}, modifierList = defaultModifiers}) {
  const [resolvedConcept, ...modifierChunks] = concept.split('|')
  const modifiers = modifierChunks
    .map(chunk => {
      const [modifierName, ...args] = chunk.split(' ')
      return [modifierList[modifierName], args]
    })
    .filter(resolved => resolved[0])

  if(!concepts[resolvedConcept]) {
    return `{error: unknown concept "${resolvedConcept}"}`
  }
  const traceResult = randomInArray(concepts[resolvedConcept])
    .replace(matcher, (_, nextConcept) => {
      if(seen[nextConcept] > maxCycles) {
        return '{error: max cycles exceeded}'
      }
      const nextSeen = Object.assign({}, seen)
      nextSeen[nextConcept] = nextSeen[nextConcept] + 1 || 1
      return trace({
        concepts,
        concept: nextConcept,
        maxCycles,
        seen: nextSeen
      })
    })
  return modifiers.reduce((result, m) => m[0](result, ...m[1]), traceResult)
}

var defaultModifiers = {
  s: word => {
    switch(word[word.length - 1].toLowerCase()) {
      case 's':
      case 'h':
      case 'x':
        return word + 'es'
      case 'y':
        return !isVowel(word[word.length - 2])
          ? word.substring(0, word.length - 1) + 'ies'
          : word + 's'
      default:
        return word + 's'
    }
  },
  a: word => {
    switch(true) {
      case word[0].toLowerCase() === 'u' && word.length > 2 && word[2].toLowerCase() === 'i':
      default:
        return 'a ' + word
      case isVowel(word[0]):
        return 'an ' + word
    }
  },
  ed : word => {
    switch(word[word.length - 1]) {
      case 'e':
        return word + 'd'
      case 'y':
        return word.length > 1 && !isVowel(word[word.length - 2])
          ? word.substring(0, word.length - 1) + 'ied'
          : word + 'd'
      default:
        return word + 'ed'
    }
  },
  ing : word => {
    if(word[word.length - 1].toLowerCase() === 'e')
      return word.substring(0, word.length - 1) + 'ing'
    return word + 'ing'
  },
  upper : word => word.toUpperCase(),
  cap : word => word[0].toUpperCase() + word.substring(1),
  swap : (word, search, replacement) => word.split(search).join(replacement)
}
defaultModifiers['an'] = defaultModifiers['a']
defaultModifiers['es'] = defaultModifiers['s']