first commit

calcom/packages/lib/cityTimezonesHandler.ts

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+import { cityMapping as allCities } from "city-timezones";
+
+export type CityTimezones = Awaited<ReturnType<typeof cityTimezonesHandler>>;
+
+export const cityTimezonesHandler = async () => {
+  /**
+   * Filter out all cities that have the same "city" key and only use the one with the highest population.
+   * This way we return a new array of cities without running the risk of having more than one city
+   * with the same name on the dropdown and prevent users from mistaking the time zone of the desired city.
+   */
+  const topPopulatedCities: { [key: string]: { city: string; timezone: string; pop: number } } = {};
+  allCities.forEach((city) => {
+    const cityPopulationCount = city.pop;
+    if (
+      topPopulatedCities[city.city]?.pop === undefined ||
+      cityPopulationCount > topPopulatedCities[city.city].pop
+    ) {
+      topPopulatedCities[city.city] = { city: city.city, timezone: city.timezone, pop: city.pop };
+    }
+  });
+  const uniqueCities = Object.values(topPopulatedCities);
+  /** Add specific overries in here */
+  uniqueCities.forEach((city) => {
+    if (city.city === "London") city.timezone = "Europe/London";
+    if (city.city === "Londonderry") city.city = "London";
+  });
+
+  return uniqueCities;
+};
+
+export default cityTimezonesHandler;