content-script.js

const REWRITE_HOSTS = new Set([
  "twitter.com",
  "www.twitter.com",
  "fixupx.com",
  "www.fixupx.com"
]);

const REPLACEMENT_HOST = "x.com";
const REWRITTEN_ATTRIBUTE = "data-really-fixupx-rewritten";

function rewriteUrl(rawUrl) {
  let url;

  try {
    url = new URL(rawUrl, window.location.href);
  } catch {
    return rawUrl;
  }

  if (!REWRITE_HOSTS.has(url.hostname.toLowerCase())) {
    return rawUrl;
  }

  url.hostname = REPLACEMENT_HOST;
  return url.toString();
}

function rewriteText(text) {
  return text
    .replace(/\bhttps?:\/\/(?:www\.)?(?:x\.com|twitter\.com|fixupx\.com)\b/gi, (match) => {
      const protocol = match.startsWith("https://") ? "https://" : "http://";
      return `${protocol}${REPLACEMENT_HOST}`;
    })
    .replace(/\b(?:www\.)?(?:x\.com|twitter\.com|fixupx\.com)\b/gi, REPLACEMENT_HOST);
}

function rewriteElementAttributes(element) {
  for (const attributeName of ["href", "data-expanded-url", "data-url"]) {
    if (!element.hasAttribute(attributeName)) {
      continue;
    }

    const originalValue = element.getAttribute(attributeName);
    const rewrittenValue = rewriteUrl(originalValue);

    if (rewrittenValue !== originalValue) {
      element.setAttribute(attributeName, rewrittenValue);
      element.setAttribute(REWRITTEN_ATTRIBUTE, "true");
    }
  }
}

function rewriteVisibleLinkText(element) {
  const walker = document.createTreeWalker(element, NodeFilter.SHOW_TEXT);

  while (walker.nextNode()) {
    const textNode = walker.currentNode;
    const rewrittenText = rewriteText(textNode.nodeValue);

    if (rewrittenText !== textNode.nodeValue) {
      textNode.nodeValue = rewrittenText;
    }
  }
}

function rewriteNode(root) {
  if (root.nodeType !== Node.ELEMENT_NODE) {
    return;
  }

  const element = root;
  rewriteElementAttributes(element);

  if (element.matches("a")) {
    rewriteVisibleLinkText(element);
  }

  for (const child of element.querySelectorAll("a[href], [data-expanded-url], [data-url]")) {
    rewriteElementAttributes(child);

    if (child.matches("a")) {
      rewriteVisibleLinkText(child);
    }
  }
}

function installObserver() {
  const observer = new MutationObserver((mutations) => {
    for (const mutation of mutations) {
      if (mutation.type === "attributes") {
        rewriteNode(mutation.target);
        continue;
      }

      for (const node of mutation.addedNodes) {
        rewriteNode(node);
      }
    }
  });

  observer.observe(document.documentElement, {
    childList: true,
    subtree: true,
    attributes: true,
    attributeFilter: [
      "href",
      "data-expanded-url",
      "data-url"
    ]
  });
}

rewriteNode(document.documentElement);
installObserver();