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Add as custom prompt to Roocode you can completely replace the system prompt for this mode (aside from the role definition and custom instructions) by creating a file at .roo/system-prompt-codershortrules in your workspace. You are Roo, a highly skilled software engineer with extensive knowledge in many programming languages, frameworks, design patterns, and best practices. Use tools one at a time to complete tasks step-by-step. Wait for user confirmation after each tool use. Tools read_file: Read file contents. Use for analyzing code, text files, or configs. Output includes line numbers. Extracts text from PDFs and DOCX. Not for other binary files. Parameters: path (required) search_files: Search files in a directory using regex. Shows matches with context. Useful for finding code patterns or specific content. Parameters: path (required), regex (required), file_pattern (optional) list_files: List files and directories. Can be recursive. Don’t use to check if files you created exist; user will confirm. Parameters: path (required), recursive (optional) list_code_definition_names: List top-level code definitions (classes, functions, etc.) in a directory. Helps understand codebase structure. Parameters: path (required) apply_diff: Replace code in a file using a search and replace block. Must match existing content exactly. Use read_file first if unsure. Parameters: path (required), diff (required), start_line (required), end_line (required) Diff Format: text Wrap Copy <<<<<<< SEARCH [exact content] ======= [new content] >>>>>>> REPLACE write_to_file: Write full content to a file. Overwrites if exists, creates if not. MUST provide COMPLETE file content, not partial updates. MUST include app 3 parameters, path, content, and line_count Parameters: path (required), content (required), line_count (required) execute_command: Run CLI commands. Explain what the command does. Prefer complex commands over scripts. Commands run in the current directory. To run in a different directory, use cd path && command. Parameters: command (required) ask_followup_question: Ask the user a question to get more information. Use when you need clarification or details. Parameters: question (required) attempt_completion: Present the task result to the user. Optionally provide a CLI command to demo the result. Don’t use it until previous tool uses are confirmed successful. Parameters: result (required), command (optional) Tool Use Formatting IMPORTANT REPLACE tool_name with the tool you want to use, for example read_file. IMPORTANT REPLACE parameter_name with the parameter name, for example path. Format tool use with XML tags, e.g.: text Wrap Copy value1 value2 Guidelines Choose the right tool for the task. Use one tool at a time. Format tool use correctly. Wait for user confirmation after each tool use. Don’t assume tool success; wait for user feedback. Rules pass correct paths to tools. Don’t use ~ or $HOME. Tailor commands to the user's system. Prefer other editing tools over write_to_file for changes. Provide complete file content when using write_to_file. Don’t ask unnecessary questions; use tools to get information. Don’t be conversational; be direct and technical. Consider environment_details for context. ALWAYS replace tool_name, parameter_name, and parameter_value with actual values. Objective Break task into steps. Use tools to accomplish each step. Wait for user confirmation after each tool use. Use attempt_completion when task is complete.

# Angular v19+ Development Standards and Best Practices: A Comprehensive Guide ## 1. Core Architecture Guidelines We follow these core architectural patterns: - **Standalone Components:** All components, directives, and pipes are standalone by default (Angular v19+) - **Strong Typing:** Implement proper TypeScript types, interfaces, and models throughout the codebase - **Single Responsibility Principle (SRP):** Each component and service should have a single, well-defined responsibility - **Rule of One:** Keep files focused on a single concept or functionality - **Reactive State Management:** Use Signals for reactive and efficient state management - **Dependency Injection:** Utilize Angular's DI system for service management - **Lazy Loading:** Implement Deferrable Views and route-level lazy loading with `loadComponent` - **Directive Composition:** Use the Directive Composition API for reusable component behavior ## 2. Angular Style Guide Compliance Following the official Angular Style Guide: - **Code Size:** Limit files to 400 lines of code - **Single Purpose Files:** Define one entity (component, service, etc.) per file - **Naming Conventions:** Use consistent, descriptive names for all symbols - **Folder Structure:** Organize by feature-based folders - **File Separation:** Extract templates and styles to their own files for components - **Property Decoration:** Properly decorate input and output properties - **Component Selectors:** Use custom prefixes and kebab-case for component selectors (e.g., `app-feature-name`) ## 3. Input Signals For component inputs, follow these guidelines: - **Modern Signal-Based Inputs:** Use the `input()` function instead of `@Input()` decorator: ```typescript // Preferred value = input(0); // Creates InputSignal // Instead of @Input() value = 0; ``` - **Required Inputs:** Use `input.required()` for mandatory inputs: ```typescript value = input.required<number>(); ``` - **Input Transformations:** Apply transformations when needed: ```typescript disabled = input(false, { transform: booleanAttribute }); value = input(0, { transform: numberAttribute }); ``` - **Two-Way Binding:** Use model inputs for two-way binding: ```typescript value = model(0); // Creates a model input with change propagation // Update model values with .set() or .update() increment() { this.value.update(v => v + 1); } ``` - **Input Aliases:** Use aliases when necessary: ```typescript value = input(0, { alias: "sliderValue" }); ``` ## 4. Component Development When creating components: - **Naming Pattern:** Use consistent naming - `feature.type.ts` (e.g., `hero-list.component.ts`) - **Template Extraction:** Use separate `.html` files for non-trivial templates - **Style Extraction:** Place styles in separate `.css/.scss` files - **Signal-Based Inputs:** Use `input()` function for component inputs - **Two-Way Binding:** Use `model()` function for two-way binding - **Lifecycle Hooks:** Implement appropriate lifecycle hook interfaces (OnInit, OnDestroy, etc.) - **Element Selectors:** Keep components as elements (`selector: 'app-hero-detail'`) - **Logic Delegation:** Move complex logic to services - **Input Initialization:** Provide default values or mark as required - **Lazy Loading:** Use `@defer` for heavy components or features - **Error Handling:** Implement proper error boundaries with try-catch blocks - **Modern Control Flow:** Use `@if`, `@for`, `@switch` instead of structural directives - **State Representation:** Implement proper loading and error states - **Derived State:** Use `computed()` for derived state calculations ## 5. Styling Standards Our styling conventions: - **Component Encapsulation:** Use component-specific styles with proper encapsulation - **CSS Methodology:** Follow BEM methodology for CSS class naming when not using Angular Material - **Component Libraries:** Use Angular Material or other component libraries consistently - **Theming:** Implement proper theming and color systems - **Accessibility:** Follow a11y standards in all components - **Dark Mode:** Support dark mode where appropriate ## 6. Services and Dependency Injection For services and DI: - **Service Declaration:** Use `@Injectable()` decorator with `providedIn: 'root'` for singleton services - **Data Services:** Make data services responsible for API calls and data operations - **Error Handling:** Implement proper error handling in services - **DI Hierarchy:** Follow the Angular DI hierarchy appropriately - **Service Contracts:** Use interfaces to define service contracts - **Focused Responsibilities:** Keep services focused on specific tasks ## 7. Directives and Pipes When creating directives and pipes: - **Attribute Directives:** Use for presentation logic without templates - **Host Property:** Use the `host` property for bindings and listeners: ```typescript @Directive({ standalone: true, selector: '[appHighlight]', host: { // Host bindings '[class.highlighted]': 'isHighlighted', '[style.color]': 'highlightColor', // Host listeners '(click)': 'onClick($event)', '(mouseenter)': 'onMouseEnter()', '(mouseleave)': 'onMouseLeave()', // Static properties 'role': 'button', '[attr.aria-label]': 'ariaLabel' } }) ``` - **Selector Prefixes:** Use custom prefixes for directive selectors - **Pure Pipes:** Make pipes pure when possible for better performance - **Pipe Naming:** Follow naming conventions for pipes (camelCase) ## 8. State Management For state management: - **Signals:** Use Signals as the primary state management solution - **Component Inputs:** Use signal inputs with `input()` for component inputs - **Two-Way Binding:** Use model inputs with `model()` for two-way binding - **Local State:** Use writable signals with `signal()` for local component state - **Derived State:** Use computed signals with `computed()` for derived state - **Side Effects:** Use `effect()` for handling side effects - **Error Handling:** Implement proper error handling in signal computations - **Signal Conversion:** Use `toSignal()` and `toObservable()` for interoperability with RxJS ## 9. Testing Standards For testing: - **Test Coverage:** Maintain high test coverage for all components and services - **Unit Tests:** Write focused unit tests for services, pipes, and components - **Component Testing:** Test components with TestBed and component harnesses - **Mocking:** Use proper mocking techniques for dependencies - **Test Organization:** Follow AAA pattern (Arrange, Act, Assert) for test organization - **Test Naming:** Use descriptive test names that explain the expected behavior ## 10. Performance Optimization For optimal performance: - **Change Detection:** Use OnPush change detection strategy for components - **Lazy Loading:** Implement lazy loading for routes and components - **Virtual Scrolling:** Use virtual scrolling for long lists - **Memoization:** Memoize expensive computations - **Bundle Size:** Monitor and optimize bundle size - **Server-Side Rendering:** Implement SSR for improved initial load performance - **Web Workers:** Offload intensive operations to web workers when appropriate ## 11. Security Practices Security best practices: - **XSS Prevention:** Always sanitize user input - **CSRF Protection:** Implement CSRF tokens for forms - **Content Security Policy:** Use appropriate CSP headers - **Authentication:** Implement secure authentication practices - **Authorization:** Use proper authorization checks - **Sensitive Data:** Never expose sensitive data in client-side code ## 12. Accessibility Standards Accessibility requirements: - **ARIA Attributes:** Use appropriate ARIA attributes - **Keyboard Navigation:** Ensure all interactive elements are keyboard accessible - **Color Contrast:** Maintain proper color contrast ratios - **Screen Readers:** Test with screen readers - **Focus Management:** Implement proper focus management - **Alternative Text:** Provide alt text for images ## 13. Documentation Documentation standards: - **Code Comments:** Use JSDoc comments for public APIs - **README Files:** Maintain up-to-date README files for projects and major features - **API Documentation:** Document public APIs thoroughly - **Changelog:** Maintain a changelog for version updates - **Usage Examples:** Provide usage examples for components and services

# NgRx Signals Guidelines This document outlines best practices for state management in our Angular applications using NgRx Signals Store. ## 1. NgRx Signals Architecture Principles - **Component-Centric Design:** Design stores around component requirements - **Hierarchical State:** Organize state in a hierarchical structure when needed - **Computed State:** Derive state using computed values - **Declarative Updates:** Use declarative state updates with patchState - **Store Composition:** Compose stores using features and providers - **Reactivity First:** Build reactive UIs with automatic change detection - **Signal Interoperability:** Ensure signals work with existing RxJS-based systems ## 2. Signal Store Setup - **Store Creation:** Use the `signalStore` function to create stores. - **Protected State:** By default (`{ protectedState: true }`), Signal Store state cannot be mutated from the outside using `patchState`. This enforces encapsulation and ensures state changes occur only through defined methods. For flexibility, you can allow external mutations by setting `{ protectedState: false }`. - **State Definition:** Define the initial state shape using `withState({...})`. **Crucially, the root level of the state provided to `withState` must be an object (record/dictionary), not an array.** - **Correct:** `withState({ users: [], count: 0 })`, `withState({})` - **Incorrect:** `withState([])`, `withState([])` - **Dependency Injection:** Make stores injectable using `{ providedIn: 'root' }` or feature/component providers. - **Store Composition:** Compose stores using the feature-based composition pattern (see Advanced Patterns). - **Store Features:** Use built-in (`withEntities`, `withHooks`) or custom signal store features for cross-cutting concerns. - **State Interface:** Define clear state interfaces for strong typing. - **Private/Internal State, Computed Properties, Props, and Methods:** Prefix internal or private state properties, computed signals, props, and methods with an underscore (`_`). This convention clarifies their intended usage and helps prevent accidental access from outside the store. - **Example:** ```typescript withState({ count: 0, _internalCount: 0 }); withComputed(({ count, _internalCount }) =&gt; ({ doubleCount: computed(() =&gt; count() * 2), _doubleInternal: computed(() =&gt; _internalCount() * 2), })); withProps(({ _internalCount }) =&gt; ({ _internalCount$: toObservable(_internalCount), })); withMethods(store =&gt; ({ increment: () =&gt; patchState(store, { count: store.count() + 1 }), _incrementInternal: () =&gt; patchState(store, { _internalCount: store._internalCount() + 1 }), })); ``` - **Integrity of Store Members:** Avoid overriding store members (e.g., defining a method or computed signal with the same name as a state slice). - **Initialization:** Initialize state with meaningful defaults within `withState`. - **Collection Management:** Use `withEntities` for efficient collection management. ```typescript // Signal store setup example import { signalStore, withState, withComputed, withMethods, patchState, withEntities } from '@ngrx/signals'; import { entityConfig, EntityState } from '@ngrx/signals/entities'; import { computed, inject } from '@angular/core'; import { UserService } from './user.service'; import { User } from './user.model'; import { setAllEntities } from '@ngrx/signals/entities'; import { firstValueFrom } from 'rxjs'; export interface UserState { selectedUserId: string | null; loading: boolean; error: string | null; } const initialState: UserState = { selectedUserId: null, loading: false, error: null, }; export const UserStore = signalStore( { providedIn: 'root' }, withState(initialState), withEntities(), withComputed(({ entities, selectedUserId }) =&gt; ({ selectedUser: computed(() =&gt; { const id = selectedUserId(); return id ? entities()[id] : undefined; }), totalUserCount: computed(() =&gt; entities().length), })), withMethods((store, userService = inject(UserService)) =&gt; ({ async loadUsers(): Promise { patchState(store, { loading: true, error: null }); try { const users = await firstValueFrom(userService.getUsers()); patchState(store, setAllEntities(users), { loading: false }); } catch (e) { patchState(store, { loading: false, error: 'Failed to load users' }); } }, selectUser(userId: string | null): void { patchState(store, { selectedUserId: userId }); }, })), ); ``` ## 3. Signal Store Methods - **Method Definition:** Define methods within `withMethods`. - **Dependency Injection:** Use `inject()` within the `withMethods` factory function to access services. For dependencies shared across multiple store features (methods, computed, hooks), consider grouping them using `withProps` for better organization (see Section 7). - **Method Organization:** Group methods by domain functionality. - **Method Naming:** Use clear, action-oriented names. - **State Updates:** Use `patchState(store, newStateSlice)` or `patchState(store, (currentState) =&gt; newStateSlice)` for updating state immutably. - **Async Operations:** Handle async operations within methods, updating loading/error states appropriately using `patchState`. Consider `rxMethod` for complex RxJS flows or `signalMethod` for simpler signal-based side effects (see Section 6). - **Computed Properties:** Define derived state using `withComputed`. Access state slices directly within the factory function. - **RxJS Integration:** Prefer `rxMethod` for integrating RxJS streams declaratively (see Section 6). ```typescript // Signal store method examples using patchState and inject import { signalStore, withState, withMethods, patchState } from '@ngrx/signals'; import { inject } from '@angular/core'; import { TodoService } from './todo.service'; import { Todo } from './todo.model'; export interface TodoState { todos: Todo[]; loading: boolean; } export const TodoStore = signalStore( { providedIn: 'root' }, withState({ todos: [], loading: false }), withMethods((store, todoService = inject(TodoService)) =&gt; ({ addTodo(todo: Todo): void { patchState(store, state =&gt; ({ todos: [...state.todos, todo], })); }, async loadTodosSimple(): Promise { patchState(store, { loading: true }); try { const todos = await firstValueFrom(todoService.getTodos()); patchState(store, { todos, loading: false }); } catch (error) { patchState(store, { loading: false }); } }, })), ); ``` ## 4. Entities in Signal Store - **Entity Configuration:** Configure entities with proper ID selectors - **Collection Operations:** Use entity operations for CRUD operations - **Entity Relationships:** Handle entity relationships with proper computed properties - **Entity Updates:** Prefer atomic entity updates over bulk state updates ```typescript // Entity configuration and operations const userEntityConfig = entityConfig({ collection: 'users', selectId: (user: User) =&gt; user.id, }); export const UserStore = signalStore( withEntities(userEntityConfig), withMethods(store =&gt; ({ addUser: signalMethod(user =&gt; { patchState(store, addEntity(user)); }), updateUser: signalMethod&lt;{ id: string; changes: Partial }&gt;(({ id, changes }) =&gt; { patchState(store, updateEntity({ id, changes })); }), removeUser: signalMethod(id =&gt; { patchState(store, removeEntity(id)); }), setUsers: signalMethod(users =&gt; { patchState(store, setAllEntities(users)); }), })), ); ``` ## 5. Component Integration ### Component State Access - **Signal Properties:** Access signals directly in component templates - **OnPush Strategy:** Use OnPush change detection with signal-based components - **Store Injection:** Inject store services using the `inject` function - **Default Values:** Provide default values for all signals - **Computed Values:** Derive computed values from signals - **Signal Effects:** Use component effects for side effects ```typescript // Signal Store component integration @Component({ standalone: true, imports: [UserListComponent], template: ` @if (userStore.users().length &gt; 0) { } @else { <p>No users loaded yet.</p> } Selected user: {{ selectedUserName() }} `, changeDetection: ChangeDetectionStrategy.OnPush, }) export class UsersContainerComponent implements OnInit { readonly userStore = inject(UserStore); selectedUserName = computed(() =&gt; { const user = this.userStore.selectedUser(); return user ? user.name : 'None'; }); constructor() { effect(() =&gt; { const userId = this.userStore.selectedUserId(); if (userId) { console.log(`User selected: ${userId}`); } }); } ngOnInit() { this.userStore.loadUsers(); } } ``` ### Signal Store Hooks - **Using Hooks:** Leverage `withHooks` to add lifecycle hooks to stores - **Initialization:** Use `onInit` for store initialization - **Cleanup:** Use `onDestroy` for cleaning up resources - **State Synchronization:** Use hooks to synchronize state between stores ```typescript // Signal store with hooks export const UserStore = signalStore( withState({ /* initial state */ }), withMethods(/* store methods */), withHooks({ onInit: store =&gt; { // Initialize the store store.loadUsers(); // Return cleanup function if needed return () =&gt; { // Cleanup code }; }, }), ); ``` ## 6. Advanced Signal Patterns ### Signal Store Features - **Feature Creation:** Create reusable features with `signalStoreFeature`. - **Generic Feature Types:** When creating custom features that accept input or need to work with variable types, define them using generic type parameters (e.g., ``) for better type safety and reusability. - **Correct:** `function withMyFeature(config: Config) { return signalStoreFeature(/*...*/); }` - **Incorrect:** `function withMyFeature(config: Config) { return signalStoreFeature(/*...*/); }` - **Feature Composition:** Compose multiple features together. - **Cross-Cutting Concerns:** Use features for cross-cutting concerns like logging or undo/redo. - **State Slices:** Use features to define and manage specific slices of state. ```typescript // Signal store feature export function withUserFeature() { return signalStoreFeature( withState({ /* feature state */ }), withComputed(state =&gt; ({ /* computed properties */ })), withMethods(store =&gt; ({ /* methods */ })), ); } // Using the feature export const AppStore = signalStore( withUserFeature(), withOtherFeature(), withMethods(store =&gt; ({ /* app-level methods */ })), ); ``` ### Signals and RxJS Integration - **Signal Conversion:** Use `toSignal()` (from `@angular/core/rxjs-interop`) and `toObservable()` (from `@angular/core`) for interoperability between Signals and Observables when needed (e.g., integrating with non-signal-based parts of the app or older NgRx Store). - **Effects with Signals:** Use Angular's `effect()` for reactions to signal changes within components or services. Avoid complex logic inside `effect()`; delegate to store methods. - **`rxMethod` for Store Operations:** Use `rxMethod(pipeline)` provided by `@ngrx/signals/rxjs-interop` to handle Observable-based side effects declaratively within `withMethods`. It simplifies managing subscriptions and integrating RxJS operators directly into the store's workflow. - Accepts input values, Observables, or Signals. - Automatically manages the subscription lifecycle. - **Reactive Patterns:** Combine signals with RxJS using `rxMethod` for complex asynchronous operations, debouncing, switching, etc., keeping the reactive logic encapsulated within the store. ```typescript // Signal and RxJS integration using rxMethod import { signalStore, withState, withMethods, patchState } from '@ngrx/signals'; import { rxMethod } from '@ngrx/signals/rxjs-interop'; import { tapResponse } from '@ngrx/operators'; import { pipe, switchMap, tap } from 'rxjs/operators'; import { EMPTY, firstValueFrom } from 'rxjs'; import { inject } from '@angular/core'; import { HttpClient, HttpErrorResponse } from '@angular/common/http'; import { User } from './user.model'; export interface UserState { users: User[]; loading: boolean; error: string | null; } export const UserStore = signalStore( { providedIn: 'root' }, withState({ users: [], loading: false, error: null }), withMethods((store, http = inject(HttpClient)) =&gt; ({ loadUsers: rxMethod( pipe( switchMap(() =&gt; { patchState(store, { loading: true, error: null }); return http.get('/api/users').pipe( tapResponse({ next: users =&gt; patchState(store, { users, loading: false }), error: (error: HttpErrorResponse) =&gt; { patchState(store, { loading: false, error: 'Failed to load users' }); }, }), ); }), ), ), })), ); // --- Component Integration Example --- import { Component, inject, OnInit, ChangeDetectionStrategy } from '@angular/core'; import { Store } from '@ngrx/store'; import { selectAllUsers } from './legacy-selectors'; import { toSignal, toObservable } from '@angular/core/rxjs-interop'; import { UserStore } from './user.store'; @Component({ selector: 'app-user', template: ` @if (users().length &gt; 0) { Users: {{ users().length }} } @if (userStore.loading()) { Loading... } @if (userStore.error(); as errorMsg) { Error: {{ errorMsg }} } Reload Users <p>Legacy Users Count (from signal): {{ legacyUsers().length }}</p> User List <ul> @for (user of users(); track user.id) { <li>{{ user.name }}</li> } @empty { <li>No users found.</li> } </ul> `, changeDetection: ChangeDetectionStrategy.OnPush, }) export class UserComponent implements OnInit { readonly userStore = inject(UserStore); readonly users = this.userStore.users; readonly loading = this.userStore.loading; readonly error = this.userStore.error; private readonly legacyStore = inject(Store); readonly legacyUsers = toSignal(this.legacyStore.select(selectAllUsers), { initialValue: [] }); readonly users$ = toObservable(this.userStore.users); ngOnInit() { this.userStore.loadUsers(); this.users$.subscribe(users =&gt; console.log('Users Observable:', users)); } } ``` ### `signalMethod` for Signal-Based Side Effects `signalMethod` is a factory function useful for managing side effects driven by Angular Signals _within your Signal Store_, typically inside `withMethods`. It provides a way to react to signal changes without relying on RxJS, accepting a callback that performs the side effect and returning a processor function. This processor function can then be called with either a static value or a signal. When defined within `withMethods`, `signalMethod` offers several benefits: - **Input Flexibility:** The returned processor function accepts static values or Signals (e.g., signals from the store's state or signals passed in from a component) as input. - **Automatic Cleanup:** It uses an `effect` internally. Since `signalMethod` is typically created within the store's injection context (when defined in `withMethods`), the underlying `effect` is automatically cleaned up when the store is destroyed. - **Explicit Tracking:** Only the input signal passed directly to the processor function is tracked. Other signals used _inside_ the callback function are not tracked by this specific effect, preventing unintended triggers. - **Lightweight:** Offers a smaller bundle size compared to `rxMethod` as it avoids the RxJS dependency. ```typescript // Using signalMethod within withMethods import { signalStore, withState, withMethods, patchState } from '@ngrx/signals'; import { signalMethod } from '@ngrx/signals'; // Import signalMethod import { computed, inject, signal, Signal, WritableSignal, Injector } from '@angular/core'; import { Logger } from './logger'; // 1. Define the State Interface interface UserPreferencesState { theme: 'light' | 'dark'; sendNotifications: boolean; } // 2. Define the Initial State const initialState: UserPreferencesState = { theme: 'light', sendNotifications: true, }; export const PreferencesStore = signalStore( { providedIn: 'root' }, withState(initialState), withMethods((store, logger = inject(Logger), injector = inject(Injector)) =&gt; ({ setSendNotifications(enabled: boolean): void { patchState(store, { sendNotifications: enabled }); }, // 👇 Define signalMethod to react to theme changes (access theme via store.theme()) logThemeChange: signalMethod&lt;'light' | 'dark'&gt;(theme =&gt; { logger.log(`Theme changed to: ${theme}`); // Perform side effects like updating CSS variables or analytics }), // Method to update the theme state slice setTheme(newTheme: 'light' | 'dark'): void { patchState(store, { theme: newTheme }); }, // Method demonstrating passing an external signal trackExternalSignal: signalMethod( value =&gt; { logger.log(`External signal tracked in store: ${value}`); }, // Optional: Can explicitly provide injector if needed, though usually // inherited from withMethods context. // { injector }, ), })), ); // --- Component using the store --- import { Component, inject, signal } from '@angular/core'; import { PreferencesStore } from './preferences.store'; @Component({ /* ... */ template: ` <p>Current Theme: {{ store.theme() }}</p> Set Dark Theme Set Light Theme Update External `, }) export class SettingsComponent { readonly store = inject(PreferencesStore); readonly external = signal('initial'); constructor() { // 👇 Trigger the effect whenever the store's theme signal changes // Access the theme signal via the store instance this.store.logThemeChange(this.store.theme); // 👇 Trigger the effect whenever the external signal changes this.store.trackExternalSignal(this.external); // 👇 Call with a static value (runs the callback once) this.store.logThemeChange('light'); // Logs: "Theme changed to: light" } } ``` #### Cleanup Considerations When `signalMethod` is defined within `withMethods` (the standard approach in Signal Store), its underlying effect is tied to the store's lifecycle and cleaned up automatically. Manual cleanup (providing an injector when _calling_ the processor function) is generally only needed in advanced scenarios where you might be calling the processor function with a signal from a context that has a shorter lifespan than the store itself, which is less common for store methods. #### Comparison with `rxMethod` `signalMethod` serves a similar purpose to `rxMethod` but without RxJS. - **Choose `signalMethod` when:** - You need simple side effects reacting to signal changes. - You want to minimize bundle size and avoid an RxJS dependency for this specific task. - Advanced stream manipulation (debouncing, switching, merging, race condition handling) is not required. - **Choose `rxMethod` when:** - You need the power of RxJS operators (`debounceTime`, `switchMap`, `concatMap`, `tapResponse`, etc.). - You are managing complex asynchronous flows, ensuring order, or handling race conditions. - You are integrating with other RxJS-based parts of your application. Remember that Signals lack the built-in concurrency and complex stream management operators available in RxJS. For intricate asynchronous side effects, `rxMethod` often provides a more robust solution. ```typescript // Signal and RxJS integration using rxMethod (Existing Example) import { signalStore, withState, withMethods, patchState } from '@ngrx/signals'; import { rxMethod } from '@ngrx/signals/rxjs-interop'; // ... rest of rxMethod example ... ``` ## 7. Custom Store Properties and Exposing Observables - **Adding Static and Custom Properties:** Use the `withProps` feature to add static properties, observables, dependencies, or other custom properties to a SignalStore. The factory function receives state signals, previously defined properties, and methods, and returns an object with additional properties for the store. - **Exposing Observables for Backwards Compatibility:** To support integration with RxJS-based APIs or for backwards compatibility, expose state as observables using `toObservable` within `withProps`. - **Example: Exposing an Observable** ```typescript import { toObservable } from '@angular/core/rxjs-interop'; import { signalStore, withProps, withState } from '@ngrx/signals'; import { Book } from './book.model'; type BooksState = { books: Book[]; isLoading: boolean; }; export const BooksStore = signalStore( withState({ books: [], isLoading: false }), withProps(({ isLoading }) =&gt; ({ isLoading$: toObservable(isLoading), })), ); ``` - **Grouping Dependencies:** You can also use `withProps` to group dependencies (such as services or loggers) that are required across multiple store features, making them available to methods and hooks. - **Example: Grouping Dependencies** ```typescript import { inject } from '@angular/core'; import { signalStore, withProps, withState } from '@ngrx/signals'; import { Logger } from './logger'; import { Book } from './book.model'; import { BooksService } from './books.service'; type BooksState = { books: Book[]; isLoading: boolean; }; export const BooksStore = signalStore( withState({ books: [], isLoading: false }), withProps(() =&gt; ({ booksService: inject(BooksService), logger: inject(Logger), })), withMethods(({ booksService, logger, ...store }) =&gt; ({ async loadBooks(): Promise { logger.debug('Loading books...'); patchState(store, { isLoading: true }); const books = await booksService.getAll(); logger.debug('Books loaded successfully', books); patchState(store, { books, isLoading: false }); }, })), withHooks({ onInit({ logger }) { logger.debug('BooksStore initialized'); }, }), ); ``` ## 8. Testing Signal Store - **Test via the Public API:** Always interact with the Signal Store through its public API (methods, computed properties, and signals), just as a component or service would. Avoid accessing or asserting on private/internal properties or methods. - **Use TestBed:** Prefer using Angular's `TestBed` to instantiate and inject the Signal Store, as this ensures proper dependency injection and effect execution. This is especially important for stores using `inject`, `rxMethod`, or `withHooks`. - **Mock Dependencies:** When testing the store itself, mock its dependencies (e.g., services) to control their behavior and isolate the store logic. - **Mock the Store for Consumers:** When testing a component or service that uses a Signal Store, mock the store itself (using native mocks, spies, or libraries like ng-mocks or auto-spies). - **Test State and Computed Properties:** Assert on the values returned by public signals and computed properties, not on internal state. - **Test Methods and Async Flows:** Trigger public methods (including those using `rxMethod` or async logic) and assert on the resulting state or computed values. - **Use `unprotected` for Protected State:** If you need to patch protected state in tests, use the `unprotected` utility from `@ngrx/signals/testing`. - **Integration Testing:** For simple stores, consider integration tests that cover both the store and the component together. - **Test Custom Extensions:** Test custom store features/extensions either in combination with a store or in isolation using a wrapper Signal Store. ### Example: Testing a Globally Provided Store ```typescript import { MoviesStore } from './movies.store'; import { TestBed } from '@angular/core/testing'; describe('MoviesStore', () =&gt; { it('should verify that three movies are available', () =&gt; { const store = TestBed.inject(MoviesStore); expect(store.movies()).toHaveLength(3); }); }); ``` ### Example: Testing with Locally Provided Store ```typescript import { MoviesStore } from './movies.store'; import { TestBed } from '@angular/core/testing'; describe('MoviesStore', () =&gt; { it('should verify that three movies are available', () =&gt; { TestBed.configureTestingModule({ providers: [MoviesStore], }); const store = TestBed.inject(MoviesStore); expect(store.movies()).toHaveLength(3); }); }); ``` ### Example: Using `unprotected` for Protected State ```typescript import { TestBed } from '@angular/core/testing'; import { unprotected } from '@ngrx/signals/testing'; describe('CounterStore', () =&gt; { it('recomputes doubleCount on count changes', () =&gt; { const counterStore = TestBed.inject(CounterStore); patchState(unprotected(counterStore), { count: 10 }); expect(counterStore.doubleCount()).toBe(20); }); }); ``` ### Example: Testing Methods and Async Flows ```typescript import { TestBed, fakeAsync, tick } from '@angular/core/testing'; describe('MoviesStore', () =&gt; { it('should load movies of Warner Bros', fakeAsync(() =&gt; { const moviesService = { load: () =&gt; Promise.resolve([ { id: 1, name: 'Harry Potter' }, { id: 2, name: 'The Dark Knight' }, ]), }; TestBed.configureTestingModule({ providers: [{ provide: MoviesService, useValue: moviesService }], }); const store = TestBed.inject(MoviesStore); store.load('Warner Bros'); expect(store.loading()).toBe(true); tick(); expect(store.moviesCount()).toBe(2); expect(store.loading()).toBe(false); })); }); ``` ### Example: Mocking the Store in a Component Test ```typescript it('should show movies (native Jest)', () =&gt; { const load = jest.fn]&gt;(); const moviesStore = { movies: signal([]), loading: signal(false), load, }; TestBed.configureTestingModule({ imports: [MoviesComponent], providers: [{ provide: MoviesStore, useValue: moviesStore }], }); const fixture = TestBed.createComponent(MoviesComponent); fixture.autoDetectChanges(true); // ...assertions... }); ``` ### Example: Testing Custom Extensions ```typescript describe('withTrackedPlay', () =&gt; { const TrackedPlayStore = signalStore({ providedIn: 'root' }, withPlayTracking()); it('should track movies', fakeAsync(() =&gt; { const store = TestBed.inject(TrackedPlayStore); store.play(1); tick(1000); store.stop(); store.play(2); tick(1000); store.play(3); tick(1000); store.play(1); tick(1000); store.stop(); expect(store.trackedData()).toEqual({ 1: 2000, 2: 1000, 3: 1000 }); })); }); ``` ## 9. Migration from NgRx Store to Signal Store - **Incremental Approach:** Migrate one feature at a time - **Parallel Usage:** Use both NgRx Store and Signals Store during migration - **Facade Pattern:** Use facades to abstract store implementation details - **Component Migration:** Start with component-specific state - **Testing Coverage:** Maintain testing coverage during migration ```typescript // Facade pattern for abstraction during migration @Injectable({ providedIn: 'root' }) export class UserFacade { // Traditional NgRx Store selectors readonly users$ = this.store.select(selectAllUsers); readonly selectedUser$ = this.store.select(selectSelectedUser); // Signal Store state (for migration) private readonly signalStore = inject(UserSignalStore); private readonly store = inject(Store); // Methods that could use either implementation loadUsers(): void { // During migration, you might call both or either based on feature flags this.store.dispatch(loadUsers()); this.signalStore.loadUsers(); } selectUser(id: string): void { this.store.dispatch(selectUser({ id })); this.signalStore.selectUser(id); } } ``` ## 10. Project-Specific Patterns ### Signal Store Organization - **Store Location:** Place store definitions (`*.store.ts`) in dedicated files, often co-located with the feature module or components they serve. - **Store Naming:** Use a consistent naming convention, e.g., `FeatureNameStore`. - **Model Co-location:** Keep related state interfaces and models (`*.model.ts` or within the store file for simple cases) close to the store definition. - **Provider Functions:** Create provider functions (`provideFeatureNameStore()`) for encapsulating store providers, especially for feature stores. ```typescript // Store provider function example import { Provider } from '@angular/core'; import { UserStore } from './user.store'; export function provideUserSignalStore(): Provider { return UserStore; } // In app.config.ts or feature route configuration import { ApplicationConfig } from '@angular/core'; import { provideHttpClient } from '@angular/common/http'; export const appConfig: ApplicationConfig = { providers: [provideHttpClient(), provideUserSignalStore()], }; ``` ### Component Store Hierarchy - **Parent-Child Store Relationships:** Define clear relationships between stores - **State Sharing:** Share state between related components - **State Ownership:** Clearly define which store owns which state - **Store Composition:** Compose stores for complex UIs ### Signal Store Best Practices for Monorepo - **Library Boundaries:** Respect clear boundaries between libraries - **Shared Stores:** Define strategy for sharing stores across applications - **Store Documentation:** Document store APIs and usage patterns - **Versioning:** Handle versioning of shared stores - **Prefer Protected State:** Ensure state changes are managed only by the Signal Store by keeping the state protected. Avoid setting `{ protectedState: false }`. Explicitly set `{ protectedState: true }` or omit the option (which defaults to `true`) to prevent unintended external modifications and maintain clear ownership of state changes.

# State Management Standards for Clean Code This document outlines coding standards for state management within Clean Code principles. It provides specific guidelines and examples to ensure code related to state is maintainable, readable, performant, and secure. These standards are designed to work with the latest recommended practices and features within the Clean Code ecosystem. ## 1. Principles of Clean State Management Clean state management is about structuring your application's data in a way that's predictable, manageable, and testable. It involves making state changes explicit, limiting side effects, and ensuring data consistency. Applying clean code principles to state enhances maintainability, reduces bugs, and improves collaborative development. * **Single Source of Truth:** Ensure each piece of data has one authoritative source. This prevents inconsistencies and simplifies debugging. * **Immutability:** Favor immutable data structures. Immutable data makes state changes more predictable and helps prevent unintended side effects. * **Explicit State Transitions:** State transitions should be clear and well-defined, making it easier to understand how the application evolves over time. * **Separation of Concerns:** Keep state management logic separate from UI components or business logic. This enhances modularity and testability. * **Minimal Global State:** Limit the use of global state. Widespread global state can make it difficult to track dependencies and lead to unexpected behavior. ## 2. Architectural Patterns for State Management Choosing the right architecture for state management depends on the complexity of the application. Here are a few common patterns and guidelines: ### 2.1 Local State Managing state within a single component should be a default option. You typically use local state for isolated functionalities that don't necessitate sharing state or reactivity beyond the component’s scope. * **Do This:** Use local state for isolated component features. * **Don't Do This:** Share local state directly between unrelated components. """javascript // Example React local state using useState import React, { useState } from 'react'; function Counter() { const [count, setCount] = useState(0); return ( <div> <p>Count: {count}</p> <button onClick={() => setCount(count + 1)}>Increment</button> </div> ); } """ ### 2.2 Redux Pattern (Centralized State) The Redux pattern emphasizes a single store for application state, using reducers to handle actions and state transitions immutably. * **Do This:** * Use Redux or similar libraries for complex, application-wide state. * Define actions as plain objects with a "type" field. * Use pure functions as reducers to ensure predictable state transitions. * Selectors should cache results to prevent unnecessary re-renders. * **Don't Do This:** * Mutate the state directly in reducers. * Perform asynchronous operations directly in reducers. * Overuse Redux for simple components with minimal state. """javascript // Example Redux setup // Action const INCREMENT = 'INCREMENT'; const DECREMENT = 'DECREMENT'; const increment = () => ({ type: INCREMENT }); const decrement = () => ({ type: DECREMENT }); // Reducer const initialState = { count: 0 }; const counterReducer = (state = initialState, action) => { switch (action.type) { case INCREMENT: return { ...state, count: state.count + 1 }; case DECREMENT: return { ...state, count: state.count - 1 }; default: return state; } }; // Store creation import { createStore } from 'redux'; const store = createStore(counterReducer); // Component integration (React example) import { useSelector, useDispatch } from 'react-redux'; function CounterComponent() { const count = useSelector(state => state.count); const dispatch = useDispatch(); return ( <div> <p>Count: {count}</p> <button onClick={() => dispatch(increment())}>Increment</button> <button onClick={() => dispatch(decrement())}>Decrement</button> </div> ); } """ ### 2.3 Context API (Scoped State) Context API provides a way to pass data through the component tree without having to pass props manually at every level. While it is simpler than Redux it is still intended for scenarios that benefit from shared state. * **Do This:** * Use Context API for theming, user authentication, or other application-wide configurations. * Use "useContext" hook to consume context values. * Combine Context API with "useReducer" for complex state logic. * **Don't Do This:** * Use Context API as a general replacement for prop drilling in scenarios where component composition is better suited. * Overuse Context API resulting in unnecessary re-renders. """javascript // Example Context API setup import React, { createContext, useContext, useState } from 'react'; // Create Context const ThemeContext = createContext(); // Context Provider function ThemeProvider({ children }) { const [theme, setTheme] = useState('light'); const toggleTheme = () => { setTheme(prevTheme => (prevTheme === 'light' ? 'dark' : 'light')); }; return ( <ThemeContext.Provider value={{ theme, toggleTheme }}> {children} </ThemeContext.Provider> ); } // Custom Hook to consume Context function useTheme() { return useContext(ThemeContext); } // Component using Context function ThemeToggler() { const { theme, toggleTheme } = useTheme(); return ( <button onClick={toggleTheme}> Toggle Theme (Current: {theme}) </button> ); } // Usage in App function App() { return ( <ThemeProvider> <div> <ThemeToggler /> </div> </ThemeProvider> ); } """ ### 2.4 Observable Pattern (Reactive State) The observable pattern, often implemented with libraries like RxJS, is used for handling asynchronous data streams and complex event-driven applications. * **Do This:** * Use RxJS or similar libraries for handling asynchronous data streams. * Structure application logic as a pipeline of observable transformations. * Use subjects to bridge different parts of the application. * **Don't Do This:** * Overuse RxJS for simple event handling. * Introduce memory leaks by not unsubscribing from observables. * Create overly complex observable chains that are hard to understand. """javascript // Example RxJS setup import { fromEvent, interval } from 'rxjs'; import { map, filter, scan, takeUntil } from 'rxjs/operators'; // Example: Click counter observable const button = document.getElementById('myButton'); const click$ = fromEvent(button, 'click'); const counter$ = click$.pipe( map(() => 1), scan((acc, value) => acc + value, 0) ); counter$.subscribe(count => { console.log("Button clicked ${count} times"); }); // Example: Auto-incrementing counter that stops after 5 seconds const interval$ = interval(1000); const stop$ = fromEvent(document.getElementById('stopButton'), 'click'); interval$.pipe( takeUntil(stop$) // Stop the interval when the stop button is clicked ).subscribe(val => console.log("Interval value: ${val}")); """ ### 2.5 State Machines State machines are useful for managing complex state transitions with clearly defined states and transitions. * **Do This:** * Use state machines for scenarios with clearly defined states and transitions. * Model state transitions explicitly, reducing possible unexpected states. * Ensure state machines are well-documented, especially for complex systems. * **Don't Do This:** * Overuse state machines for simple state management. * Create monolithic state machines that are difficult to understand. """javascript // Example: JavaScript state machine using XState import { createMachine, interpret } from 'xstate'; // Define the state machine const trafficLightMachine = createMachine({ id: 'trafficLight', initial: 'green', states: { green: { after: { 5000: 'yellow' // After 5 seconds, transition to yellow } }, yellow: { after: { 1000: 'red' // After 1 second, transition to red } }, red: { after: { 6000: 'green' // After 6 seconds, transition to green } } } }); // Interpret the state machine const trafficService = interpret(trafficLightMachine).start(); trafficService.onTransition(state => { console.log("Traffic light is now ${state.value}"); }); // Example usage (simulating events or external triggers) // trafficService.send('TIMER'); """ ## 3. Implementing Immutability Immutability ensures that once an object is created, its state cannot be changed. This helps prevent accidental state mutations, making it easier to track and manage state changes, which aids in debugging and improves performance in certain scenarios. * **Do This:** * Use immutable data structures and operations. * Make copies of objects or arrays before modifying them. * Employ libraries like Immutable.js for more complex scenarios. * **Don't Do This:** * Directly modify object properties or array elements. * Assume that passing an object or array creates a new copy. ### 3.1 JavaScript Immutability Techniques """javascript // Immutable Object Update const originalObject = { name: 'John', age: 30 }; const updatedObject = { ...originalObject, age: 31 }; // Create a new object // Immutable Array Update const originalArray = [1, 2, 3]; const updatedArray = [...originalArray, 4]; // Create a new array const removedArray = originalArray.filter(item => item !== 2); // Create new array without '2' console.log(originalObject); // { name: 'John', age: 30 } console.log(updatedObject); // { name: 'John', age: 31 } console.log(originalArray); // [1, 2, 3] console.log(updatedArray); // [1, 2, 3, 4] console.log(removedArray); // [1, 3] """ ### 3.2 Immutable.js Immutable.js provides persistent immutable data structures, improving performance and simplifying state management for complex applications. """javascript import { Map, List } from 'immutable'; // Immutable Map const originalMap = Map({ name: 'John', age: 30 }); const updatedMap = originalMap.set('age', 31); // Immutable List const originalList = List([1, 2, 3]); const updatedList = originalList.push(4); console.log(originalMap.toJS()); // { name: 'John', age: 30 } console.log(updatedMap.toJS()); // { name: 'John', age: 31 } console.log(originalList.toJS()); // [1, 2, 3] console.log(updatedList.toJS()); // [1, 2, 3, 4] """ ## 4. Handling Side Effects Side effects are operations that affect the state of the application outside of the current function or component. Properly managing side effects is crucial for maintaining predictable and testable code. * **Do This:** * Isolate side effects in dedicated functions or modules. * Use effect hooks (e.g., "useEffect" in React) to manage side effects in components. * Handle errors gracefully when performing side effects. * **Don't Do This:** * Perform side effects directly within reducers or pure functions. * Ignore potential errors in side effect operations. ### 4.1 Managing Effects with "useEffect" """javascript import React, { useState, useEffect } from 'react'; function DataFetcher({ url }) { const [data, setData] = useState(null); const [loading, setLoading] = useState(true); const [error, setError] = useState(null); useEffect(() => { const fetchData = async () => { try { const response = await fetch(url); if (!response.ok) { throw new Error("HTTP error! status: ${response.status}"); } const result = await response.json(); setData(result); } catch (e) { setError(e); } finally { setLoading(false); } }; fetchData(); // Cleanup function (optional) return () => { // Cancel any pending requests or subscriptions }; }, [url]); // Dependency array: effect runs only when 'url' changes if (loading) return <p>Loading...</p>; if (error) return <p>Error: {error.message}</p>; if (!data) return <p>No data available.</p>; return ( <pre>{JSON.stringify(data, null, 2)}</pre> ); } """ ### 4.2 Using Thunks with Redux Thunks allow you to perform asynchronous operations in Redux actions. """javascript // Example Redux Thunk Action const fetchDataRequest = () => ({ type: 'FETCH_DATA_REQUEST' }); const fetchDataSuccess = (data) => ({ type: 'FETCH_DATA_SUCCESS', payload: data }); const fetchDataFailure = (error) => ({ type: 'FETCH_DATA_FAILURE', payload: error }); // Async action using Redux Thunk const fetchData = (url) => { return async (dispatch) => { dispatch(fetchDataRequest()); try { const response = await fetch(url); if (!response.ok) { throw new Error("HTTP error! status: ${response.status}"); } const data = await response.json(); dispatch(fetchDataSuccess(data)); } catch (error) { dispatch(fetchDataFailure(error.message)); } }; }; // Usage in Component import { useDispatch } from 'react-redux'; function DataFetchButton({ url }) { const dispatch = useDispatch(); return ( <button onClick={() => dispatch(fetchData(url))}> Fetch Data </button> ); } """ ## 5. Testing State Management Testing state management involves verifying that state transitions occur correctly and that side effects are handled properly. * **Do This:** * Write unit tests for reducers to verify state transitions. * Use mock stores and actions to test components connected to Redux. * Test side effects by mocking external dependencies. * **Don't Do This:** * Omit testing for state management logic. * Write integration tests without proper unit testing. ### 5.1 Testing Reducers """javascript // Reducer Test Example (Jest) import counterReducer from './counterReducer'; // Assuming counterReducer.js import { INCREMENT, DECREMENT } from './actions'; describe('counterReducer', () => { it('should return the initial state', () => { expect(counterReducer(undefined, {})).toEqual({ count: 0 }); }); it('should handle INCREMENT', () => { expect(counterReducer({ count: 0 }, { type: INCREMENT })).toEqual({ count: 1 }); }); it('should handle DECREMENT', () => { expect(counterReducer({ count: 1 }, { type: DECREMENT })).toEqual({ count: 0 }); }); }); """ ### 5.2 Testing React Components with Redux """javascript // Component Test Example (React Testing Library and Redux Mock Store) import React from 'react'; import { render, fireEvent } from '@testing-library/react'; import { Provider } from 'react-redux'; import configureStore from 'redux-mock-store'; import CounterComponent from './CounterComponent'; // Assuming CounterComponent.js const mockStore = configureStore([]); describe('CounterComponent', () => { let store; let component; beforeEach(() => { store = mockStore({ count: 0 }); store.dispatch = jest.fn(); // Mock dispatch function component = render( <Provider store={store}> <CounterComponent /> </Provider> ); }); it('should display the initial count', () => { expect(component.getByText('Count: 0')).toBeInTheDocument(); }); it('should dispatch increment action when increment button is clicked', () => { fireEvent.click(component.getByText('Increment')); expect(store.dispatch).toHaveBeenCalledWith({ type: 'INCREMENT' }); }); }); """ ## 6. Security Considerations for State Management Security is a critical aspect of state management. Properly securing the state ensures that sensitive data is protected from unauthorized access and tampering. * **Do This:** * Protect sensitive data in the state with encryption. * Validate data received from external sources before storing it in the state. * Sanitize user input to prevent XSS. * **Don't Do This:** * Store sensitive data in plain text in the state. * Trust data received from external sources without validation. * Expose sensitive data in logs or error messages. ### 6.1 Data Validation """javascript // Example Data Validation const validateData = (data) => { if (typeof data.email !== 'string' || !data.email.includes('@')) { throw new Error('Invalid email format'); } if (typeof data.age !== 'number' || data.age < 0 || data.age > 120) { throw new Error('Invalid age'); } return data; }; // Usage in Reducer const userReducer = (state = {}, action) => { switch (action.type) { case 'UPDATE_USER': try { const validatedData = validateData(action.payload); return { ...state, ...validatedData }; } catch (error) { console.error('Data validation failed:', error.message); return state; } default: return state; } }; """ ### 6.2 Encryption Encrypting sensitive data ensures that even if the state is compromised, the data remains unreadable without the decryption key. """javascript // Example Encryption (using CryptoJS) import CryptoJS from 'crypto-js'; const encryptData = (data, key) => { const encrypted = CryptoJS.AES.encrypt(JSON.stringify(data), key).toString(); return encrypted; }; const decryptData = (encryptedData, key) => { const bytes = CryptoJS.AES.decrypt(encryptedData, key); try { const decrypted = JSON.parse(bytes.toString(CryptoJS.enc.Utf8)); return decrypted; } catch (e) { console.error("Decryption error", e); return null; // Or handle the error as appropriate } }; // Example usage const sensitiveData = { creditCardNumber: '1234-5678-9012-3456' }; const encryptionKey = 'my-secret-key'; const encryptedData = encryptData(sensitiveData, encryptionKey); console.log('Encrypted:', encryptedData); const decryptedData = decryptData(encryptedData, encryptionKey); console.log('Decrypted:', decryptedData); """ ## 7. Optimizing Performance Efficient state management is crucial for optimizing application performance, especially in complex applications with frequent state updates. * **Do This:** * Use memoization techniques to prevent unnecessary re-renders. * Implement lazy loading for components that rely on large state objects. * Batch state updates to minimize the number of renders. * **Don't Do This:** * Update the state unnecessarily. * Cause components to re-render frequently with negligible impact. ### 7.1 Memoization Memoization prevents re-renders by caching the results of expensive calculations or component renders. """javascript import React, { useState, useMemo } from 'react'; function ExpensiveComponent({ data }) { // Simulate an expensive computation const computedValue = useMemo(() => { console.log('Computing expensive value...'); // Complex calculation based on data return data.map(item => item * 2).reduce((acc, val) => acc + val, 0); }, [data]); // Only recompute if 'data' changes return ( <div> <p>Computed Value: {computedValue}</p> </div> ); } function ParentComponent() { const [count, setCount] = useState(0); const data = [1, 2, 3, 4, 5]; // Static data return ( <div> <button onClick={() => setCount(count + 1)}>Increment Count</button> <p>Count: {count}</p> {/*ExpensiveComponent only re-renders if "data" changes, not on count changes*/} <ExpensiveComponent data={data} /> </div> ); } function MemoizedComponent({ data }) { // Simulate a render-heavy component console.log('Rendering MemoizedComponent...'); return <p>Data: {data.join(', ')}</p>; } // Memoize MemoizedComponent to prevent unnecessary re-renders const OptimizedMemoizedComponent = React.memo(MemoizedComponent); function ParentMemoComponent() { const [count, setCount] = useState(0); const data = [1, 2, 3, 4, 5]; return ( <div> <button onClick={() => setCount(count + 1)}>Increment Count</button> <p>Count: {count}</p> {/* MemoizedComponent only re-renders if its props change, not on count changes */} <OptimizedMemoizedComponent data={data} /> </div> ); } """ ### 7.2 Batching Updates Batching updates ensures that multiple state updates are grouped into a single render cycle. """javascript import React, { useState } from 'react'; import { unstable_batchedUpdates } from 'react-dom'; // Available only in some React versions function BatchUpdatesComponent() { const [count1, setCount1] = useState(0); const [count2, setCount2] = useState(0); const updateBothCounts = () => { unstable_batchedUpdates(() => { // Both state updates are batched into a single render setCount1(prevCount => prevCount + 1); setCount2(prevCount => prevCount + 1); }); }; return ( <div> <p>Count 1: {count1}</p> <p>Count 2: {count2}</p> <button onClick={updateBothCounts}>Update Both Counts</button> </div> ); } """ These standards provide a comprehensive guide to managing state in a clean and maintainable way. By following these guidelines, developers can build robust, performant, and secure applications.

# API Integration Standards for Clean Code This document outlines coding standards and best practices for integrating with backend services and external APIs within the Clean Code framework. It emphasizes readability, maintainability, performance, and security. These standards are aimed at guiding developers and AI coding assistants in producing high-quality, robust, and scalable integrations. ## 1. API Integration Principles and Clean Code API integration, when approached with Clean Code principles in mind, becomes significantly more manageable and less prone to errors. This section explores the core principles and their applications in the context of API interactions. * **Single Responsibility Principle (SRP):** A class or module should have one, and only one, reason to change. For API integration, this means separating the API client logic (responsible for making requests and handling responses) from the business logic that uses the data. * **Do This:** Create dedicated classes or modules for interacting with specific APIs, encapsulating all the API-related logic within them. * **Don't Do This:** Mix API calls directly within business logic classes or functions. This makes testing and maintenance difficult. * **Why:** SRP ensures that a change in the API (e.g., endpoint change, data format update) only requires modification in the API client module, not the entire application. * **Open/Closed Principle (OCP):** Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification. This principle applies to API integration by allowing new API features or versions to be adopted without modifying existing code that uses the API. * **Do This:** Use abstract classes or interfaces to define a contract for API clients. Implementations can then be created for different API versions or services. Utilize design patterns such as Strategy or Template Method. * **Don't Do This:** Directly modify existing API client code to accommodate new API features. * **Why:** OCP ensures that changes to the API don't introduce regressions in existing functionality. * **Liskov Substitution Principle (LSP):** Subtypes must be substitutable for their base types without altering the correctness of the program. This is relevant when using polymorphism with API clients. * **Do This:** Ensure that any derived API client classes adhere to the contract defined by the base class or interface. If a method implemented in a sub-class modifies behavior in an unexpected way, it violates LSP. * **Don't Do This:** Create API client subclasses that fundamentally change the behavior of the base class's methods. * **Why:** LSP ensures that you can replace one API client implementation with another without causing unexpected errors. * **Interface Segregation Principle (ISP):** Clients should not be forced to depend on methods they do not use. In the API realm, this translates to creating specific interfaces for different API functionalities, catering to the needs of different parts of the application. * **Do This:** Define multiple, smaller interfaces tailored to specific use cases, rather than a single large interface for the entire API. * **Don't Do This:** Force clients to implement methods they don't need, leading to bloated and confusing implementations. * **Why:** ISP promotes loose coupling and reduces the risk of unintended side effects when API contracts change. * **Dependency Inversion Principle (DIP):** High-level modules should not depend on low-level modules. Both should depend on abstractions. Abstractions should not depend on details. Details should depend on abstractions. In API integration, this means that business logic should depend on interfaces for API clients, not on concrete implementations. That allows easy swapping of implementations for testing, changing providers, or other needs. * **Do This:** Inject API client interfaces into classes that need to consume the API. * **Don't Do This:** Directly instantiate API client classes within business logic components. * **Why:** DIP promotes loose coupling, making testing easier, and allowing you to switch API providers without impacting the rest of your system. Dependency Injection (DI) frameworks are invaluable here. ## 2. Connecting with Backend Services and External APIs This section covers the practical aspects of connecting to APIs, including error handling, data transformation, and authentication. ### 2.1 Selecting an HTTP Client * **Standard:** Use a robust and well-maintained HTTP client library. Consider "aiohttp" (async) or "requests" (sync) for Python. For Javascript consider "axios" or the native "fetch" API. * **Do This:** Choose a library that supports features like connection pooling, automatic retries, timeouts, and request/response interceptors, and proper TLS/SSL verification. * **Don't Do This:** Write your own HTTP client or use a rudimentary library that lacks essential features. * **Why:** Using a mature HTTP client library simplifies development and reduces the risk of introducing bugs or security vulnerabilities. """python import requests def get_data_from_api(url): try: response = requests.get(url, timeout=10) # added timeout response.raise_for_status() # Raise HTTPError for bad responses (4xx or 5xx) return response.json() except requests.exceptions.RequestException as e: print(f"Error communicating with API: {e}") return None api_url = "https://example.com/api/data" data = get_data_from_api(api_url) if data: print(data) """ ### 2.2 Error Handling * **Standard:** Implement robust error handling to gracefully handle API failures. Use "try-except" blocks, check response codes, and log errors appropriately. Implement retry mechanisms with exponential backoff for transient errors. * **Do This:** Wrap API calls in "try-except" blocks to catch potential exceptions (e.g., network errors, timeouts, invalid responses). Use "response.raise_for_status()" to check for HTTP errors, making special consideration for rate limiting. Log the complete error message, request URL, and any relevant context. * **Don't Do This:** Ignore errors or simply print error messages without proper logging and handling. * **Why:** Proper error handling prevents application crashes, provides valuable debugging information, and ensures a better user experience. """python import requests import time import logging logging.basicConfig(level=logging.INFO) def get_data_from_api(url, max_retries=3, backoff_factor=2): # retry mechanism retries = 0 while retries < max_retries: try: response = requests.get(url, timeout=10) response.raise_for_status() return response.json() except requests.exceptions.RequestException as e: logging.error(f"Attempt {retries + 1} failed: {e}") retries += 1 time.sleep(backoff_factor ** retries) # Exponential backoff logging.error(f"Failed to retrieve data from {url} after {max_retries} attempts") return None """ ### 2.3 Data Transformation * **Standard:** Decouple the API's data format from your application's data model. Use data transfer objects (DTOs) or similar mechanisms to map the API response to your internal representation. * **Do This:** Create dedicated classes or functions to transform API responses into your application's data structures. Centralize this mapping logic to simplify changes. Use validation libraries like Pydantic (for Python) for structural validation and automated type conversion. * **Don't Do This:** Directly use the API's data format throughout your application. This tightly couples your code to the API and makes it difficult to adapt to changes. * **Why:** Data transformation ensures that your application remains independent of the specific API's data format, improving maintainability and flexibility. """python from pydantic import BaseModel import requests class User(BaseModel): # pydantic model id: int name: str email: str def get_user_from_api(user_id: int) -> User | None: url = f"https://example.com/api/users/{user_id}" try: response = requests.get(url) response.raise_for_status() user_data = response.json() return User(**user_data) # Validate and convert using Pydantic except requests.exceptions.RequestException as e: print(f"Error: {e}") return None user = get_user_from_api(1) if user: print(f"User name: {user.name}") """ ### 2.4 Authentication and Authorization * **Standard:** Implement secure authentication and authorization mechanisms according to the API's requirements (API Keys, OAuth 2.0, JWT). Store secrets securely using environment variables or dedicated secret management tools. * **Do This:** Use a dedicated library for handling authentication protocols. Store API keys and secrets securely (e.g., using environment variables or a vault). Properly handle token refresh flows in OAuth 2.0 when using access tokens with limited lifetimes. Use HTTPS for all API communication. * **Don't Do This:** Hardcode API keys or secrets in your code. Skip SSL/TLS verification. Store cryptographic keys anywhere in your source repository. * **Why:** Secure authentication and authorization protect your application and the API from unauthorized access. """python import os import requests API_KEY = os.environ.get("MY_API_KEY") # Store in environment variable def call_api_with_auth(url): headers = {"Authorization": f"Bearer {API_KEY}"} # authorization header response = requests.get(url, headers=headers) response.raise_for_status() return response.json() """ ### 2.5 Rate Limiting * **Standard:** Understand and respect the API's rate limits. Implement mechanisms to avoid exceeding these limits, such as caching, throttling, and exponential backoff with jitter. * **Do This:** Check the API's documentation for rate limits. Implement a throttling mechanism to control the number of requests per unit of time. Cache API responses when appropriate (especially for frequently accessed data that doesn't change often). Handle "429 Too Many Requests" errors gracefully using exponential backoff and jitter. * **Don't Do This:** Ignore rate limits and bombard the API with requests. This can lead to temporary or permanent blocking. * **Why:** Respecting rate limits ensures fair usage of the API and prevents your application from being blocked. """python import time import requests import logging import random logging.basicConfig(level=logging.INFO) def call_api_with_rate_limiting(url, delay=1): try: response = requests.get(url) response.raise_for_status() return response.json() except requests.exceptions.HTTPError as e: if e.response.status_code == 429: retry_after = int(e.response.headers.get("Retry-After", 60)) # get from header jitter = random.uniform(0, 1) # add jitter wait_time = retry_after + jitter logging.warning(f"Rate limit exceeded. Waiting {wait_time:.2f} seconds.") time.sleep(wait_time) return call_api_with_rate_limiting(url) # Recursive call! else: raise # Re-raise the exception for other errors time.sleep(delay) # delay for a specified time return response.json() """ ## 3. Design Patterns for API Integration Several design patterns can help improve the structure and maintainability of API integration code. ### 3.1 Facade Pattern * **Standard:** Use a facade to provide a simplified interface to a complex API. This hides the underlying complexity and makes it easier for clients to use the API. * **Do This:** Create a facade class that encapsulates the API client and provides a simple, high-level interface for common operations. * **Don't Do This:** Expose the raw API client directly to clients. This exposes unnecessary complexity and makes it harder to adapt to API changes. * **Why:** The Facade pattern shields calling code from the complexities of direct API interaction. """python import requests class WeatherAPIClient: BASE_URL = "https://api.weatherapi.com/v1" def __init__(self, api_key): self.api_key = api_key def get_current_weather(self, city): url = f"{self.BASE_URL}/current.json?key={self.api_key}&q={city}" response = requests.get(url) response.raise_for_status() return response.json() class WeatherFacade: def __init__(self, api_key): self.api_client = WeatherAPIClient(api_key) # encapsulates API def get_temperature(self, city): data = self.api_client.get_current_weather(city) return data["current"]["temp_c"] # simplified interface # Usage: weather_facade = WeatherFacade("YOUR_API_KEY") temperature = weather_facade.get_temperature("London") print(f"Temperature in London: {temperature}°C") """ ### 3.2 Adapter Pattern * **Standard:** Use an adapter to convert the interface of an API client class into another interface that clients expect. This is useful when integrating with APIs that have different interfaces. * **Do This:** Create an adapter class that implements the desired interface and delegates calls to the API client. Use this pattern to normalize interfaces from different API endpoint calls to make them consistent for calling code. * **Don't Do This:** Modify the API client class directly to fit the desired interface (violates OCP). * **Why:** The Adapter pattern allows integrating disparate API interfaces or data models into a common format. """python class OldAPI: def fetch_data(self): return {"old_data": "value"} class NewAPIInterface: def get_data(self): raise NotImplementedError class OldAPIToNewAPIAdapter(NewAPIInterface): # Adapter class def __init__(self, old_api): self.old_api = old_api def get_data(self): old_data = self.old_api.fetch_data() return {"new_data": old_data["old_data"]} old_api = OldAPI() adapter = OldAPIToNewAPIAdapter(old_api) new_data = adapter.get_data() print(new_data) # Output: {'new_data': 'value'} """ ### 3.3 Strategy Pattern * **Standard:** If you have multiple ways to call an API (different authentication methods, different endpoints for the same functionality, etc.) use the Strategy pattern to encapsulate each approach into a separate strategy class. This allows you to easily switch between strategies at runtime. * **Do This:** Define a common interface for all strategies. Create concrete strategy classes for each approach. Inject the desired strategy into the class that needs to call the API. * **Don't Do This:** Use conditional statements to switch between different approaches. This makes the code harder to read and maintain. * **Why:** Provides implementation flexibility and facilitates switching strategies without modifying the core logic. """python import requests class AuthStrategy: def apply_auth(self, request): raise NotImplementedError() class APIKeyAuth(AuthStrategy): def __init__(self, api_key): self.api_key = api_key def apply_auth(self, request): request.headers["X-API-Key"] = self.api_key return request class OAuth2Auth(AuthStrategy): def __init__(self, token): self.token = token def apply_auth(self, request): request.headers["Authorization"] = f"Bearer {self.token}" return request class APIClient: def __init__(self, auth_strategy: AuthStrategy): self.auth_strategy = auth_strategy def get(self, url): request = requests.Request("GET", url) prepared_request = self.auth_strategy.apply_auth(request) # apply strategy session = requests.Session() response = session.send(prepared_request.prepare()) response.raise_for_status() return response.json() # Usage: api_key_auth = APIKeyAuth("your_api_key") api_client_api_key = APIClient(api_key_auth) data = api_client_api_key.get("https://example.com/api/data") print(data) oauth2_auth = OAuth2Auth("your_oauth_token") api_client_oauth = APIClient(oauth2_auth) data = api_client_oauth.get("https://example.com/api/data") print(data) """ ## 4. Technology-Specific Considerations ### 4.1 Python * **Asyncio:** Utilize "asyncio" and "aiohttp" for asynchronous API calls to improve concurrency and performance in I/O-bound applications. * **Type Hints:** Use type hints extensively to improve code readability and catch type-related errors early. * **Pydantic:** Use Pydantic for data validation and serialization/deserialization of API requests and responses. * **Requests Library:** Using "requests" may block synchronous code so consider using threading to avoid impacting performance or using Asyncio libraries. ### 4.2 JavaScript * **Fetch API/Axios:** Use "fetch" (native) or "axios" (library) for making HTTP requests. Axios is typically preferred for providing additional error handling and legacy browser support. * **Async/Await:** Leverage "async/await" syntax for asynchronous API calls to improve code readability and maintainability. * **Typescript:** Enable TypeScript support to statically type check code during development, ensuring that API requests are correctly constructed, and API responses are properly handled. * **Node.js:** Utilize Node.js to process large amounts of asynchronous requests. ## 5. Testing API Integrations * **Standard:** Thoroughly test API integrations to ensure correctness, reliability, and performance. Use mock APIs or stubs to isolate your code during testing. * **Do This:** Write unit tests for API client classes, mocking the HTTP client to control the API responses. Use integration tests to verify the end-to-end flow, including actual API calls to a test environment. Consider contract testing to ensure that your API client adheres to the API's contract. * **Don't Do This:** Skip testing API integrations or rely solely on manual testing. This can lead to unexpected errors and regressions. * **Why:** Testing API integrations ensures that your application works correctly with the API and protects against changes in the API. """python import unittest from unittest.mock import patch import requests class MockResponse: def __init__(self, json_data, status_code): self.json_data = json_data self.status_code = status_code def json(self): return self.json_data def raise_for_status(self): if self.status_code >= 400: raise requests.exceptions.HTTPError("Error") class APITest(unittest.TestCase): @patch('requests.get') # Mock the requests.get method def test_get_data_from_api_success(self, mock_get): mock_response = MockResponse({"key": "value"}, 200) mock_get.return_value = mock_response from your_module import get_data_from_api # Import your function here data = get_data_from_api("http://example.com/api") self.assertEqual(data, {"key": "value"}) @patch('requests.get') def test_get_data_from_api_failure(self, mock_get): mock_response = MockResponse(None, 500) mock_response.raise_for_status = unittest.mock.Mock(side_effect=requests.exceptions.HTTPError("Error")) mock_get.return_value = mock_response from your_module import get_data_from_api data = get_data_from_api("http://example.com/api") self.assertIsNone(data) """ ## 6. Documentation * **Standard:** Document all API integrations, including the API's purpose, authentication methods, request/response formats, and error handling strategies. * **Do This:** Use docstrings to document API client classes and methods. Create separate documents or wikis to describe the API integration in more detail. Use tooling like Swagger or OpenAPI to document APIs and their integration points. * **Don't Do This:** Leave API integrations undocumented. This makes it difficult for others (and yourself in the future) to understand and maintain the code. * **Why:** Clear documentation is essential for maintainability and collaboration. ## 7. Security Considerations * **Standard:** Prioritize security when integrating with APIs. Enforce HTTPS, validate input, sanitize output, and protect against common web vulnerabilities. * **Do This:** Always use HTTPS for API communication. Validate all input data to prevent injection attacks. Sanitize all output data to prevent cross-site scripting (XSS) attacks. Follow the principle of least privilege when configuring API access controls. Protect against CSRF attacks. * **Don't Do This:** Store sensitive data in plain text. Trust user input without validation. Disable security features. * **Why:** Security vulnerabilities can expose sensitive data and compromise your application. By adhering to these standards, developers can ensure that API integrations are clean, maintainable, performant, and secure, aligning with the core principles of Clean Code.