/**
 * Copyright (c) 2013-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @typechecks
 * 
 */

/*eslint-disable no-self-compare */

'use strict';

var hasOwnProperty = Object.prototype.hasOwnProperty;

/**
 * inlined Object.is polyfill to avoid requiring consumers ship their own
 * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is
 */
function is(x, y) {
    // SameValue algorithm
    if (x === y) {
        // Steps 1-5, 7-10
        // Steps 6.b-6.e: +0 != -0
        // Added the nonzero y check to make Flow happy, but it is redundant
        return x !== 0 || y !== 0 || 1 / x === 1 / y;
    } else {
        // Step 6.a: NaN == NaN
        return x !== x && y !== y;
    }
}

/**
 * Performs equality by iterating through keys on an object and returning false
 * when any key has values which are not strictly equal between the arguments.
 * Returns true when the values of all keys are strictly equal.
 */
function shallowEqual(objA, objB) {
    if (is(objA, objB)) {
        return true;
    }

    if (typeof objA !== 'object' || objA === null || typeof objB !== 'object' || objB === null) {
        return false;
    }

    var keysA = Object.keys(objA);
    var keysB = Object.keys(objB);

    if (keysA.length !== keysB.length) {
        return false;
    }

    // Test for A's keys different from B.
    for (var i = 0; i < keysA.length; i++) {
        if (!hasOwnProperty.call(objB, keysA[i]) || !is(objA[keysA[i]], objB[keysA[i]])) {
            return false;
        }
    }

    return true;
}

export default shallowEqual