setup(_ => {
  assert_implements_optional(
    document.createElement('link').relList.supports('prefetch'),
    "Browser supports prefetch.");
  assert_implements_optional(
    "PerformanceResourceTiming" in window,
    "Browser supports performance APIs.");
});

async function waitUntilResourceDownloaded(url) {
  await new Promise((resolve, reject) => {
    if (performance.getEntriesByName(url).length >= 1)
      resolve();

    let observer = new PerformanceObserver(list => {
      list.getEntries().forEach(entry => {
        if (entry.name == url) {
          resolve();
        }
      });
    });
  });
}

function assert_resource_not_downloaded(test, url) {
  // CSP failures generate resource timing entries, so let's make sure that
  // download sizes are 0.
  const entries = performance.getEntriesByName(url, 'resource');
  for (const entry of entries) {
    assert_equals(entry.transferSize, 0, 'transferSize');
    assert_equals(entry.encodedBodySize, 0, 'encodedBodySize');
    assert_equals(entry.decodedBodySize, 0, 'decodedBodySize');
  }
}

function assert_link_prefetches(test, link) {
  assert_no_csp_event_for_url(test, link.href);

  link.onerror = test.unreached_func('onerror should not fire.');

  // Test is finished when either the `load` event fires, or we get a performance
  // entry showing that the resource loaded successfully.
  link.onload = test.step_func(test.step_func_done());
  waitUntilResourceDownloaded(link.href).then(test.step_func_done());

  document.head.appendChild(link);
}

function assert_link_does_not_prefetch(test, link) {
  let cspEvent = false;
  let errorEvent = false;

  waitUntilCSPEventForURL(test, link.href)
      .then(test.step_func(e => {
        cspEvent = true;
        assert_equals(e.violatedDirective, "prefetch-src");
        assert_equals(e.effectiveDirective, "prefetch-src");

        if (errorEvent)
          test.done();
      }));

  link.onerror = test.step_func(e => {
    errorEvent = true;
    if (cspEvent)
      test.done();
  });
  link.onload = test.unreached_func('onload should not fire.');

  document.head.appendChild(link);
}