Step #2: Defining a FilterMode

From the standpoint of the UI, we have three possible filter conditions:

• We want to show the completed to-do items
• We want to show the outstanding to-do items (i.e., the ones not yet completed)
• We want to show all items, regardless of completion status

That is beyond a simple Boolean value, but we can model that via an enum class.

In the ToDoRepository.kt source file, add this enum class before the ToDoRepository definition:

enum class FilterMode { ALL, OUTSTANDING, COMPLETED }