Function reduce

reduce(state: WidgetState, action: WidgetAction): WidgetState
Apply an action to the state, returning a new immutable WidgetState (the input is never mutated).
Parameters
- state: WidgetState
  The current state.
- action: WidgetAction
  The transition to apply; see WidgetAction.
Returns WidgetState
The next state. setMinute clamps the minute to [0, 1440] and recomputes date; setDate/setLng keep the solar minute-of-day and recompute date; setShadows/setEnabled just set the corresponding flag; an unknown action returns the input unchanged.