define(['./_isArrayLike', './keys', './_optimizeCb'], function (_isArrayLike, keys, _optimizeCb) {

  // Internal helper to create a reducing function, iterating left or right.
  function createReduce(dir) {
    // Wrap code that reassigns argument variables in a separate function than
    // the one that accesses `arguments.length` to avoid a perf hit. (#1991)
    var reducer = function(obj, iteratee, memo, initial) {
      var _keys = !_isArrayLike(obj) && keys(obj),
          length = (_keys || obj).length,
          index = dir > 0 ? 0 : length - 1;
      if (!initial) {
        memo = obj[_keys ? _keys[index] : index];
        index += dir;
      }
      for (; index >= 0 && index < length; index += dir) {
        var currentKey = _keys ? _keys[index] : index;
        memo = iteratee(memo, obj[currentKey], currentKey, obj);
      }
      return memo;
    };

    return function(obj, iteratee, memo, context) {
      var initial = arguments.length >= 3;
      return reducer(obj, _optimizeCb(iteratee, context, 4), memo, initial);
    };
  }

  return createReduce;

});
