- ViewModel's managing the state of Timer
- TimerActivity's View, observe state from ViewModel, showing the right UI for each state, TimerActivity's also entry point for receiving user's interactions
- When app's in background, using AlarmManager for running the timer
- When app's in foreground, using CountDownTimer
- PerfUtils: Preferences helper functions are help to save time data for saving the previous timer, make sure when user resume app, the timer's still running
- TimerBackground: running timer in background interface, in implementation, it's using AlarmManager to handle timer when app's in background
- TimerExpiredReceiver: The BroadCastReceiver's reveiving event when the alarm manager's timer end
- TimerActivity: View
- TimerViewModel: ViewModel
- Utils: Time helper functions
