const getRange = (start, end) => {
  let list = []
  if (start <= end) {
    for (let i = start; i <= end; i++)
      list.push(i)
  }
  return list
}

const RepeatableField = (fields, prefix) => ({

  expand: (num) =>
    getRange(1, num)
      .reduce((obj, num) => {
        obj[prefix + num] = Object.assign({}, fields)
        return obj
      }, {}),

  expandDependsOn (num, field) {
    const original = this.expand(num)
    const keys = Object.keys(original)

    return keys.reduce((obj, key, index) => {
      obj[key].dependsOn = {
        [field]: getRange(index + 1, num)
      }
      return obj
    }, original)
  },

  flatten: (original) =>
    Object.keys(original).reduce((obj, key) => {
      if (key.indexOf(prefix) === 0) {
        obj[prefix].push(original[key])
      } else {
        obj[key] = original[key]
      }
      return obj
    }, {
      [prefix]: []
    })())

})