// Temperature units — the shared °C/°F toggle and unit-aware formatting.
// The API always speaks Fahrenheit; the unit is a pure display concern. Pages
// format temps through `fmtTemp`/`toUnit` and re-render on `onUnitChange`, so the
// stored/plotted values stay in °F and only the numbers shown flip.
const UNIT_KEY = "thermograph:unit";
// First-time default: pick °F only for the countries that actually use it (the US
// plus a handful of territories/nations), otherwise °C — read off the browser
// locale's region subtag (en-US → F, de-DE → C). A stored choice always wins, so
// this only affects visitors who've never toggled. Not persisted, so an unstored
// visitor keeps re-deriving the same locale default until they pick one.
const F_REGIONS = new Set(["US", "PR", "GU", "VI", "AS", "MP", "UM", "BS", "BZ", "KY", "PW", "FM", "MH", "LR"]);
function defaultUnit() {
const langs = (navigator.languages && navigator.languages.length)
? navigator.languages : [navigator.language];
for (const l of langs) {
const m = /-([A-Za-z]{2})\b/.exec(l || "");
if (m) return F_REGIONS.has(m[1].toUpperCase()) ? "F" : "C";
}
return "F"; // no region subtag to go on → keep the historical default
}
const _stored = localStorage.getItem(UNIT_KEY);
let _unit = (_stored === "C" || _stored === "F") ? _stored : defaultUnit();
const _unitCbs = [];
export function getUnit() { return _unit; }
// A Fahrenheit value as a number in the active unit.
export function toUnit(vF) { return _unit === "C" ? (vF - 32) * 5 / 9 : vF; }
// A Fahrenheit value formatted as a rounded temperature in the active unit.
// `withLetter` appends the C/F letter (off by default — the nav toggle shows it).
export function fmtTemp(vF, withLetter) {
if (vF == null || isNaN(vF)) return "—";
return `${Math.round(toUnit(vF))}°${withLetter ? _unit : ""}`;
}
// A Fahrenheit-degree *difference* (a span or tolerance, not an absolute
// reading) formatted in the active unit. Differences scale by 5/9 with no 32°
// offset, so they can't go through toUnit/fmtTemp.
export function fmtDelta(dF, withLetter) {
if (dF == null || isNaN(dF)) return "—";
const d = _unit === "C" ? dF * 5 / 9 : dF;
return `${Math.round(d)}°${withLetter ? _unit : ""}`;
}
export function onUnitChange(cb) { _unitCbs.push(cb); }
export function setUnit(u) {
const nu = (u === "C") ? "C" : "F";
if (nu === _unit) return;
_unit = nu;
try { localStorage.setItem(UNIT_KEY, _unit); } catch (e) {}
document.querySelectorAll(".unit-toggle").forEach(syncUnitToggle);
_unitCbs.forEach((cb) => { try { cb(_unit); } catch (e) {} });
}
function syncUnitToggle(wrap) {
wrap.querySelectorAll("button[data-unit]").forEach((b) => {
const on = b.dataset.unit === _unit;
b.classList.toggle("active", on);
b.setAttribute("aria-pressed", on ? "true" : "false");
});
}
// Drop a segmented °F/°C control into the header's top-right, ahead of the view
// switcher. A page opts out with data-no-unit-toggle on .
(function buildUnitToggle() {
const brand = document.querySelector(".brand");
if (!brand || brand.querySelector(".unit-toggle")) return;
if (document.body.dataset.noUnitToggle != null) return;
const wrap = document.createElement("div");
wrap.className = "unit-toggle";
wrap.setAttribute("role", "group");
wrap.setAttribute("aria-label", "Temperature units");
wrap.innerHTML = ''
+ '';
wrap.addEventListener("click", (e) => {
const b = e.target.closest("button[data-unit]");
if (b) setUnit(b.dataset.unit);
});
// Lives inside the nav menu panel: display:contents keeps it inline top-right
// on desktop; on phones it stacks inside the hamburger dropdown. Fall back to a
// brand sibling if the panel isn't present.
const panel = brand.querySelector(".nav-panel");
if (panel) panel.appendChild(wrap);
else brand.insertBefore(wrap, brand.querySelector(".view-nav"));
syncUnitToggle(wrap);
})();