Location

const locations = [
  { name: 'Kraków', lat: 50.064651, lon: 19.944981 },
  { name: 'Tokio', lat: 39.758602, lon: -104.997437 },
  { name: 'New York', lat: 55.755825, lon: 37.617298 }
]

Location is uniquely identified by lat and long coordinates. That's why we need to pass them to each function dealing with Location entity, alternatively, we can choose to use UUID (generated on our side), then it will be possible to add two locations with the same coordinates and it will simplify Location operations (find by ID or ID as a key in store).

Application flow

After you add a new Location (action type: ADD_LOCATION) saga will catch that and fetch sunrise/sunset information from API.

Caching

Because sunrise/sunset data is immutable for given geolocation and date - we can cache it, that way going back and forth on calendar days will not trigger re-fetch. In a real-world app, this is either A) not needed B) number of cached items should be limited (memory limit on low-end phones).

With little effort we also have nice animations when we move between cached dates ;)