feat: add temperature unit preference

lib/weather-utils.ts

@@ -11,12 +11,19 @@ import type {
 import { translate, type Language } from "@/lib/i18n";
 import { getProvinceFromTeryt, normalizeProvinceName } from "@/lib/provinces";
 import type { CurrentWeatherCondition } from "@/types/imgw-current";
-import type { WindSpeedUnit } from "@/types/units";
+import type { TemperatureUnit, WindSpeedUnit } from "@/types/units";
 
 const locales: Record<Language, string> = { pl: "pl-PL", en: "en-GB" };
+export const DEFAULT_TEMPERATURE_UNIT: TemperatureUnit = "c";
+export const TEMPERATURE_UNITS: TemperatureUnit[] = ["c", "f"];
 export const DEFAULT_WIND_SPEED_UNIT: WindSpeedUnit = "ms";
 export const WIND_SPEED_UNITS: WindSpeedUnit[] = ["ms", "kmh", "mph"];
 
+const temperatureUnitLabels: Record<TemperatureUnit, string> = {
+  c: "°C",
+  f: "°F",
+};
+
 const windSpeedUnitLabels: Record<WindSpeedUnit, string> = {
   ms: "m/s",
   kmh: "km/h",
@@ -105,8 +112,28 @@ export function normalizeWarning(raw: RawWarning, kind: WarningKind, index: numb
   };
 }
 
-export function formatTemperature(value: number | null, language: Language = "pl") {
-  return value === null ? translate(language, "common.noData") : `${Math.round(value)}°`;
+export function isTemperatureUnit(value: unknown): value is TemperatureUnit {
+  return typeof value === "string" && TEMPERATURE_UNITS.includes(value as TemperatureUnit);
+}
+
+export function getTemperatureUnitLabel(unit: TemperatureUnit) {
+  return temperatureUnitLabels[unit];
+}
+
+export function convertTemperature(value: number, unit: TemperatureUnit) {
+  if (unit === "f") return (value * 9) / 5 + 32;
+  return value;
+}
+
+export function formatTemperatureValue(value: number, language: Language = "pl", unit: TemperatureUnit = DEFAULT_TEMPERATURE_UNIT) {
+  const formattedValue = new Intl.NumberFormat(locales[language], {
+    maximumFractionDigits: 0,
+  }).format(value);
+  return `${formattedValue}${getTemperatureUnitLabel(unit)}`;
+}
+
+export function formatTemperature(value: number | null, language: Language = "pl", unit: TemperatureUnit = DEFAULT_TEMPERATURE_UNIT) {
+  return value === null ? translate(language, "common.noData") : formatTemperatureValue(convertTemperature(value, unit), language, unit);
 }
 
 export function formatPressure(value: number | null, language: Language = "pl") {