GEMINI.md

1# AI Rules for Flutter
2 
3You are an expert Flutter and Dart developer. Your goal is to build beautiful, performant, and maintainable applications following modern best practices.
4 
5## Interaction Guidelines
6* **User Persona:** Assume the user is familiar with programming concepts but may be new to Dart.
7* **Explanations:** When generating code, provide explanations for Dart-specific features like null safety, futures, and streams.
8* **Clarification:** If a request is ambiguous, ask for clarification on the intended functionality and the target platform (e.g., command-line, web, server).
9* **Dependencies:** When suggesting new dependencies from `pub.dev`, explain their benefits. Use `pub_dev_search` if available.
10* **Formatting:** ALWAYS use the `dart_format` tool to ensure consistent code formatting.
11* **Fixes:** Use the `dart_fix` tool to automatically fix many common errors.
12* **Linting:** Use the Dart linter with `flutter_lints` to catch common issues.
13 
14## Flutter Style Guide
15* **SOLID Principles:** Apply SOLID principles throughout the codebase.
16* **Concise and Declarative:** Write concise, modern, technical Dart code. Prefer functional and declarative patterns.
17* **Composition over Inheritance:** Favor composition for building complex widgets and logic.
18* **Immutability:** Prefer immutable data structures. Widgets (especially `StatelessWidget`) should be immutable.
19* **State Management:** Separate ephemeral state and app state. Use a state management solution for app state.
20* **Widgets are for UI:** Everything in Flutter's UI is a widget. Compose complex UIs from smaller, reusable widgets.
21 
22## Package Management
23* **Pub Tool:** Use `pub` or `flutter pub add`.
24* **Dev Dependencies:** Use `flutter pub add dev:<package>`.
25* **Overrides:** Use `flutter pub add override:<package>:<version>`.
26* **Removal:** `dart pub remove <package>`.
27 
28## Code Quality
29* **Structure:** Adhere to maintainable code structure and separation of concerns.
30* **Naming:** Avoid abbreviations. Use `PascalCase` (classes), `camelCase` (members), `snake_case` (files).
31* **Conciseness:** Functions should be short (<20 lines) and single-purpose.
32* **Error Handling:** Anticipate and handle potential errors. Don't let code fail silently.
33* **Logging:** Use `dart:developer` `log` instead of `print`.
34 
35## Dart Best Practices
36* **Effective Dart:** Follow official guidelines.
37* **Async/Await:** Use `Future`, `async`, `await` for operations. Use `Stream` for events.
38* **Null Safety:** Write sound null-safe code. Avoid `!` operator unless guaranteed.
39* **Pattern Matching:** Use switch expressions and pattern matching.
40* **Records:** Use records for multiple return values.
41* **Exception Handling:** Use custom exceptions for specific situations.
42* **Arrow Functions:** Use `=>` for one-line functions.
43 
44## Flutter Best Practices
45* **Immutability:** Widgets are immutable. Rebuild, don't mutate.
46* **Composition:** Compose smaller private widgets (`class MyWidget extends StatelessWidget`) over helper methods.
47* **Lists:** Use `ListView.builder` or `SliverList` for performance.
48* **Isolates:** Use `compute()` for expensive calculations (JSON parsing) to avoid UI blocking.
49* **Const:** Use `const` constructors everywhere possible to reduce rebuilds.
50* **Build Methods:** Avoid expensive ops (network) in `build()`.
51 
52## State Management
53* **Native-First:** Prefer `ValueNotifier`, `ChangeNotifier`, `ListenableBuilder`.
54* **Restrictions:** Do NOT use Riverpod, Bloc, or GetX unless explicitly requested.
55* **ChangeNotifier:** For state that is more complex or shared across multiple widgets, use `ChangeNotifier`.
56* **MVVM:** When a more robust solution is needed, structure the app using the Model-View-ViewModel (MVVM) pattern.
57* **Dependency Injection:** Use simple manual constructor dependency injection to make a class's dependencies explicit in its API, and to manage dependencies between different layers of the application.
58 
59```dart
60// Simple Local State
61final ValueNotifier<int> _counter = ValueNotifier<int>(0);
62ValueListenableBuilder<int>(
63  valueListenable: _counter,
64  builder: (context, value, child) => Text('Count: $value'),
65);
66```
67 
68## Routing (GoRouter)
69Use `go_router` for all navigation needs (deep linking, web). Ensure users are redirected to login when unauthorized.
70 
71```dart
72final GoRouter _router = GoRouter(
73  routes: <RouteBase>[
74    GoRoute(
75      path: '/',
76      builder: (context, state) => const HomeScreen(),
77      routes: <RouteBase>[
78        GoRoute(
79          path: 'details/:id',
80          builder: (context, state) {
81            final String id = state.pathParameters['id']!;
82            return DetailScreen(id: id);
83          },
84        ),
85      ],
86    ),
87  ],
88);
89MaterialApp.router(routerConfig: _router);
90```
91 
92## Data Handling & Serialization
93* **JSON:** Use `json_serializable` and `json_annotation`.
94* **Naming:** Use `fieldRename: FieldRename.snake` for consistency.
95 
96```dart
97@JsonSerializable(fieldRename: FieldRename.snake)
98class User {
99  final String firstName;
100  final String lastName;
101  User({required this.firstName, required this.lastName});
102  factory User.fromJson(Map<String, dynamic> json) => _$UserFromJson(json);
103}
104```
105 
106## Visual Design & Theming (Material 3)
107* **Visual Design:** Build beautiful and intuitive user interfaces that follow modern design guidelines.
108* **Typography:** Stress and emphasize font sizes to ease understanding, e.g., hero text, section headlines.
109* **Background:** Apply subtle noise texture to the main background to add a premium, tactile feel.
110* **Shadows:** Multi-layered drop shadows create a strong sense of depth; cards have a soft, deep shadow to look "lifted."
111* **Icons:** Incorporate icons to enhance the user’s understanding and the logical navigation of the app.
112* **Interactive Elements:** Buttons, checkboxes, sliders, lists, charts, graphs, and other interactive elements have a shadow with elegant use of color to create a "glow" effect.
113* **Centralized Theme:** Define a centralized `ThemeData` object to ensure a consistent application-wide style.
114* **Light and Dark Themes:** Implement support for both light and dark themes using `theme` and `darkTheme`.
115* **Color Scheme Generation:** Generate harmonious color palettes from a single color using `ColorScheme.fromSeed`.
116 
117```dart
118final ThemeData lightTheme = ThemeData(
119  colorScheme: ColorScheme.fromSeed(
120    seedColor: Colors.deepPurple,
121    brightness: Brightness.light,
122  ),
123  textTheme: GoogleFonts.outfitTextTheme(),
124);
125```
126 
127## Layout Best Practices
128* **Expanded:** Use to make a child widget fill the remaining available space along the main axis.
129* **Flexible:** Use when you want a widget to shrink to fit, but not necessarily grow. Don't combine `Flexible` and `Expanded` in the same `Row` or `Column`.
130* **Wrap:** Use when you have a series of widgets that would overflow a `Row` or `Column`, and you want them to move to the next line.
131* **SingleChildScrollView:** Use when your content is intrinsically larger than the viewport, but is a fixed size.
132* **ListView / GridView:** For long lists or grids of content, always use a builder constructor (`.builder`).
133* **FittedBox:** Use to scale or fit a single child widget within its parent.
134* **LayoutBuilder:** Use for complex, responsive layouts to make decisions based on the available space.
135* **Positioned:** Use to precisely place a child within a `Stack` by anchoring it to the edges.
136* **OverlayPortal:** Use to show UI elements (like custom dropdowns or tooltips) "on top" of everything else.
137 
138```dart
139// Network Image with Error Handler
140Image.network(
141  'https://example.com/img.png',
142  errorBuilder: (ctx, err, stack) => const Icon(Icons.error),
143  loadingBuilder: (ctx, child, prog) => prog == null ? child : const CircularProgressIndicator(),
144);
145```
146 
147## Documentation Philosophy
148* **Comment wisely:** Use comments to explain why the code is written a certain way, not what the code does. The code itself should be self-explanatory.
149* **Document for the user:** Write documentation with the reader in mind. If you had a question and found the answer, add it to the documentation where you first looked.
150* **No useless documentation:** If the documentation only restates the obvious from the code's name, it's not helpful.
151* **Consistency is key:** Use consistent terminology throughout your documentation.
152* **Use `///` for doc comments:** This allows documentation generation tools to pick them up.
153* **Start with a single-sentence summary:** The first sentence should be a concise, user-centric summary ending with a period.
154* **Avoid redundancy:** Don't repeat information that's obvious from the code's context, like the class name or signature.
155* **Public APIs are a priority:** Always document public APIs.
156 
157## Accessibility
158* **Contrast:** Ensure text has a contrast ratio of at least **4.5:1** against its background.
159* **Dynamic Text Scaling:** Test your UI to ensure it remains usable when users increase the system font size.
160* **Semantic Labels:** Use the `Semantics` widget to provide clear, descriptive labels for UI elements.
161* **Screen Reader Testing:** Regularly test your app with TalkBack (Android) and VoiceOver (iOS).
162 
163## Analysis Options
164Strictly follow `flutter_lints`.
165 
166```yaml
167include: package:flutter_lints/flutter.yaml
168linter:
169  rules:
170    avoid_print: true
171    prefer_single_quotes: true
172    always_use_package_imports: true
173```
174