1. save date in UTC
2. either two primary keys, or date as a primary key
3. search
4. https://developer.android.com/training/data-storage/use-cases?utm_source=lint&utm_medium=lint&utm_campaign=lint
5. https://developer.android.com/guide/topics/providers/document-provider.html#permissions
6. https://developer.android.com/training/data-storage/shared/documents-files
7. https://medium.cobeisfresh.com/taming-file-storage-on-android-part-1-16756ce91182
8. https://medium.com/@sendtosaeed2/android-fetch-all-files-from-local-storage-media-store-api-e9b914cd71e1