/**
 * Returns a copy of the list, sorted by provided key according to the
 * comparator function.
 *
 * Note that this is a copy of the list. It does not modify the original.
 *
 * @param {String} key .
 * @param {Array} list .
 * @param {Function} fn .
 * @param {Boolean} desc .
 * @return {Array} A new list sorted by the keys generated by `fn`.
 * @example
 *
 *   const users = [
 *     { 'user': 'ed',   'age': 36 },
 *     { 'user': 'fer', 'age': 34 },
 *     { 'user': 'ivan',   'age': 35 },
 *     { 'user': 'inma', 'age': 32 }
 *   ]
 *
 *   sortBy('age', users, parseInt, false)
 *   // [
 *   //   { 'user': 'inma', 'age': 32 },
 *   //   { 'user': 'fer', 'age': 34 },
 *   //   { 'user': 'ivan',   'age': 35 },
 *   //   { 'user': 'ed',   'age': 36 }
 *   // ]
 *
 */

const baseSortBy = (key, fn, desc = false) => {
  const _key = fn ? (x) => fn(x[key]) : (x) => x[key]
  desc = !desc ? 1 : -1
  return (a, b) => {
    return a = _key(a), b = _key(b), desc * ((a > b) - (b > a))
  }
}

const sortBy = (key, list, fn, desc = false) => Array.prototype.slice.call(list, 0).sort(baseSortBy(key, fn, desc))

export default sortBy