To build this complex quiz application with extensible features, it's crucial to follow a structured and scalable approach. Here's a step-by-step roadmap tailored to your requirements and a software engineering background:

1. Requirement Analysis and Feature Breakdown

• Understand Features: Break the requirements into smaller, manageable components like authentication, quiz management, quiz-taking process, results display, leaderboard, etc.
• Categorize Features:
  • Frontend: UI components for login, quiz list, quiz-taking, results, leaderboard, admin dashboard.
  • Backend: APIs for user authentication, quiz data, leaderboard generation.
  • Authentication: Implement JWT-based token management.
  • Role Management: Separate admin and user access.

2. Plan the Architecture

• Frontend: Use a framework like React.js.
  • Route management (React Router) for private/public/admin routes.
  • Component-based structure for reusability.
• Backend: Use Node.js with Express or NestJS.
  • API structure for login, registration, quiz handling, and leaderboard.
  • Authentication middleware for JWT.
• Database: Use MongoDB or PostgreSQL for flexibility.
  • Separate collections/tables for Users, Quizzes, Attempts, and Leaderboards.

3. Set Up Development Environment

• Version Control: Set up a GitHub/GitLab repository for version control.
• Project Initialization:
  • Frontend: npx create-react-app quiz-app or Vite for performance.
  • Backend: npm init for the Node.js API.
• Dependencies:
  • Frontend: React Router, Axios, JWT decode, a UI library (e.g., Material-UI, Tailwind CSS).
  • Backend: Express, JWT, bcrypt, dotenv, MongoDB/Prisma.
  • Testing: Jest (for unit testing) and Cypress (for end-to-end testing).

4. Build Incrementally (Feature-by-Feature Development)

Frontend Development:

1. Authentication:
   • Create login and registration forms.
   • Handle JWT tokens for user sessions.
   • Set up role-based redirects (user/admin).
2. Home Page:
   • Fetch and display quizzes from Quiz List API.
   • Conditional rendering of the welcome section (logged-in users only).
3. Quiz Page:
   • Design question display with "Next" button functionality.
   • Randomize options using Array.sort() on each render.
   • Sidebar to track answered and remaining questions.
4. Results Page:
   • Calculate marks and display circular progress bar (e.g., react-circular-progressbar).
   • Highlight correct/incorrect answers.
5. Leaderboard:
   • Generate and display sorted data (client-side leaderboard logic).

Backend Development:

1. APIs for User Management:
   • Endpoints for login, registration, token refresh.
2. APIs for Quiz Management:
   • CRUD operations for quizzes (add, update, delete).
   • Quiz participation status tracking.
3. APIs for Results and Leaderboard:
   • Submit quiz attempts.
   • Fetch sorted leaderboard data for a quiz set.

5. Implement Role-Based Access Control

• Use middleware in the backend to validate JWT tokens and user roles.
• Protect private routes in React with route guards.

6. Testing and Iteration

• Frontend: Test each component and route.
• Backend: Test APIs using Postman and automated tests.
• Integration Testing: Ensure smooth interaction between frontend and backend.
• End-to-End Testing: Use tools like Cypress for user flows.

7. Deployment and Future Scalability

• Deployment:
  • Frontend: Deploy on Vercel or Netlify.
  • Backend: Deploy on Heroku or AWS.
• Future Features:
  • Modularize the codebase for easier updates.
  • Maintain a roadmap for upcoming features.

8. Documentation and Maintenance

• Create clear documentation for:
  • APIs and endpoints.
  • User and admin functionalities.
• Use tools like Swagger for API documentation.

By following this roadmap, you can build your application systematically, ensuring it remains extensible and maintainable for future updates. Start small, validate features as you go, and iteratively improve.