wip: Extract country list generation into utility

frontend/src/utils/countries.ts

@@ -0,0 +1,50 @@
+import iso3166 from "iso-3166-1";
+
+/**
+ * While the iso-3166-1 library does provide a country interface, said interface is not exported.
+ * We re-define it to make it usable for our purposes.
+ */
+export type Country = ReturnType<typeof iso3166.all>[number];
+
+// Define interface for divider/header items
+export interface CountryDivider {
+  divider: boolean;
+  header: string;
+}
+
+// Define a type that can be either a Country or a Divider
+export type CountryListItemType = Country | CountryDivider;
+
+// Get all countries from iso3166
+export const allCountries = iso3166.all() as Country[];
+
+// Get user's locale from browser (module-scoped)
+export const userLocale = navigator.language || navigator.languages?.[0] || 'en-US';
+export const userCountryCode = userLocale.split('-')[1]?.toUpperCase() || '';
+
+// Find user's country based on browser locale (module-scoped)
+export const userCountry = allCountries.find(c => c.alpha2 === userCountryCode);
+
+/**
+ * Prepares a list of countries with the user's country at the top (if available)
+ * @returns An array of countries and dividers for use in selection components
+ */
+export function getAvailableCountries(): CountryListItemType[] {
+
+  // Create the country list
+  const countries: CountryListItemType[] = [];
+
+  // Add user's country at the top if found
+  if (userCountry) {
+    countries.push(userCountry);
+    countries.push({ divider: true, header: 'All Countries' });
+
+    // Add all countries except the user's country to avoid duplicates
+    countries.push(...allCountries.filter(c => c.alpha2 !== userCountryCode));
+  } else {
+    // Add all countries if user's country not found
+    countries.push(...allCountries);
+  }
+
+  return countries;
+}