(function () {
  'use strict';

  // Full page reload for these form actions — logout intentionally kills the session.
  const FULL_RELOAD_ACTIONS = ['/logout'];

  function isSameOrigin(href) {
    try { return new URL(href, location.href).origin === location.origin; }
    catch { return false; }
  }

  // Swap #page-shell content, update title, and optionally push history.
  function applyPage(doc, finalUrl, pushState) {
    const newShell = doc.getElementById('page-shell');
    const curShell = document.getElementById('page-shell');
    if (newShell && curShell) curShell.innerHTML = newShell.innerHTML;
    document.title = doc.title;
    if (pushState) history.pushState({ btiNav: true }, doc.title, finalUrl);
    window.scrollTo(0, 0);
    window.dispatchEvent(new CustomEvent('briTunes:navigate'));
  }

  async function navigate(url, pushState) {
    if (pushState === undefined) pushState = true;
    try {
      const res = await fetch(url);
      if (!isSameOrigin(res.url)) { location.href = url; return; }
      const html = await res.text();
      applyPage(new DOMParser().parseFromString(html, 'text/html'), res.url, pushState);
    } catch {
      location.href = url;
    }
  }

  // Build the right body type for fetch POST:
  // - Forms with actual file selections → multipart FormData (multer handles it)
  // - All other forms → URL-encoded (express.urlencoded handles it)
  function buildBody(form) {
    const fd = new FormData(form);
    const hasFile = [...fd.values()].some(v => v instanceof File && v.size > 0);
    if (hasFile) return fd;
    const params = new URLSearchParams();
    for (const [k, v] of fd.entries()) {
      if (typeof v === 'string') params.append(k, v);
    }
    return params;
  }

  // --- Intercept link clicks ---
  document.addEventListener('click', (e) => {
    if (e.defaultPrevented || e.metaKey || e.ctrlKey || e.shiftKey || e.altKey) return;
    const a = e.target.closest('a[href]');
    if (!a) return;
    if (a.target && a.target !== '_self') return;
    if (a.hasAttribute('download')) return;
    const raw = a.getAttribute('href');
    if (!raw || raw.startsWith('#') || raw.startsWith('mailto:') || raw.startsWith('tel:')) return;
    if (!isSameOrigin(a.href)) return;
    e.preventDefault();
    navigate(a.href);
  });

  // --- Intercept form submissions ---
  document.addEventListener('submit', (e) => {
    const form = e.target;
    if (!(form instanceof HTMLFormElement)) return;
    if (!isSameOrigin(form.action)) return;

    const action = new URL(form.action, location.href).pathname;
    if (FULL_RELOAD_ACTIONS.some(ex => action.startsWith(ex))) return;

    const method = (form.method || 'GET').toUpperCase();

    if (method === 'GET') {
      // Rebuild URL with form data then navigate.
      e.preventDefault();
      const url = new URL(form.action, location.href);
      for (const [k, v] of new FormData(form).entries()) {
        if (typeof v === 'string') url.searchParams.set(k, v);
      }
      navigate(url.toString());
      return;
    }

    if (method === 'POST') {
      e.preventDefault();
      fetch(form.action, { method: 'POST', body: buildBody(form) })
        .then(async (res) => {
          if (!isSameOrigin(res.url)) { location.href = res.url; return; }
          const html = await res.text();
          applyPage(new DOMParser().parseFromString(html, 'text/html'), res.url, true);
        })
        .catch(() => form.submit());
    }
  });

  // --- Back / forward ---
  window.addEventListener('popstate', () => navigate(location.href, false));
})();