var baseFlatten = require('./_baseFlatten'),
    baseOrderBy = require('./_baseOrderBy'),
    isArray = require('./isArray'),
    isFlattenableIteratee = require('./_isFlattenableIteratee'),
    isIterateeCall = require('./_isIterateeCall'),
    rest = require('./rest');

/**
 * Creates an array of elements, sorted in ascending order by the results of
 * running each element in a collection thru each iteratee. This method
 * performs a stable sort, that is, it preserves the original sort order of
 * equal elements. The iteratees are invoked with one argument: (value).
 *
 * @static
 * @memberOf _
 * @since 0.1.0
 * @category Collection
 * @param {Array|Object} collection The collection to iterate over.
 * @param {...(Array|Array[]|Function|Function[]|Object|Object[]|string|string[])}
 *  [iteratees=[_.identity]] The iteratees to sort by.
 * @returns {Array} Returns the new sorted array.
 * @example
 *
 * var users = [
 *   { 'user': 'fred',   'age': 48 },
 *   { 'user': 'barney', 'age': 36 },
 *   { 'user': 'fred',   'age': 40 },
 *   { 'user': 'barney', 'age': 34 }
 * ];
 *
 * _.sortBy(users, function(o) { return o.user; });
 * // => objects for [['barney', 36], ['barney', 34], ['fred', 48], ['fred', 40]]
 *
 * _.sortBy(users, ['user', 'age']);
 * // => objects for [['barney', 34], ['barney', 36], ['fred', 40], ['fred', 48]]
 *
 * _.sortBy(users, 'user', function(o) {
 *   return Math.floor(o.age / 10);
 * });
 * // => objects for [['barney', 36], ['barney', 34], ['fred', 48], ['fred', 40]]
 */
var sortBy = rest(function(collection, iteratees) {
  if (collection == null) {
    return [];
  }
  var length = iteratees.length;
  if (length > 1 && isIterateeCall(collection, iteratees[0], iteratees[1])) {
    iteratees = [];
  } else if (length > 2 && isIterateeCall(iteratees[0], iteratees[1], iteratees[2])) {
    iteratees = [iteratees[0]];
  }
  iteratees = (iteratees.length == 1 && isArray(iteratees[0]))
    ? iteratees[0]
    : baseFlatten(iteratees, 1, isFlattenableIteratee);

  return baseOrderBy(collection, iteratees, []);
});

module.exports = sortBy;
