User script to show Fediverse links for bridged users on their Bluesky profiles

bbul.user.js

// ==UserScript==
// @name Bluesky Bridged User Labeler
// @match            https://bsky.app/*
// @version          1.6.2
// ==/UserScript==

// Link to your Fediverse instance (use "{handle}" as a template)
const FEDI_URL = "https://mastodon.social/@{handle}@bsky.brid.gy";

// Globals
const BRIDGE_ACTOR = "did:plc:xbifsywyv5pka5jlknhv5yv3";
const APPVIEW_API = "https://public.api.bsky.app/xrpc";
const CACHE = new Set();
let ACTIVE_TIMEOUT = null;

const addLink = async function(handle) {
  // Bsky hides soft-naved profiles, so we need to find the link from the visible one
  const followLink = Array.from(
    document.querySelectorAll('a[data-testid="profileHeaderFollowsButton"]')
  ).find((link) => link.checkVisibility());

  // sometimes script can get run before React has generated the profile page
  if (!followLink) {
    ACTIVE_TIMEOUT = setTimeout(addLink, 100, handle);
    return;
  }

  // avoid adding another Fediverse link if one already exists
  const profileMeta = followLink.parentElement;
  if (profileMeta.getElementsByClassName("bbul-link").length !== 0) {
    return;
  }

  const fedilink = document.createElement("a");
  fedilink.setAttribute("style", followLink.lastElementChild.getAttribute("style"));
  fedilink.style.textDecoration = "unset";
  fedilink.href = FEDI_URL.replace("{handle}", handle);
  fedilink.textContent = "Fediverse";
  fedilink.classList.add("bbul-link");
  profileMeta.append(fedilink);
  ACTIVE_TIMEOUT = null;
};

const checkHandle = async function() {
  // If timer is currently waiting for element, cancel it in case navigation has occurred
  if (ACTIVE_TIMEOUT !== null) {
    clearTimeout(ACTIVE_TIMEOUT);
    ACTIVE_TIMEOUT = null;
  }

  // get handle from title element (less race-y than document.location)
  const title = document.getElementsByTagName("title")[0].textContent;
  const parts = title.match(/\(@(.*)\) — Bluesky/);
  if (!parts) {
    return;
  }
  const handle = parts[parts.length - 1];

  // avoid hitting endpoint multiple times on soft navigation
  if (CACHE.has(handle)) {
    addLink(handle);
    return;
  }

  // get actor
  let resolveURL = `${APPVIEW_API}/com.atproto.identity.resolveHandle?handle=${handle}`;
  const resolveResponse = await fetch(resolveURL);
  if (!resolveResponse.ok) {
    console.log(`BBUL ERROR: ${resolveResponse.status}`);
    return;
  }
  const actorJSON = await resolveResponse.json();
  const actor = actorJSON.did;

  let relURL = `${APPVIEW_API}/app.bsky.graph.getRelationships?actor=${actor}&others=${BRIDGE_ACTOR}`;
  const relResponse = await fetch(relURL);
  if (!relResponse.ok) {
    console.log(`BBUL ERROR: ${relResponse.status}`);
    return;
  }
  const relationshipJSON = await relResponse.json();
  if (
    relationshipJSON.hasOwnProperty("relationships") && (
      relationshipJSON.relationships[0].hasOwnProperty("following") ||
      relationshipJSON.relationships[0].hasOwnProperty("followedBy")
  )) {
    CACHE.add(handle);
    addLink(handle);
  }
};

checkHandle();

// catch same-document navigations
const observer = new MutationObserver(function() {
  // can't filter on navigations by checking href, since same profile -> profile links can be clicked
  checkHandle();
});

observer.observe(document.getElementsByTagName("title")[0], {childList: true});