export function initNavOverflow() {
  const cluster = document.querySelector(".header__cluster");
  const nav = document.querySelector("[data-top-nav]");
  const moreWrap = document.querySelector("[data-nav-more]");
  const moreBtn = document.querySelector("[data-nav-more-btn]");
  const menuDock = document.querySelector("[data-nav-more-menu]");
  const menuFloating = document.querySelector("[data-nav-more-menu-floating]");
  const headerEl = document.querySelector(".header");
  if (!nav || !moreWrap || !moreBtn || !menuDock || !menuFloating || !headerEl) return;

  const links = Array.from(nav.querySelectorAll("a"));
  const MENU_GAP = 6;
  function getEdgePad() {
    const raw = getComputedStyle(document.documentElement).getPropertyValue("--edge-pad").trim();
    if (!raw) return 8;
    // resolve через временный элемент, т.к. значение — max(...clamp...)
    const probe = document.createElement("span");
    probe.style.all = "unset";
    probe.style.position = "fixed";
    probe.style.left = raw;
    document.body.appendChild(probe);
    const px = probe.getBoundingClientRect().left;
    probe.remove();
    return Math.max(0, Math.round(px));
  }
  let VIEWPORT_PAD = getEdgePad();
  let openInFloatingMode = null;
  let resizeRaf = 0;

  const isFloatingHeader = () => headerEl.classList.contains("header--scrolled");

  const moveOverflowToFloating = () => {
    while (menuDock.firstChild) menuFloating.appendChild(menuDock.firstChild);
  };
  const moveOverflowToDock = () => {
    while (menuFloating.firstChild) menuDock.appendChild(menuFloating.firstChild);
  };

  function closeMore() {
    moveOverflowToDock();
    menuDock.hidden = true;
    menuFloating.hidden = true;
    menuFloating.setAttribute("aria-hidden", "true");
    moreBtn.setAttribute("aria-expanded", "false");
    openInFloatingMode = null;
    menuFloating.style.removeProperty("--nav-more-menu-left");
    menuFloating.style.removeProperty("--nav-more-menu-top");
  }

  function placeMoreMenu() {
    if (menuFloating.hidden) return;
    const btnRect = moreBtn.getBoundingClientRect();
    const menuRect = menuFloating.getBoundingClientRect();
    const vw = document.documentElement.clientWidth;
    const vh = document.documentElement.clientHeight;

    let left = btnRect.right - menuRect.width;
    left = Math.min(left, vw - menuRect.width - VIEWPORT_PAD);
    left = Math.max(VIEWPORT_PAD, left);

    let top = btnRect.bottom + MENU_GAP;
    if (top + menuRect.height > vh - VIEWPORT_PAD) top = Math.max(VIEWPORT_PAD, btnRect.top - MENU_GAP - menuRect.height);

    menuFloating.style.setProperty("--nav-more-menu-left", `${Math.round(left)}px`);
    menuFloating.style.setProperty("--nav-more-menu-top", `${Math.round(top)}px`);
  }

  function navGapPx() {
    const cs = getComputedStyle(nav);
    const col = parseFloat(cs.columnGap);
    if (Number.isFinite(col)) return col;
    const row = parseFloat(cs.rowGap);
    if (Number.isFinite(row)) return row;
    const g = cs.gap;
    if (!g || g === "normal") return 0;
    const parts = String(g).trim().split(/\s+/);
    const n = parseFloat(parts.length > 1 ? parts[1] : parts[0]);
    return Number.isFinite(n) ? n : 0;
  }

  function rowContentWidth(el) {
    const gap = navGapPx();
    const kids = Array.from(el.children);
    let total = 0;
    kids.forEach((child, i) => {
      total += child.getBoundingClientRect().width;
      if (i > 0) total += gap;
    });
    return total;
  }

  function layoutLinks() {
    closeMore();
    links.forEach((link) => nav.appendChild(link));
    menuDock.innerHTML = "";
    menuFloating.innerHTML = "";
    moreWrap.hidden = true;

    if (rowContentWidth(nav) <= nav.clientWidth + 0.5) return;

    moreWrap.hidden = false;
    void nav.offsetWidth;
    while (rowContentWidth(nav) > nav.clientWidth + 0.5 && nav.children.length > 1) {
      const last = nav.lastElementChild;
      if (!last) break;
      menuDock.prepend(last);
    }
  }

  moreBtn.addEventListener("click", (e) => {
    e.stopPropagation();
    const open = menuDock.hidden && menuFloating.hidden;
    if (open) {
      openInFloatingMode = isFloatingHeader();
      if (openInFloatingMode) {
        moveOverflowToFloating();
        menuFloating.hidden = false;
        menuFloating.setAttribute("aria-hidden", "false");
      } else {
        menuDock.hidden = false;
      }
      moreBtn.setAttribute("aria-expanded", "true");
      requestAnimationFrame(() => {
        placeMoreMenu();
        requestAnimationFrame(placeMoreMenu);
      });
    } else {
      closeMore();
    }
  });

  document.addEventListener("click", (e) => {
    const t = e.target;
    if (!(t instanceof Node)) return;
    if (moreWrap.contains(t) || menuDock.contains(t) || menuFloating.contains(t)) {
      const el = t instanceof Element ? t : t.parentElement;
      if (el?.closest(".nav-more__dock a, .nav-more__floating a")) closeMore();
      return;
    }
    closeMore();
  });

  const onMenuLinkClick = (e) => {
    const t = e.target;
    const el = t instanceof Element ? t : t.parentElement;
    const a = el?.closest?.("a[href]");
    if (a && (menuDock.contains(a) || menuFloating.contains(a))) closeMore();
  };
  menuDock.addEventListener("click", onMenuLinkClick);
  menuFloating.addEventListener("click", onMenuLinkClick);

  const onResize = () => {
    if (resizeRaf) cancelAnimationFrame(resizeRaf);
    resizeRaf = requestAnimationFrame(() => {
      VIEWPORT_PAD = getEdgePad();
      layoutLinks();
      placeMoreMenu();
      resizeRaf = 0;
    });
  };
  window.addEventListener("resize", onResize, { passive: true });
  window.addEventListener(
    "scroll",
    () => {
      requestAnimationFrame(() => {
        if (openInFloatingMode !== null && isFloatingHeader() !== openInFloatingMode) closeMore();
        else placeMoreMenu();
      });
    },
    { passive: true },
  );
  window.addEventListener("load", layoutLinks, { once: true });
  layoutLinks();

  if (typeof ResizeObserver === "function" && cluster) {
    const ro = new ResizeObserver(() => {
      if (!menuDock.hidden || !menuFloating.hidden) return;
      layoutLinks();
    });
    ro.observe(cluster);
  }
}