var isNative = require('./isNative'),
    shimIsPlainObject = require('../internal/shimIsPlainObject');

/** `Object#toString` result references. */
var objectTag = '[object Object]';

/** Used for native method references. */
var objectProto = Object.prototype;

/**
 * Used to resolve the [`toStringTag`](https://people.mozilla.org/~jorendorff/es6-draft.html#sec-object.prototype.tostring)
 * of values.
 */
var objToString = objectProto.toString;

/** Native method references. */
var getPrototypeOf = isNative(getPrototypeOf = Object.getPrototypeOf) && getPrototypeOf;

/**
 * Checks if `value` is a plain object, that is, an object created by the
 * `Object` constructor or one with a `[[Prototype]]` of `null`.
 *
 * **Note:** This method assumes objects created by the `Object` constructor
 * have no inherited enumerable properties.
 *
 * @static
 * @memberOf _
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a plain object, else `false`.
 * @example
 *
 * function Foo() {
 *   this.a = 1;
 * }
 *
 * _.isPlainObject(new Foo);
 * // => false
 *
 * _.isPlainObject([1, 2, 3]);
 * // => false
 *
 * _.isPlainObject({ 'x': 0, 'y': 0 });
 * // => true
 *
 * _.isPlainObject(Object.create(null));
 * // => true
 */
var isPlainObject = !getPrototypeOf ? shimIsPlainObject : function(value) {
  if (!(value && objToString.call(value) == objectTag)) {
    return false;
  }
  var valueOf = value.valueOf,
      objProto = isNative(valueOf) && (objProto = getPrototypeOf(valueOf)) && getPrototypeOf(objProto);

  return objProto
    ? (value == objProto || getPrototypeOf(value) == objProto)
    : shimIsPlainObject(value);
};

module.exports = isPlainObject;