(() => {
  const root = document.querySelector(".paper-shell");
  if (!root) return;

  const mapElement = document.getElementById("concept-map");
  let destinations = [];
  if (mapElement) {
    try {
      destinations = JSON.parse(mapElement.textContent);
    } catch (_) {
      document.documentElement.dataset.conceptLinksReady = "0";
    }
  }

  const termMap = new Map();
  for (const destination of destinations) {
    if (!document.getElementById(destination.target)) continue;
    for (const term of destination.terms || []) {
      termMap.set(term.toLocaleLowerCase(), destination);
    }
  }

  const terms = [...termMap.keys()].sort((a, b) => b.length - a.length);
  if (terms.length > 0) {
    const escaped = terms.map((term) =>
      term.replace(/[.*+?^${}()|[\]\\]/g, "\\$&")
    );
    const pattern = new RegExp(escaped.join("|"), "gi");
    const excluded = "a, code, pre, script, style, #human-review-inventory, #companion-details-panel, .source-anchor, .equation, .postulate, .resolution, .scope-box, .audit-disclosure, .route-details, .appendix-section, [data-concept-definition], .paper-footer, .toc";
    const linkedDestinationsByScope = new WeakMap();
    const walker = document.createTreeWalker(root, NodeFilter.SHOW_TEXT, {
      acceptNode(node) {
        if (!node.nodeValue.trim() || node.parentElement.closest(excluded)) {
          return NodeFilter.FILTER_REJECT;
        }
        return NodeFilter.FILTER_ACCEPT;
      }
    });

    const textNodes = [];
    while (walker.nextNode()) textNodes.push(walker.currentNode);

    for (const node of textNodes) {
      const text = node.nodeValue;
      const fragment = document.createDocumentFragment();
      const scope = node.parentElement.closest("section, header") || root;
      const linkedDestinations = linkedDestinationsByScope.get(scope) || new Set();
      linkedDestinationsByScope.set(scope, linkedDestinations);
      let cursor = 0;
      let changed = false;
      pattern.lastIndex = 0;

      for (const match of text.matchAll(pattern)) {
        const start = match.index;
        const end = start + match[0].length;
        const before = start > 0 ? text[start - 1] : "";
        const after = end < text.length ? text[end] : "";
        if (/[A-Za-z0-9]/.test(before) || /[A-Za-z0-9]/.test(after)) continue;

        const destination = termMap.get(match[0].toLocaleLowerCase());
        if (linkedDestinations.has(destination.target)) continue;
        fragment.append(document.createTextNode(text.slice(cursor, start)));
        const link = document.createElement("a");
        link.className = "concept-link";
        link.href = `#${destination.target}`;
        link.textContent = match[0];
        link.title = destination.label;
        fragment.append(link);
        linkedDestinations.add(destination.target);
        cursor = end;
        changed = true;
      }

      if (changed) {
        fragment.append(document.createTextNode(text.slice(cursor)));
        node.replaceWith(fragment);
      }
    }
  }

  document.documentElement.dataset.conceptLinksReady =
    String(document.querySelectorAll("a.concept-link").length);

  const returnButton = document.querySelector(".return-to-reading");
  let readingLink = null;
  if (returnButton) {
    root.addEventListener("click", (event) => {
      const link = event.target.closest("a.concept-link");
      if (!link) return;
      readingLink = link;
      returnButton.hidden = false;
    });

    returnButton.addEventListener("click", () => {
      if (!readingLink) return;
      try {
        history.replaceState(null, "", window.location.href.split("#")[0]);
      } catch (_) {
        /* Some file viewers do not permit history replacement. */
      }
      readingLink.focus({ preventScroll: true });
      readingLink.scrollIntoView({ block: "center" });
      returnButton.hidden = true;
    });
  }

  const tocLinks = [...document.querySelectorAll('.toc a[href^="#"]')];
  const tocTargets = tocLinks
    .map((link) => ({ link, section: document.querySelector(link.hash) }))
    .filter(({ section }) => section);

  const markCurrentSection = (id) => {
    for (const { link, section } of tocTargets) {
      if (section.id === id) link.setAttribute("aria-current", "location");
      else link.removeAttribute("aria-current");
    }
  };

  if ("IntersectionObserver" in window) {
    const sectionObserver = new IntersectionObserver((entries) => {
      const current = entries.find((entry) => entry.isIntersecting);
      if (current) markCurrentSection(current.target.id);
    }, { rootMargin: "-18% 0px -72%", threshold: 0 });
    for (const { section } of tocTargets) sectionObserver.observe(section);
  }
})();