'use strict';
var $ = require('../internals/export');
var anObject = require('../internals/an-object');
var aCallable = require('../internals/a-callable');
var getMapIterator = require('../internals/get-map-iterator');
var iterate = require('../internals/iterate');

var $TypeError = TypeError;

// `Map.prototype.reduce` method
// https://github.com/tc39/proposal-collection-methods
$({ target: 'Map', proto: true, real: true, forced: true }, {
  reduce: function reduce(callbackfn /* , initialValue */) {
    var map = anObject(this);
    var iterator = getMapIterator(map);
    var noInitial = arguments.length < 2;
    var accumulator = noInitial ? undefined : arguments[1];
    aCallable(callbackfn);
    iterate(iterator, function (key, value) {
      if (noInitial) {
        noInitial = false;
        accumulator = value;
      } else {
        accumulator = callbackfn(accumulator, value, key, map);
      }
    }, { AS_ENTRIES: true, IS_ITERATOR: true });
    if (noInitial) throw $TypeError('Reduce of empty map with no initial value');
    return accumulator;
  }
});