function ok(a, msg) {
  postMessage({ type: "check", check: !!a, message: msg });
}

function is(a, b, msg) {
  ok(a === b, msg);
}

function info(msg) {
  postMessage({ type: "info", message: msg });
}

function finish() {
  postMessage({ type: "finish" });
}

function basic() {
  var a = new MessageChannel();
  ok(a, "MessageChannel created");

  var port1 = a.port1;
  ok(port1, "MessageChannel.port1 exists");
  is(port1, a.port1, "MessageChannel.port1 is port1");

  var port2 = a.port2;
  ok(port2, "MessageChannel.port1 exists");
  is(port2, a.port2, "MessageChannel.port2 is port2");

  ["postMessage", "start", "close"].forEach(function (e) {
    ok(e in port1, "MessagePort1." + e + " exists");
    ok(e in port2, "MessagePort2." + e + " exists");
  });

  runTests();
}

function sendMessages() {
  var a = new MessageChannel();
  ok(a, "MessageChannel created");

  a.port1.postMessage("Hello world!");
  a.port1.onmessage = function (e) {
    is(e.data, "Hello world!", "The message is back!");
    runTests();
  };

  a.port2.onmessage = function (e) {
    a.port2.postMessage(e.data);
  };
}

function transferPort() {
  var a = new MessageChannel();
  ok(a, "MessageChannel created");

  a.port1.postMessage("Hello world!");
  a.port1.onmessage = function (e) {
    is(e.data, "Hello world!", "The message is back!");
    runTests();
  };

  postMessage({ type: "port" }, [a.port2]);
}

function transferPort2() {
  onmessage = function (evt) {
    is(evt.ports.length, 1, "A port has been received by the worker");
    evt.ports[0].onmessage = function (e) {
      is(e.data, 42, "Data is 42!");
      runTests();
    };
  };

  postMessage({ type: "newport" });
}

var tests = [basic, sendMessages, transferPort, transferPort2];

function runTests() {
  if (!tests.length) {
    finish();
    return;
  }

  var t = tests.shift();
  t();
}

var subworker;
onmessage = function (evt) {
  if (evt.data == 0) {
    runTests();
    return;
  }

  if (!subworker) {
    info("Create a subworkers. ID: " + evt.data);
    subworker = new Worker("worker_messageChannel.js");
    subworker.onmessage = function (e) {
      info("Proxy a message to the parent.");
      postMessage(e.data, e.ports);
    };

    subworker.postMessage(evt.data - 1);
    return;
  }

  info("Dispatch a message to the subworker.");
  subworker.postMessage(evt.data, evt.ports);
};