// Units — the shared toggle and unit-aware formatting for every measure we show.
// The API always speaks imperial (°F, inches, mph); the unit is a pure display
// concern. Pages format through fmtTemp/fmtPrecip/fmtWind and re-render on
// `onUnitChange`, so stored and plotted values stay imperial and only the numbers
// shown flip.
//
// One flag drives all of them: picking °C also gives mm and km/h. A reader who
// wants Celsius wants the rest metric too, and a per-measure control would be
// three toggles in a header that has room for one. The button still shows °F/°C
// because temperature is what people look for.
//
// Absolute humidity (g/m³) is metric in both systems — there is no imperial unit
// for it anyone would recognise — so it is formatted here but never converted.
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
}
// A climate page knows which city it is about, so it publishes that country's
// convention on . It sits *between* the stored choice and
// the locale guess: better than the locale (a UK visitor reading about Phoenix
// wants the °F the page already rendered, and repainting it to °C would just be a
// flash), but never better than an explicit toggle. Pages with no single city —
// the homepage, the interactive views — emit no attribute and fall through.
function pageDefault() {
const v = document.body && document.body.dataset.unitDefault;
return (v === "C" || v === "F") ? v : null;
}
const _stored = localStorage.getItem(UNIT_KEY);
let _unit = (_stored === "C" || _stored === "F")
? _stored
: (pageDefault() || 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 : ""}`;
}
// --- precipitation (stored in inches) ----------------------------------------
const MM_PER_IN = 25.4;
// Inches as a number in the active unit.
export function toPrecip(vIn) { return _unit === "C" ? vIn * MM_PER_IN : vIn; }
// Millimetres are whole numbers — that is how rainfall is reported, and a tenth
// of a millimetre is below what the source resolves. Inches keep two decimals,
// since a whole inch of rain is a lot to round to.
// The suffix is " in"/" mm" to match what content.py renders server-side, so a
// climate page's repaint reproduces the text it shipped with rather than swapping
// the glyph. Compact surfaces (the tier bar) pass withUnit=false and add their own.
export function fmtPrecip(vIn, withUnit = true) {
if (vIn == null || isNaN(vIn)) return "—";
return _unit === "C"
? `${Math.round(vIn * MM_PER_IN)}${withUnit ? " mm" : ""}`
: `${vIn.toFixed(2)}${withUnit ? " in" : ""}`;
}
export const precipUnit = () => (_unit === "C" ? "mm" : "in");
// --- wind (stored in mph) ----------------------------------------------------
const KMH_PER_MPH = 1.609344;
export function toWind(vMph) { return _unit === "C" ? vMph * KMH_PER_MPH : vMph; }
export function fmtWind(vMph, withUnit = true) {
if (vMph == null || isNaN(vMph)) return "—";
const v = Math.round(toWind(vMph));
return `${v}${withUnit ? (_unit === "C" ? " km/h" : " mph") : ""}`;
}
export const windUnit = () => (_unit === "C" ? "km/h" : "mph");
// --- absolute humidity (g/m³ in both systems) --------------------------------
export function fmtHumid(v, withUnit = true) {
if (v == null || isNaN(v)) return "—";
return `${v.toFixed(1)}${withUnit ? " g/m³" : ""}`;
}
export const humidUnit = () => "g/m³";
export function onUnitChange(cb) { _unitCbs.push(cb); }
// --- unit symbols in prose ---------------------------------------------------
// Static copy that names a unit ("wind speed (mph)") marks it up as
// mph. The HTML ships the imperial symbol so
// there's something sensible with no JS; this keeps it honest once a unit is
// known. Runs on load and on every toggle, wherever units.js is imported.
const UNIT_LABEL = {
temp: () => `°${_unit}`,
precip: () => (_unit === "C" ? "mm" : "inches"),
wind: () => windUnit(),
humid: () => "g/m³",
};
function paintUnitLabels() {
for (const el of document.querySelectorAll("[data-unit-label]")) {
const f = UNIT_LABEL[el.dataset.unitLabel];
if (f) el.textContent = f();
}
}
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);
paintUnitLabels();
_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");
// Labelled for what it actually switches now — temperature, precipitation and
// wind — even though the buttons read °F/°C.
wrap.setAttribute("aria-label", "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);
})();
paintUnitLabels();