# Architecture Document
Generated: Tuesday, September 16, 2025

## System Overview
The Angular Clarity Boilerplate is a frontend-only, single-page application (SPA) template. It is designed to serve as a foundational starting point for developing enterprise-grade web applications. The system provides a pre-configured, modular, and scalable architecture using the Angular framework and is visually styled with the VMware Clarity Design System. Its primary purpose is to accelerate development by providing a structured and feature-rich starting point.

## Architecture Pattern
The boilerplate is built upon a **Component-Based Architecture**, which is fundamental to the Angular framework. The UI is composed of a tree of reusable and encapsulated components.

The overall architectural pattern follows best practices for scalable Angular applications, emphasizing a **Modular Design**. The application is segregated into a `CoreModule`, a `SharedModule`, and is designed for the addition of multiple `FeatureModules`. This structure promotes separation of concerns, reusability, and maintainability.

## Component Design (Frontend)

- **AppModule:** The root module of the application, responsible for bootstrapping the `AppComponent` and importing essential modules like the `CoreModule` and `AppRoutingModule`.

- **AppComponent:** The main application shell component. It contains the primary layout, including the Clarity header, sidebar navigation, and the main content area where routed components are displayed via `<router-outlet>`.

- **CoreModule:** This module is designed to be imported only once by the `AppModule`. It contains singleton services, route guards, and other one-time setup logic (e.g., HTTP interceptors). This pattern prevents services from being provided multiple times across the application.

- **SharedModule:** This module contains commonly used components, directives, and pipes that can be reused across different feature modules. It is imported by feature modules whenever they need access to these shared elements. It primarily exports common Angular modules (like `CommonModule`, `FormsModule`) and Clarity UI modules.

- **Feature Modules (Conceptual):** The architecture is designed for developers to create new feature modules (e.g., `DashboardModule`, `AdminModule`). These modules encapsulate all the components, services, and routing related to a specific business domain. They are typically **lazy-loaded** to improve initial application load performance.

## Data Architecture

### Primary Database
- Not applicable. As a frontend-only boilerplate, this project does not include a database. It is designed to connect to any backend with a data persistence layer.

### Data Model (Client-Side)
- Data models will be defined using **TypeScript interfaces or classes** within feature modules. These models will represent the structure of data objects retrieved from or sent to the backend API.
- **Example `User` model:**
  ```typescript
  export interface User {
    id: number;
    name: string;
    email: string;
    role: 'admin' | 'user';
  }

  Of course. Here is the architecture_document.md for the Angular Clarity boilerplate project, presented in a single code block for easy copying.

Markdown

# Architecture Document
Generated: Tuesday, September 16, 2025

## System Overview
The Angular Clarity Boilerplate is a frontend-only, single-page application (SPA) template. It is designed to serve as a foundational starting point for developing enterprise-grade web applications. The system provides a pre-configured, modular, and scalable architecture using the Angular framework and is visually styled with the VMware Clarity Design System. Its primary purpose is to accelerate development by providing a structured and feature-rich starting point.

## Architecture Pattern
The boilerplate is built upon a **Component-Based Architecture**, which is fundamental to the Angular framework. The UI is composed of a tree of reusable and encapsulated components.

The overall architectural pattern follows best practices for scalable Angular applications, emphasizing a **Modular Design**. The application is segregated into a `CoreModule`, a `SharedModule`, and is designed for the addition of multiple `FeatureModules`. This structure promotes separation of concerns, reusability, and maintainability.

## Component Design (Frontend)

- **AppModule:** The root module of the application, responsible for bootstrapping the `AppComponent` and importing essential modules like the `CoreModule` and `AppRoutingModule`.

- **AppComponent:** The main application shell component. It contains the primary layout, including the Clarity header, sidebar navigation, and the main content area where routed components are displayed via `<router-outlet>`.

- **CoreModule:** This module is designed to be imported only once by the `AppModule`. It contains singleton services, route guards, and other one-time setup logic (e.g., HTTP interceptors). This pattern prevents services from being provided multiple times across the application.

- **SharedModule:** This module contains commonly used components, directives, and pipes that can be reused across different feature modules. It is imported by feature modules whenever they need access to these shared elements. It primarily exports common Angular modules (like `CommonModule`, `FormsModule`) and Clarity UI modules.

- **Feature Modules (Conceptual):** The architecture is designed for developers to create new feature modules (e.g., `DashboardModule`, `AdminModule`). These modules encapsulate all the components, services, and routing related to a specific business domain. They are typically **lazy-loaded** to improve initial application load performance.

## Data Architecture

### Primary Database
- Not applicable. As a frontend-only boilerplate, this project does not include a database. It is designed to connect to any backend with a data persistence layer.

### Data Model (Client-Side)
- Data models will be defined using **TypeScript interfaces or classes** within feature modules. These models will represent the structure of data objects retrieved from or sent to the backend API.
- **Example `User` model:**
  ```typescript
  export interface User {
    id: number;
    name: string;
    email: string;
    role: 'admin' | 'user';
  }
Data Flow
API Call: A component's method calls a function in its corresponding service (e.g., userService.getUsers()).

Service Layer: The service uses Angular's HttpClient to make an HTTP request to the backend API.

Data Retrieval: The service receives the HTTP response and typically returns an Observable of the data, typed with the appropriate TypeScript interface.

Component Update: The component subscribes to the Observable. Once the data is received, it updates its local state, triggering Angular's change detection to re-render the template and display the new data.

API Design (Backend Communication)
This boilerplate is backend-agnostic. It is designed to communicate with any backend that exposes a RESTful or GraphQL API.

Communication Protocol
HTTP/HTTPS: Communication is handled via standard HTTP requests using Angular's HttpClient service.

Example Service Implementation
An example of a service making API calls:
// in user.service.ts
import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';
import { User } from '../models/user.model';
import { environment } from '../../environments/environment';

@Injectable({
  providedIn: 'root'
})
export class UserService {
  private apiUrl = `${environment.apiBaseUrl}/users`;

  constructor(private http: HttpClient) { }

  getUsers(): Observable<User[]> {
    return this.http.get<User[]>(this.apiUrl);
  }

  getUserById(id: number): Observable<User> {
    return this.http.get<User>(`${this.apiUrl}/${id}`);
  }
}

Error Handling
HTTP interceptors can be provided in the CoreModule to handle API errors globally (e.g., logging errors, redirecting on 401 Unauthorized responses).

Security Architecture
Authentication: Authentication logic (e.g., handling JWTs, interacting with OAuth providers) should be encapsulated within an AuthService provided in the CoreModule.

Authorization (Route Guards): The architecture uses Angular's Route Guards to protect routes. An AuthGuard can be implemented to prevent unauthorized users from accessing certain parts of the application.

Client-Side Security: The boilerplate does not inherently protect against all client-side vulnerabilities. Developers should follow best practices for preventing XSS and CSRF attacks.

Scalability Considerations
Lazy Loading: The architecture strongly encourages the use of lazy-loaded feature modules. This ensures that the initial application bundle size remains small, leading to faster load times. As new features are added, they do not impact the initial load performance.

Modular Design: The strict separation of concerns into Core, Shared, and Feature modules makes the codebase easier to manage, test, and scale as the application grows in complexity.

State Management: For applications with complex state, a state management library like NgRx or Akita can be easily integrated into this architecture without requiring significant refactoring.

---

## ARCHITECTURE UPDATE - 2025-10-02 06:15:10


## Security Architecture Further Refinements - 2025-10-02 06:14:03

Based on the enhanced security requirements (NFR-002 from `requirements_document.md` updated at `06:12:28`), the following explicit details are added:

-   **Password Policy:** User passwords shall adhere to a minimum complexity requirement, specifically: at least 8 characters in length, including a combination of uppercase letters, lowercase letters, numbers, and special characters. This policy will be enforced during user registration and password change operations on the backend.

## Scalability Considerations Further Refinements - 2025-10-02 06:14:03

Building upon NFR-006 (Enhanced) from `requirements_document.md` (updated at `06:12:28`), the architecture aims to support:

-   **Performance Target:** The system is designed to maintain acceptable performance (e.g., note listing within 2 seconds, note save within 1 second, search within 3 seconds) for a scale of up to 100,000 notes per user and up to 10,000 concurrent users. Achieved through stateless backend, optimized database indexing, and potential caching as outlined previously.



---

## ARCHITECTURE UPDATE - 2025-10-02 06:15:22


# Architecture Document
Generated: 2025-10-02T[CURRENT_TIMESTAMP]

## System Overview
The "Notes App" is a full-stack web application designed for personal note management. It enables users to securely register, log in, and perform CRUD (Create, Read, Update, Delete) operations on their notes. Phase 2 enhancements include advanced features such as search, filtering, rich text editing, and tagging for improved organization. The frontend is built with Angular, leveraging the Clarity Design System from the base project for a consistent and intuitive user interface. The backend will expose a RESTful API to manage user authentication, notes, and associated metadata, ensuring data persistence and security.

## Architecture Pattern
### Client-Server Architecture
The application will follow a classic client-server architecture, where the Angular frontend acts as the client consuming services provided by a dedicated backend API.

### Layered Backend Architecture
The backend will implement a layered architecture to ensure separation of concerns, maintainability, and scalability:
1.  **Presentation Layer (API/Controllers):** Handles HTTP requests, authentication, request parsing, and response formatting. Exposes RESTful endpoints.
2.  **Service/Business Logic Layer:** Contains the core business logic, orchestrates operations, and applies business rules (e.g., password policies, note ownership validation).
3.  **Data Access Layer (Repository/ORM):** Abstracts database interactions, performing CRUD operations, handling data mapping, and managing transactions.

## Component Design

### Frontend (Angular - Leveraging Clarity Boilerplate)
*   **Auth Module:** Encapsulates components for user registration, login, and potentially password reset/change. Includes `AuthService` for API interaction and `AuthGuard` for route protection.
*   **Notes Module:** Manages all note-related functionalities. Contains components for:
    *   `NotesListComponent`: Displays a paginated/filtered list of notes. Incorporates search and filter UI.
    *   `NoteDetailComponent`: Displays a single note's content.
    *   `NoteEditorComponent`: Used for creating and editing notes. Integrates a rich text editor and tag input.
*   **Core Module:** (From boilerplate) Provides singleton services like `AuthenticationService` (managing JWT tokens, user state), `ErrorInterceptor` (for global API error handling), and `LoggerService`.
*   **Shared Module:** (From boilerplate) Contains reusable UI components (e.g., custom card, loader, pagination controls), directives, and pipes that are used across multiple feature modules. Will include components related to tag display (e.g., Clarity labels).
*   **Layout Components:** (From boilerplate) `HeaderComponent` (with user profile/logout), `SidebarComponent` (for navigation to notes list, future dashboards).

### Backend (RESTful API)
*   **Authentication Service/Controller:** Endpoints for `/api/auth/register`, `/api/auth/login`, `/api/auth/logout`. Handles user creation, password hashing, JWT generation, and token validation.
*   **User Service/Controller:** Manages user-specific data (e.g., `/api/users/{id}`). Primarily for internal use or administrative purposes, potentially for user profile updates.
*   **Notes Service/Controller:** Provides CRUD operations for notes. Endpoints like `/api/notes`, `/api/notes/{id}`. Includes logic for search, filter, and tagging notes based on user ownership.
*   **Tag Service/Controller:** (If implemented as a separate entity) Manages user-defined tags. Endpoints like `/api/tags`.
*   **Data Access Layer:** Interfaces with the chosen database via an ORM (Object-Relational Mapper). Maps database entities to application objects (e.g., `User` entity, `Note` entity, `Tag` entity).

## Data Architecture
**Database Type:** Relational Database (e.g., PostgreSQL).

### Entities and Relationships:
1.  **User:**
    *   `id` (Primary Key, UUID)
    *   `username` (Unique, String)
    *   `password_hash` (String, for securely stored password)
    *   `email` (Unique, String, Optional if username is primary identifier for login)
    *   `created_at` (Timestamp)
    *   `updated_at` (Timestamp)
    *   *Relationship:* One User has many Notes.

2.  **Note:**
    *   `id` (Primary Key, UUID)
    *   `user_id` (Foreign Key to User.id, Required)
    *   `title` (String)
    *   `content` (Text type, to accommodate rich text/Markdown)
    *   `created_at` (Timestamp)
    *   `updated_at` (Timestamp)
    *   *Relationship:* One Note belongs to one User. Many-to-many with Tags (via `Note_Tag` join table).

3.  **Tag:** (For Phase 2 advanced tagging)
    *   `id` (Primary Key, UUID)
    *   `user_id` (Foreign Key to User.id, Required - Tags are user-specific)
    *   `name` (String, Unique per user)
    *   *Relationship:* Many-to-many with Notes (via `Note_Tag` join table).

4.  **Note_Tag (Join Table):**
    *   `note_id` (Foreign Key to Note.id)
    *   `tag_id` (Foreign Key to Tag.id)
    *   *Composite Primary Key:* (`note_id`, `tag_id`)

### Data Flow:
*   Frontend sends HTTP requests (JSON payload) to backend API.
*   Backend API processes requests, interacts with the database via DAL/ORM.
*   Database stores and retrieves data.
*   Backend sends HTTP responses (JSON payload) back to the frontend.
*   Frontend processes responses, updates UI, and displays data.

## API Design
RESTful API adhering to standard HTTP methods and resource-based URLs. JSON will be the primary data exchange format. All user-specific endpoints will require authentication.

### Authentication Endpoints (`/api/auth`)
*   `POST /api/auth/register`: Create a new user account.
    *   Request: `{ username, email, password }`
    *   Response: `{ userId, username }` (or JWT token directly)
*   `POST /api/auth/login`: Authenticate user and issue JWT.
    *   Request: `{ username, password }`
    *   Response: `{ accessToken, refreshToken (optional), expiresIn }`
*   `POST /api/auth/logout`: Invalidate current user session/token.
    *   Request: (Header: `Authorization: Bearer <token>`)
    *   Response: `{ message: "Logged out successfully" }`

### Notes Endpoints (`/api/notes`)
*   `GET /api/notes`: Retrieve all notes for the authenticated user. Supports query parameters for search and filter.
    *   Query Params: `?search={keyword}&tags={tag1,tag2}&startDate={date}&endDate={date}&page={num}&limit={num}`
    *   Response: `[{id, title, contentSnippet, tags, createdAt, updatedAt}]`
*   `POST /api/notes`: Create a new note for the authenticated user.
    *   Request: `{ title, content, tags: [tag_names] }`
    *   Response: `{id, title, content, tags, createdAt, updatedAt}`
*   `GET /api/notes/{id}`: Retrieve a specific note by ID for the authenticated user.
    *   Response: `{id, title, content, tags, createdAt, updatedAt}`
*   `PUT /api/notes/{id}`: Update an existing note by ID for the authenticated user.
    *   Request: `{ title, content, tags: [tag_names] }`
    *   Response: `{id, title, content, tags, createdAt, updatedAt}`
*   `DELETE /api/notes/{id}`: Delete a specific note by ID for the authenticated user.
    *   Response: `{ message: "Note deleted successfully" }`

### Tags Endpoints (`/api/tags`) - For user-specific tag management
*   `GET /api/tags`: Retrieve all tags for the authenticated user.
    *   Response: `[{id, name}]`
*   `POST /api/tags`: Create a new tag for the authenticated user.
    *   Request: `{ name }`
    *   Response: `{id, name}`
*   `DELETE /api/tags/{id}`: Delete a specific tag by ID for the authenticated user.
    *   Response: `{ message: "Tag deleted successfully" }`

## Security Architecture
*   **User Authentication:** JWT (JSON Web Tokens) will be used for stateless authentication. Access tokens will be short-lived, and optionally refresh tokens can be used for seamless re-authentication.
*   **Password Hashing:** User passwords will be hashed using a strong, adaptive hashing algorithm (e.g., bcrypt) with a sufficient salt value before storage in the database.
*   **Data in Transit:** All communication between the frontend and backend will be secured using HTTPS (TLS/SSL encryption).
*   **Authorization:** Backend API endpoints will implement authorization checks to ensure that a user can only access, modify, or delete their own notes and tags. This will be enforced by validating the JWT and verifying the `userId` associated with the request against the `userId` linked to the resource.
*   **Input Validation & Sanitization:** Both frontend and backend will perform rigorous input validation. Frontend validation provides immediate feedback, while backend validation is critical for security to prevent common vulnerabilities like SQL Injection, XSS (Cross-Site Scripting), and other data integrity issues. Rich text content will require careful sanitization to prevent XSS.
*   **Rate Limiting:** Authentication endpoints (`/api/auth/login`, `/api/auth/register`) will implement rate limiting to mitigate brute-force and denial-of-service attacks.
*   **CORS (Cross-Origin Resource Sharing):** The backend API will be configured to correctly handle CORS policies, allowing requests only from the trusted frontend application origin.

## Scalability Considerations
*   **Stateless Backend:** The use of JWT for authentication will keep the backend stateless, allowing for easy horizontal scaling of API instances.
*   **Database Optimization:** Use of a robust relational database (PostgreSQL) with proper indexing on `userId`, `createdAt`, `updatedAt`, `title`, and `content` (for search) will ensure efficient query performance even with large datasets.
*   **Caching:** For future scalability, a caching layer (e.g., Redis) could be introduced to cache frequently accessed notes or search results, reducing database load.
*   **Containerization:** The application components (frontend, backend, database) will be containerized using Docker, facilitating consistent deployment and scaling in environments like Kubernetes or Docker Swarm.
*   **Modular Frontend:** Angular's modular structure and lazy-loading for feature modules contribute to a scalable and performant frontend by reducing initial bundle size.



---

## ARCHITECTURE UPDATE - 2025-10-02 06:15:56

# Architecture Document
Generated: 2025-10-02T06:14:03.000000

## System Overview
The "Notes App" is a full-stack web application designed for personal note management. It enables users to securely register, log in, and perform CRUD (Create, Read, Update, Delete) operations on their notes. Phase 2 enhancements include advanced features such as search, filtering, rich text editing, and tagging for improved organization. The frontend is built with Angular, leveraging the Clarity Design System from the base project for a consistent and intuitive user interface. The backend will expose a RESTful API to manage user authentication, notes, and associated metadata, ensuring data persistence and security.

## Architecture Pattern
### Client-Server Architecture
The application will follow a classic client-server architecture, where the Angular frontend acts as the client consuming services provided by a dedicated backend API.

### Layered Backend Architecture
The backend will implement a layered architecture to ensure separation of concerns, maintainability, and scalability:
1.  **Presentation Layer (API/Controllers):** Handles HTTP requests, authentication, request parsing, and response formatting. Exposes RESTful endpoints.
2.  **Service/Business Logic Layer:** Contains the core business logic, orchestrates operations, and applies business rules (e.g., password policies, note ownership validation).
3.  **Data Access Layer (Repository/ORM):** Abstracts database interactions, performing CRUD operations, handling data mapping, and managing transactions.

## Component Design

### Frontend (Angular - Leveraging Clarity Boilerplate)
*   **Auth Module:** Encapsulates components for user registration, login, and potentially password reset/change. Includes `AuthService` for API interaction and `AuthGuard` for route protection.
*   **Notes Module:** Manages all note-related functionalities. Contains components for:
    *   `NotesListComponent`: Displays a paginated/filtered list of notes. Incorporates search and filter UI.
    *   `NoteDetailComponent`: Displays a single note's content.
    *   `NoteEditorComponent`: Used for creating and editing notes. Integrates a rich text editor and tag input.
*   **Core Module:** (From boilerplate) Provides singleton services like `AuthenticationService` (managing JWT tokens, user state), `ErrorInterceptor` (for global API error handling), and `LoggerService`.
*   **Shared Module:** (From boilerplate) Contains reusable UI components (e.g., custom card, loader, pagination controls), directives, and pipes that are used across multiple feature modules. Will include components related to tag display (e.g., Clarity labels).
*   **Layout Components:** (From boilerplate) `HeaderComponent` (with user profile/logout), `SidebarComponent` (for navigation to notes list, future dashboards).

### Backend (RESTful API)
*   **Authentication Service/Controller:** Endpoints for `/api/auth/register`, `/api/auth/login`, `/api/auth/logout`. Handles user creation, password hashing, JWT generation, and token validation.
*   **User Service/Controller:** Manages user-specific data (e.g., `/api/users/{id}`). Primarily for internal use or administrative purposes, potentially for user profile updates.
*   **Notes Service/Controller:** Provides CRUD operations for notes. Endpoints like `/api/notes`, `/api/notes/{id}`. Includes logic for search, filter, and tagging notes based on user ownership.
*   **Tag Service/Controller:** (If implemented as a separate entity) Manages user-defined tags. Endpoints like `/api/tags`.
*   **Data Access Layer:** Interfaces with the chosen database via an ORM (Object-Relational Mapper). Maps database entities to application objects (e.g., `User` entity, `Note` entity, `Tag` entity).

## Data Architecture
**Database Type:** Relational Database (e.g., PostgreSQL).

### Entities and Relationships:
1.  **User:**
    *   `id` (Primary Key, UUID)
    *   `username` (Unique, String)
    *   `password_hash` (String, for securely stored password)
    *   `email` (Unique, String, Optional if username is primary identifier for login)
    *   `created_at` (Timestamp)
    *   `updated_at` (Timestamp)
    *   *Relationship:* One User has many Notes.

2.  **Note:**
    *   `id` (Primary Key, UUID)
    *   `user_id` (Foreign Key to User.id, Required)
    *   `title` (String)
    *   `content` (Text type, to accommodate rich text/Markdown)
    *   `created_at` (Timestamp)
    *   `updated_at` (Timestamp)
    *   *Relationship:* One Note belongs to one User. Many-to-many with Tags (via `Note_Tag` join table).

3.  **Tag:** (For Phase 2 advanced tagging)
    *   `id` (Primary Key, UUID)
    *   `user_id` (Foreign Key to User.id, Required - Tags are user-specific)
    *   `name` (String, Unique per user)
    *   *Relationship:* Many-to-many with Notes (via `Note_Tag` join table).

4.  **Note_Tag (Join Table):**
    *   `note_id` (Foreign Key to Note.id)
    *   `tag_id` (Foreign Key to Tag.id)
    *   *Composite Primary Key:* (`note_id`, `tag_id`)

### Data Flow:
*   Frontend sends HTTP requests (JSON payload) to backend API.
*   Backend API processes requests, interacts with the database via DAL/ORM.
*   Database stores and retrieves data.
*   Backend sends HTTP responses (JSON payload) back to the frontend.
*   Frontend processes responses, updates UI, and displays data.

## API Design
RESTful API adhering to standard HTTP methods and resource-based URLs. JSON will be the primary data exchange format. All user-specific endpoints will require authentication.

### Authentication Endpoints (`/api/auth`)
*   `POST /api/auth/register`: Create a new user account.
    *   Request: `{ username, email, password }`
    *   Response: `{ userId, username }` (or JWT token directly)
*   `POST /api/auth/login`: Authenticate user and issue JWT.
    *   Request: `{ username, password }`
    *   Response: `{ accessToken, refreshToken (optional), expiresIn }`
*   `POST /api/auth/logout`: Invalidate current user session/token.
    *   Request: (Header: `Authorization: Bearer <token>`)
    *   Response: `{ message: "Logged out successfully" }`

### Notes Endpoints (`/api/notes`)
*   `GET /api/notes`: Retrieve all notes for the authenticated user. Supports query parameters for search and filter.
    *   Query Params: `?search={keyword}&tags={tag1,tag2}&startDate={date}&endDate={date}&page={num}&limit={num}`
    *   Response: `[{id, title, contentSnippet, tags, createdAt, updatedAt}]`
*   `POST /api/notes`: Create a new note for the authenticated user.
    *   Request: `{ title, content, tags: [tag_names] }`
    *   Response: `{id, title, content, tags, createdAt, updatedAt}`
*   `GET /api/notes/{id}`: Retrieve a specific note by ID for the authenticated user.
    *   Response: `{id, title, content, tags, createdAt, updatedAt}`
*   `PUT /api/notes/{id}`: Update an existing note by ID for the authenticated user.
    *   Request: `{ title, content, tags: [tag_names] }`
    *   Response: `{id, title, content, tags, createdAt, updatedAt}`
*   `DELETE /api/notes/{id}`: Delete a specific note by ID for the authenticated user.
    *   Response: `{ message: "Note deleted successfully" }`

### Tags Endpoints (`/api/tags`) - For user-specific tag management
*   `GET /api/tags`: Retrieve all tags for the authenticated user.
    *   Response: `[{id, name}]`
*   `POST /api/tags`: Create a new tag for the authenticated user.
    *   Request: `{ name }`
    *   Response: `{id, name}`
*   `DELETE /api/tags/{id}`: Delete a specific tag by ID for the authenticated user.
    *   Response: `{ message: "Tag deleted successfully" }`

## Security Architecture
*   **User Authentication:** JWT (JSON Web Tokens) will be used for stateless authentication. Access tokens will be short-lived, and optionally refresh tokens can be used for seamless re-authentication.
*   **Password Hashing:** User passwords will be hashed using a strong, adaptive hashing algorithm (e.g., bcrypt) with a sufficient salt value before storage in the database.
*   **Data in Transit:** All communication between the frontend and backend will be secured using HTTPS (TLS/SSL encryption).
*   **Authorization:** Backend API endpoints will implement authorization checks to ensure that a user can only access, modify, or delete their own notes and tags. This will be enforced by validating the JWT and verifying the `userId` associated with the request against the `userId` linked to the resource.
*   **Input Validation & Sanitization:** Both frontend and backend will perform rigorous input validation. Frontend validation provides immediate feedback, while backend validation is critical for security to prevent common vulnerabilities like SQL Injection, XSS (Cross-Site Scripting), and other data integrity issues. Rich text content will require careful sanitization to prevent XSS.
*   **Rate Limiting:** Authentication endpoints (`/api/auth/login`, `/api/auth/register`) will implement rate limiting to mitigate brute-force and denial-of-service attacks.
*   **CORS (Cross-Origin Resource Sharing):** The backend API will be configured to correctly handle CORS policies, allowing requests only from the trusted frontend application origin.

## Scalability Considerations
*   **Stateless Backend:** The use of JWT for authentication will keep the backend stateless, allowing for easy horizontal scaling of API instances.
*   **Database Optimization:** Use of a robust relational database (PostgreSQL) with proper indexing on `userId`, `createdAt`, `updatedAt`, `title`, and `content` (for search) will ensure efficient query performance even with large datasets.
*   **Caching:** For future scalability, a caching layer (e.g., Redis) could be introduced to cache frequently accessed notes or search results, reducing database load.
*   **Containerization:** The application components (frontend, backend, database) will be containerized using Docker, facilitating consistent deployment and scaling in environments like Kubernetes or Docker Swarm.
*   **Modular Frontend:** Angular's modular structure and lazy-loading for feature modules contribute to a scalable and performant frontend by reducing initial bundle size.
