Bloc, Cubit and choosing an approach

import 'package:flutter_bloc/flutter_bloc.dart';

class CounterCubit extends Cubit<int> {
  CounterCubit() : super(0);            // initial state

  void increment() => emit(state + 1);  // emit a new state
  void reset() => emit(0);
}

sealed class LoginEvent {}
class LoginSubmitted extends LoginEvent {
  LoginSubmitted(this.mobile);
  final String mobile;
}

sealed class LoginState {}
class LoginInitial extends LoginState {}
class LoginLoading extends LoginState {}
class LoginSuccess extends LoginState {}
class LoginFailure extends LoginState {
  LoginFailure(this.message);
  final String message;
}

class LoginBloc extends Bloc<LoginEvent, LoginState> {
  LoginBloc() : super(LoginInitial()) {
    on<LoginSubmitted>((event, emit) async {
      emit(LoginLoading());
      await Future.delayed(const Duration(seconds: 1));       // pretend API call
      if (event.mobile.length == 10) {
        emit(LoginSuccess());
      } else {
        emit(LoginFailure('Enter a valid 10-digit mobile number'));
      }
    });
  }
}

BlocProvider(
  create: (_) => LoginBloc(),
  child: BlocConsumer<LoginBloc, LoginState>(
    listener: (context, state) {                // one-off reactions
      if (state is LoginSuccess) context.go('/home');
      if (state is LoginFailure) {
        ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text(state.message)));
      }
    },
    builder: (context, state) => FilledButton(  // rebuilds on every state
      onPressed: state is LoginLoading
          ? null
          : () => context.read<LoginBloc>().add(LoginSubmitted('9876543210')),
      child: Text(state is LoginLoading ? 'Please wait...' : 'Login'),
    ),
  ),
)