# GoRouter Navigation Setup - Complete Guide

This document explains the complete navigation setup for the warehouse management app using GoRouter with authentication-based redirects.

## Files Created/Modified

### New Files
1. **`/lib/core/router/app_router.dart`** - Main router configuration
2. **`/lib/core/router/README.md`** - Detailed router documentation
3. **`/lib/features/warehouse/presentation/pages/warehouse_selection_page_example.dart`** - Integration examples

### Modified Files
1. **`/lib/main.dart`** - Updated to use new router provider
2. **`/lib/features/operation/presentation/pages/operation_selection_page.dart`** - Updated navigation

## Architecture Overview

### Route Structure
```
/login              → LoginPage
/warehouses         → WarehouseSelectionPage
/operations         → OperationSelectionPage (requires warehouse)
/products           → ProductsPage (requires warehouse + operationType)
```

### Navigation Flow
```
┌─────────┐     ┌────────────┐     ┌────────────┐     ┌──────────┐
│  Login  │ --> │ Warehouses │ --> │ Operations │ --> │ Products │
└─────────┘     └────────────┘     └────────────┘     └──────────┘
     │                 │                  │                  │
     └─────────────────┴──────────────────┴──────────────────┘
                    Protected Routes
           (Require Authentication via SecureStorage)
```

## Key Features

### 1. Authentication-Based Redirects
- **Unauthenticated users** → Redirected to `/login`
- **Authenticated users on /login** → Redirected to `/warehouses`
- Uses `SecureStorage.isAuthenticated()` to check access token

### 2. Type-Safe Navigation
Extension methods provide type-safe navigation:
```dart
// Type-safe with auto-completion
context.goToOperations(warehouse);
context.goToProducts(warehouse: warehouse, operationType: 'import');

// vs. error-prone manual navigation
context.go('/operations', extra: warehouse); // Less safe
```

### 3. Parameter Validation
Routes validate required parameters and redirect on error:
```dart
final warehouse = state.extra as WarehouseEntity?;
if (warehouse == null) {
  // Show error and redirect to safe page
  return _ErrorScreen(message: 'Warehouse data is required');
}
```

### 4. Reactive Navigation
Router automatically reacts to authentication state changes:
```dart
// Login → Router detects auth change → Redirects to /warehouses
await ref.read(authProvider.notifier).login(username, password);

// Logout → Router detects auth change → Redirects to /login
await ref.read(authProvider.notifier).logout();
```

## Usage Guide

### Basic Navigation

#### 1. Navigate to Login
```dart
context.goToLogin();
```

#### 2. Navigate to Warehouses
```dart
context.goToWarehouses();
```

#### 3. Navigate to Operations with Warehouse
```dart
// From warehouse selection page
void onWarehouseSelected(WarehouseEntity warehouse) {
  context.goToOperations(warehouse);
}
```

#### 4. Navigate to Products with Warehouse and Operation
```dart
// From operation selection page
void onOperationSelected(WarehouseEntity warehouse, String operationType) {
  context.goToProducts(
    warehouse: warehouse,
    operationType: operationType, // 'import' or 'export'
  );
}
```

### Complete Integration Example

#### Warehouse Selection Page
```dart
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:minhthu/core/router/app_router.dart';
import 'package:minhthu/features/warehouse/domain/entities/warehouse_entity.dart';

class WarehouseSelectionPage extends ConsumerWidget {
  const WarehouseSelectionPage({super.key});

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    // Watch warehouse state
    final state = ref.watch(warehouseProvider);

    return Scaffold(
      appBar: AppBar(
        title: const Text('Select Warehouse'),
        actions: [
          IconButton(
            icon: const Icon(Icons.logout),
            onPressed: () async {
              // Logout - router will auto-redirect to login
              await ref.read(authProvider.notifier).logout();
            },
          ),
        ],
      ),
      body: ListView.builder(
        itemCount: state.warehouses.length,
        itemBuilder: (context, index) {
          final warehouse = state.warehouses[index];
          return ListTile(
            title: Text(warehouse.name),
            subtitle: Text(warehouse.code),
            onTap: () {
              // Type-safe navigation to operations
              context.goToOperations(warehouse);
            },
          );
        },
      ),
    );
  }
}
```

#### Operation Selection Page
```dart
import 'package:flutter/material.dart';
import 'package:minhthu/core/router/app_router.dart';
import 'package:minhthu/features/warehouse/domain/entities/warehouse_entity.dart';

class OperationSelectionPage extends StatelessWidget {
  final WarehouseEntity warehouse;

  const OperationSelectionPage({required this.warehouse});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(warehouse.name)),
      body: Column(
        children: [
          ElevatedButton(
            onPressed: () {
              // Navigate to products with import operation
              context.goToProducts(
                warehouse: warehouse,
                operationType: 'import',
              );
            },
            child: const Text('Import Products'),
          ),
          ElevatedButton(
            onPressed: () {
              // Navigate to products with export operation
              context.goToProducts(
                warehouse: warehouse,
                operationType: 'export',
              );
            },
            child: const Text('Export Products'),
          ),
        ],
      ),
    );
  }
}
```

## Authentication Integration

### How It Works

1. **App Starts**
   - Router checks `SecureStorage.isAuthenticated()`
   - If no token → Redirects to `/login`
   - If token exists → Allows navigation

2. **User Logs In**
   ```dart
   // AuthNotifier saves token and updates state
   await loginUseCase(request); // Saves to SecureStorage
   state = AuthState.authenticated(user);

   // GoRouterRefreshStream detects auth state change
   ref.listen(authProvider, (_, __) => notifyListeners());

   // Router re-evaluates redirect logic
   // User is now authenticated → Redirects to /warehouses
   ```

3. **User Logs Out**
   ```dart
   // AuthNotifier clears token and resets state
   await secureStorage.clearAll();
   state = const AuthState.initial();

   // Router detects auth state change
   // User is no longer authenticated → Redirects to /login
   ```

### SecureStorage Methods Used
```dart
// Check authentication
Future<bool> isAuthenticated() async {
  final token = await getAccessToken();
  return token != null && token.isNotEmpty;
}

// Save tokens (during login)
Future<void> saveAccessToken(String token);
Future<void> saveRefreshToken(String token);

// Clear tokens (during logout)
Future<void> clearAll();
```

## Error Handling

### 1. Missing Route Parameters
If required parameters are missing, user sees error and gets redirected:
```dart
GoRoute(
  path: '/operations',
  builder: (context, state) {
    final warehouse = state.extra as WarehouseEntity?;

    if (warehouse == null) {
      // Show error screen and redirect after frame
      WidgetsBinding.instance.addPostFrameCallback((_) {
        context.go('/warehouses');
      });
      return const _ErrorScreen(
        message: 'Warehouse data is required',
      );
    }

    return OperationSelectionPage(warehouse: warehouse);
  },
)
```

### 2. Page Not Found
Custom 404 page with navigation back to login:
```dart
errorBuilder: (context, state) {
  return Scaffold(
    body: Center(
      child: Column(
        children: [
          Icon(Icons.error_outline, size: 64),
          Text('Page "${state.uri.path}" does not exist'),
          ElevatedButton(
            onPressed: () => context.go('/login'),
            child: const Text('Go to Login'),
          ),
        ],
      ),
    ),
  );
}
```

### 3. Authentication Errors
If `SecureStorage` throws an error, redirect to login for safety:
```dart
Future<String?> _handleRedirect(context, state) async {
  try {
    final isAuthenticated = await secureStorage.isAuthenticated();
    // ... redirect logic
  } catch (e) {
    debugPrint('Error in redirect: $e');
    return '/login'; // Safe fallback
  }
}
```

## Extension Methods Reference

### Path-Based Navigation
```dart
context.goToLogin();          // Go to /login
context.goToWarehouses();     // Go to /warehouses
context.goToOperations(warehouse);
context.goToProducts(warehouse: w, operationType: 'import');
context.goBack();             // Pop current route
```

### Named Route Navigation
```dart
context.goToLoginNamed();
context.goToWarehousesNamed();
context.goToOperationsNamed(warehouse);
context.goToProductsNamed(warehouse: w, operationType: 'export');
```

## Testing Authentication Flow

### Test Case 1: Fresh Install
1. App starts → No token → Redirects to `/login`
2. User logs in → Token saved → Redirects to `/warehouses`
3. User selects warehouse → Navigates to `/operations`
4. User selects operation → Navigates to `/products`

### Test Case 2: Logged In User
1. App starts → Token exists → Shows `/warehouses`
2. User navigates normally through app
3. User logs out → Token cleared → Redirects to `/login`

### Test Case 3: Manual URL Entry
1. User tries to access `/products` directly
2. Router checks authentication
3. If not authenticated → Redirects to `/login`
4. If authenticated but missing params → Redirects to `/warehouses`

## Troubleshooting

### Problem: Stuck on login page after successful login
**Solution**: Check if token is being saved to SecureStorage
```dart
// In LoginUseCase
await secureStorage.saveAccessToken(user.accessToken);
```

### Problem: Redirect loop between login and warehouses
**Solution**: Verify `isAuthenticated()` logic
```dart
// Should return true only if token exists
Future<bool> isAuthenticated() async {
  final token = await getAccessToken();
  return token != null && token.isNotEmpty;
}
```

### Problem: Navigation parameters are null
**Solution**: Use extension methods with correct types
```dart
// Correct
context.goToOperations(warehouse);

// Wrong - may lose type information
context.go('/operations', extra: warehouse);
```

### Problem: Router doesn't react to auth changes
**Solution**: Verify GoRouterRefreshStream is listening
```dart
GoRouterRefreshStream(this.ref) {
  ref.listen(
    authProvider, // Must be the correct provider
    (_, __) => notifyListeners(),
  );
}
```

## Next Steps

1. **Implement Warehouse Provider**
   - Create warehouse state management
   - Load warehouses from API
   - Integrate with warehouse selection page

2. **Implement Products Provider**
   - Create products state management
   - Load products based on warehouse and operation
   - Integrate with products page

3. **Add Loading States**
   - Show loading indicators during navigation
   - Handle network errors gracefully

4. **Add Analytics**
   - Track navigation events
   - Monitor authentication flow

## Related Documentation

- **Router Details**: `/lib/core/router/README.md`
- **Auth Setup**: `/lib/features/auth/di/auth_dependency_injection.dart`
- **SecureStorage**: `/lib/core/storage/secure_storage.dart`
- **Examples**: `/lib/features/warehouse/presentation/pages/warehouse_selection_page_example.dart`

## Summary

The complete GoRouter setup provides:
- Authentication-based navigation with auto-redirect
- Type-safe parameter passing
- Reactive updates on auth state changes
- Proper error handling and validation
- Easy-to-use extension methods
- Integration with existing SecureStorage and Riverpod

The app flow is: **Login → Warehouses → Operations → Products**

All protected routes automatically redirect to login if user is not authenticated.