var objectKeys = require('object-keys');
var isArguments = require('is-arguments');
var is = require('object-is');
var isRegex = require('is-regex');
var flags = require('regexp.prototype.flags');
var isDate = require('is-date-object');

var getTime = Date.prototype.getTime;

function deepEqual(actual, expected, options) {
  var opts = options || {};

  // 7.1. All identical values are equivalent, as determined by ===.
  if (opts.strict ? is(actual, expected) : actual === expected) {
    return true;
  }

  // 7.3. Other pairs that do not both pass typeof value == 'object', equivalence is determined by ==.
  if (!actual || !expected || (typeof actual !== 'object' && typeof expected !== 'object')) {
    return opts.strict ? is(actual, expected) : actual == expected;
  }

  /*
   * 7.4. For all other Object pairs, including Array objects, equivalence is
   * determined by having the same number of owned properties (as verified
   * with Object.prototype.hasOwnProperty.call), the same set of keys
   * (although not necessarily the same order), equivalent values for every
   * corresponding key, and an identical 'prototype' property. Note: this
   * accounts for both named and indexed properties on Arrays.
   */
  // eslint-disable-next-line no-use-before-define
  return objEquiv(actual, expected, opts);
}

function isUndefinedOrNull(value) {
  return value === null || value === undefined;
}

function isBuffer(x) {
  if (!x || typeof x !== 'object' || typeof x.length !== 'number') {
    return false;
  }
  if (typeof x.copy !== 'function' || typeof x.slice !== 'function') {
    return false;
  }
  if (x.length > 0 && typeof x[0] !== 'number') {
    return false;
  }
  return true;
}

function objEquiv(a, b, opts) {
  /* eslint max-statements: [2, 50] */
  var i, key;
  if (typeof a !== typeof b) { return false; }
  if (isUndefinedOrNull(a) || isUndefinedOrNull(b)) { return false; }

  // an identical 'prototype' property.
  if (a.prototype !== b.prototype) { return false; }

  if (isArguments(a) !== isArguments(b)) { return false; }

  var aIsRegex = isRegex(a);
  var bIsRegex = isRegex(b);
  if (aIsRegex !== bIsRegex) { return false; }
  if (aIsRegex || bIsRegex) {
    return a.source === b.source && flags(a) === flags(b);
  }

  if (isDate(a) && isDate(b)) {
    return getTime.call(a) === getTime.call(b);
  }

  var aIsBuffer = isBuffer(a);
  var bIsBuffer = isBuffer(b);
  if (aIsBuffer !== bIsBuffer) { return false; }
  if (aIsBuffer || bIsBuffer) { // && would work too, because both are true or both false here
    if (a.length !== b.length) { return false; }
    for (i = 0; i < a.length; i++) {
      if (a[i] !== b[i]) { return false; }
    }
    return true;
  }

  if (typeof a !== typeof b) { return false; }

  try {
    var ka = objectKeys(a);
    var kb = objectKeys(b);
  } catch (e) { // happens when one is a string literal and the other isn't
    return false;
  }
  // having the same number of owned properties (keys incorporates hasOwnProperty)
  if (ka.length !== kb.length) { return false; }

  // the same set of keys (although not necessarily the same order),
  ka.sort();
  kb.sort();
  // ~~~cheap key test
  for (i = ka.length - 1; i >= 0; i--) {
    if (ka[i] != kb[i]) { return false; }
  }
  // equivalent values for every corresponding key, and ~~~possibly expensive deep test
  for (i = ka.length - 1; i >= 0; i--) {
    key = ka[i];
    if (!deepEqual(a[key], b[key], opts)) { return false; }
  }

  return true;
}

module.exports = deepEqual;