var pSlice = Array.prototype.slice;
var objectKeys = require('./lib/keys.js');
var isArguments = require('./lib/is_arguments.js');

var deepEqual = module.exports = function (actual, expected, opts) {
  if (!opts) opts = {};
  // 7.1. All identical values are equivalent, as determined by ===.
  if (actual === expected) {
    return true;

  } else if (actual instanceof Date && expected instanceof Date) {
    return actual.getTime() === expected.getTime();

  // 7.3. Other pairs that do not both pass typeof value == 'object',
  // equivalence is determined by ==.
  } else if (typeof actual != 'object' && typeof expected != 'object') {
    return opts.strict ? 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.
  } else {
    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) {
  var i, key;
  if (isUndefinedOrNull(a) || isUndefinedOrNull(b))
    return false;
  // an identical 'prototype' property.
  if (a.prototype !== b.prototype) return false;
  //~~~I've managed to break Object.keys through screwy arguments passing.
  //   Converting to array solves the problem.
  if (isArguments(a)) {
    if (!isArguments(b)) {
      return false;
    }
    a = pSlice.call(a);
    b = pSlice.call(b);
    return deepEqual(a, b, opts);
  }
  if (isBuffer(a)) {
    if (!isBuffer(b)) {
      return false;
    }
    if (a.length !== b.length) return false;
    for (i = 0; i < a.length; i++) {
      if (a[i] !== b[i]) return false;
    }
    return true;
  }
  try {
    var ka = objectKeys(a),
        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;
}
