create promocode page

lib/presentation/viewmodel/promo_code_bloc.dart

@@ -0,0 +1,37 @@
+import 'package:flutter_bloc/flutter_bloc.dart';
+import '../../domain/usecase/apply_promo_code_usecase.dart';
+import '../event/promo_code_event.dart';
+import '../state/promo_code_state.dart';
+
+class PromoCodeBloc extends Bloc<PromoCodeEvent, PromoCodeState> {
+  final ApplyPromoCodeUsecase _applyPromoCodeUsecase;
+
+  PromoCodeBloc(this._applyPromoCodeUsecase) : super(const PromoCodeState()) {
+    on<PromoCodeApplyRequested>(_onApplyRequested);
+    on<PromoCodeReset>(_onReset);
+  }
+
+  Future<void> _onApplyRequested(
+      PromoCodeApplyRequested event,
+      Emitter<PromoCodeState> emit,
+      ) async {
+    emit(state.copyWith(status: PromoCodeStatus.loading));
+
+    try {
+      final result = await _applyPromoCodeUsecase(event.code);
+      emit(state.copyWith(
+        status: PromoCodeStatus.success,
+        newBalance: result.balance,
+      ));
+    } catch (e) {
+      emit(state.copyWith(
+        status: PromoCodeStatus.failure,
+        errorMessage: e.toString(),
+      ));
+    }
+  }
+
+  void _onReset(PromoCodeReset event, Emitter<PromoCodeState> emit) {
+    emit(const PromoCodeState());
+  }
+}