// These are Cloudflare's headers, taken from here:
// https://developers.cloudflare.com/fundamentals/reference/http-headers/
const CLOUDFLARE_HEADERS = new Set([
  'cf-connecting-ip',
  'cf-connecting-ipv6',
  'cf-ew-via',
  'cf-pseudo-ipv4',
  'cf-ray',
  'cf-ipcountry',
  'cf-visitor',
  'cf-worker'
]);

let blockingEnabled = true;
let stateLoaded = false;

const stateReady = browser.storage.local.get({ blockingEnabled: true })
  .then(result => { blockingEnabled = result.blockingEnabled; })
  .catch(() => { /* keep the default */ })
  .then(() => { stateLoaded = true; });

browser.storage.onChanged.addListener((changes, area) => {
  if (area === 'local' && changes.blockingEnabled) {
    blockingEnabled = changes.blockingEnabled.newValue;
  }
});

function blockedPageUrl(header, url) {
  const query = new URLSearchParams({
    name: header.name,
    value: header.value || '',
    url: url
  }).toString();
  return browser.runtime.getURL('blocked.html') + '?' + query;
}

function checkResponse(details) {
  if (!blockingEnabled) {
    return {};
  }

  const cfHeader = (details.responseHeaders || []).find(header =>
    CLOUDFLARE_HEADERS.has(header.name.toLowerCase())
  );
  if (!cfHeader) {
    return {};
  }

  if (details.type === 'main_frame') {
    return { redirectUrl: blockedPageUrl(cfHeader, details.url) };
  }

  // Subresource (image, script, stylesheet, font, iframe, fetch...): drop
  // just that request. The page itself keeps loading without it.
  // Makes the extension a bit more usable.
  return { cancel: true };
}

browser.webRequest.onHeadersReceived.addListener(
  details => stateLoaded
    ? checkResponse(details)
    : stateReady.then(() => checkResponse(details)),
  { urls: ['<all_urls>'] },
  ['blocking', 'responseHeaders']
);