var global = require('../internals/global');
var apply = require('../internals/function-apply');
var bind = require('../internals/function-bind-context');
var isCallable = require('../internals/is-callable');
var hasOwn = require('../internals/has-own-property');
var fails = require('../internals/fails');
var html = require('../internals/html');
var arraySlice = require('../internals/array-slice');
var createElement = require('../internals/document-create-element');
var IS_IOS = require('../internals/engine-is-ios');
var IS_NODE = require('../internals/engine-is-node');

var set = global.setImmediate;
var clear = global.clearImmediate;
var process = global.process;
var Dispatch = global.Dispatch;
var Function = global.Function;
var MessageChannel = global.MessageChannel;
var String = global.String;
var counter = 0;
var queue = {};
var ONREADYSTATECHANGE = 'onreadystatechange';
var location, defer, channel, port;

try {
  // Deno throws a ReferenceError on `location` access without `--location` flag
  location = global.location;
} catch (error) { /* empty */ }

var run = function (id) {
  if (hasOwn(queue, id)) {
    var fn = queue[id];
    delete queue[id];
    fn();
  }
};

var runner = function (id) {
  return function () {
    run(id);
  };
};

var listener = function (event) {
  run(event.data);
};

var post = function (id) {
  // old engines have not location.origin
  global.postMessage(String(id), location.protocol + '//' + location.host);
};

// Node.js 0.9+ & IE10+ has setImmediate, otherwise:
if (!set || !clear) {
  set = function setImmediate(fn) {
    var args = arraySlice(arguments, 1);
    queue[++counter] = function () {
      apply(isCallable(fn) ? fn : Function(fn), undefined, args);
    };
    defer(counter);
    return counter;
  };
  clear = function clearImmediate(id) {
    delete queue[id];
  };
  // Node.js 0.8-
  if (IS_NODE) {
    defer = function (id) {
      process.nextTick(runner(id));
    };
  // Sphere (JS game engine) Dispatch API
  } else if (Dispatch && Dispatch.now) {
    defer = function (id) {
      Dispatch.now(runner(id));
    };
  // Browsers with MessageChannel, includes WebWorkers
  // except iOS - https://github.com/zloirock/core-js/issues/624
  } else if (MessageChannel && !IS_IOS) {
    channel = new MessageChannel();
    port = channel.port2;
    channel.port1.onmessage = listener;
    defer = bind(port.postMessage, port);
  // Browsers with postMessage, skip WebWorkers
  // IE8 has postMessage, but it's sync & typeof its postMessage is 'object'
  } else if (
    global.addEventListener &&
    isCallable(global.postMessage) &&
    !global.importScripts &&
    location && location.protocol !== 'file:' &&
    !fails(post)
  ) {
    defer = post;
    global.addEventListener('message', listener, false);
  // IE8-
  } else if (ONREADYSTATECHANGE in createElement('script')) {
    defer = function (id) {
      html.appendChild(createElement('script'))[ONREADYSTATECHANGE] = function () {
        html.removeChild(this);
        run(id);
      };
    };
  // Rest old browsers
  } else {
    defer = function (id) {
      setTimeout(runner(id), 0);
    };
  }
}

module.exports = {
  set: set,
  clear: clear
};