thermograph/frontend/static/nav.js

// Cross-view navigation + last-location memory. Remembers the most recently
// selected spot in localStorage and keeps the header's view links
// (Map · Calendar · Day · Compare) pointing at that spot — so switching views,
// or coming back to the map, lands you where you were instead of an empty map.

const LOC_KEY = "thermograph:loc";

function readStored() {
  try {
    const o = JSON.parse(localStorage.getItem(LOC_KEY));
    if (o && typeof o.lat === "number" && typeof o.lon === "number") return o;
  } catch (e) {}
  return null;
}

// Where should this page start? A hash (a shared/opened link) always wins;
// otherwise fall back to the last place the user looked at.
export function loadLastLocation() {
  const p = new URLSearchParams(location.hash.slice(1));
  const lat = parseFloat(p.get("lat")), lon = parseFloat(p.get("lon"));
  if (!isNaN(lat) && !isNaN(lon)) return { lat, lon, date: p.get("date") || null };
  return readStored();
}

// Remember a spot. Passing no `date` preserves whatever date was stored before,
// so hopping through the calendar (which has no date) doesn't wipe the day you
// were on elsewhere.
export function saveLastLocation(lat, lon, date) {
  let d = date;
  if (d === undefined) { const prev = readStored(); d = prev ? prev.date : null; }
  try { localStorage.setItem(LOC_KEY, JSON.stringify({ lat, lon, date: d || null })); } catch (e) {}
  refreshNav(lat, lon, d);
}

export function locHash(lat, lon, date) {
  let h = `#lat=${lat.toFixed(5)}&lon=${lon.toFixed(5)}`;
  if (date) h += `&date=${date}`;
  return h;
}

// Point every header view-link at the current spot so a tap keeps your place.
function refreshNav(lat, lon, date) {
  if (lat == null || lon == null) return;
  const h = locHash(lat, lon, date);
  document.querySelectorAll(".view-nav a[data-view]").forEach((a) => {
    a.href = (a.dataset.base || "") + h;
  });
}

// Point the header links at the current spot as soon as the page loads.
(function initNav() {
  document.querySelectorAll(".view-nav a[data-view]").forEach((a) => {
    a.dataset.base = a.getAttribute("href");
  });
  const loc = loadLastLocation();
  if (loc) refreshNav(loc.lat, loc.lon, loc.date);
})();

// Register the service worker so the app is installable and can receive Web Push
// (see sw.js). Base-relative, so it resolves under /thermograph automatically and
// takes /thermograph/ as its scope. A no-op in insecure contexts (plain-HTTP LAN)
// — registration just rejects and we swallow it; in-app features are unaffected.
if ("serviceWorker" in navigator && window.isSecureContext) {
  window.addEventListener("load", () => {
    navigator.serviceWorker.register("sw.js").catch(() => {});
  });
}