Business Logic Component. Events go in, states come out. Separates UI from business logic using streams.

// BLoC pattern:
// UI sends Events -> BLoC
// BLoC emits States -> UI

// Event: what happened
abstract class CounterEvent {}
class Increment extends CounterEvent {}
class Decrement extends CounterEvent {}

// State: what to show
class CounterState {
  final int count;
  CounterState(this.count);
}