function cartesian(array) {
  function* cartesian(head, ...tail) {
    let remainder = tail.length ? cartesian(...tail) : [[]]
    for (let r of remainder) for (let h of head) yield [h, ...r]
  }

  return [...cartesian(...array)]
}

function deepKeys(object, separator = '.', prefix = '') {
  return Object.keys(object).reduce((result, key) => {
    if (Array.isArray(object[key])) {
      return [...result, prefix + key]
    } else if (typeof object[key] === 'object' && object[key] !== null) {
      return [...result, ...deepKeys(object[key], separator, prefix + key + separator)]
    }

    return [...result, prefix + key]
  }, [])
}

const extractTokens = pattern => pattern.split(/(?={[^}]+})|(?<={[^}]+})/)

const expandTokens = theme => tokens => {
  return tokens.map(token => {
    if (token.startsWith('{')) {
      const cleanToken = token.replace(/{|}/g, '')
      if (cleanToken.includes('.')) {
        const color = cleanToken.split('.')[1]
        const colorToken = {
          [color]: theme(cleanToken, {}),
        }
        return deepKeys(colorToken, '-')
      }
      return deepKeys(theme(cleanToken, {}), '-')
    } else {
      return [token]
    }
  })
}

const mapToClasses = expanded =>
  expanded.map(values => values.join('').replace('-DEFAULT', ''))

module.exports = theme => patterns => {
  return patterns // ["text-{gray}", …]
    .map(extractTokens) // [["text", "{gray}"], …]
    .map(expandTokens(theme)) // [[["text"], ["gray-100", "gray-200",…]], …]
    .map(cartesian) // [[["text", "gray-100"], ["text", "gray-200"], …], …]
    .flatMap(mapToClasses) // ["text-gray-100", "text-gray-200",…]
}